Integrated Disease Management Team | 2024 Progress Report

View all tables and figures in pages 65 – 98 of the pdf version of this report.

Integrated Disease Management Team and Personnel Working on Project

Lina Quesada-Ocampo (NC State)
- Yara Rosado (technician)
- Mary Lorscheider (extension communicator)
- Mariana Prieto (PhD student)
- Ziaur Bhuyian (Postdoc)
Mary Hausbeck (MSU)
- Cheryl Engfehr (Extension support specialist)
- Carmen M. Medina-Mora (technician)
- David Perla (Research Technician)
- John Spafford (Graduate student)
Chris Smart (Cornell)
- Colin Day (lab manager)
- Taylere Herrmann (technician)
- Libby Indermaur (PhD student)
- Emma Nelson (PhD student)
Anthony Keinath (Clemson)
- Sierra Zardus
- Anna Mothersbaugh
Shaker Kousik (USDA-ARS)
- Jennifer Ikerd
Jonathan Schultheis (NC State)
- Stuart Michel (Technician/MS Student)
- Brandon Parker (Research Associate)
- Baker Stickley (Technical Support – Hourly)
- Andrew Pfefferkorn (Technical Support – Hourly)
- Kaleb Holder (Technical Support – Hourly)
Daniel Tregeagle (NC State)
- Alice Kilduff (PhD Student)

4.1. Disease management information and recommendations (Year 1-4).

CucCAP website: From Sept. 1, 2020 until Feb. 29, 2024, the CucCAP website was visited by 52127 users with 65868 sessions and 143713 pageviews. A total of 475 news items were posted on the website including 280 posts of news from the CucCAP researchers and 320 crop and disease reports from regional Vegetable specialists. These posts were shared in 35 monthly newsletters sent to 167 subscribers since October 2020. Posts on the CucCAP website are social media including Facebook with 199 followers, Twitter with 318 followers, and LinkedIn with 41 followers. Cucurbit disease factsheets and links to integrated pest management resources are maintained and updated annually on the website. The CucCAP website events calendar shared notices of 75 regional commodity meetings, 53 education sessions, and 28 Scientific meetings.
Quesada: Since the start of the project, Quesada has provided diagnostics and disease management recommendations for 28 cucumber, 52 watermelon, 12 melon, 20 squash, and 15 pumpkin samples submitted to the NC State Plant Disease and Insect Clinic. Quesada has also been involved in providing disease management recommendations through oral presentations, social media (Twitter: 7,483 (lab) + 4,101 (Quesada) followers, LinkedIn: 3,341 followers), and generating disease management resources such as the NC Agricultural and Chemicals Manual and the Southeastern US Vegetable Crop Handbook.
Schultheis provides cultivar/advance line (cultigen) study results that are posted regularly on the North Carolina State University cucurbit portal and shared on the CucCAP website.
Keinath posts disease management articles during the growing season in the SC Grower blog and in the American Vegetable Grower online magazine.
Smart provided recommendations to growers and extension educators across NY. Between August 2023 – March 2024, she responded to 123 text messages and 47 email messages about cucurbit diseases. Additionally, she made 7 farm visits including farms on Long Island, Hudson Valley, Capital District, and Western NY.
Hausbeck maintains a dedicated downy mildew page and fact sheets for Phytophthora on cucurbits.

4.2. Perform Multi-location, multi-isolate trials and pathogen population analyses. 4.2.1 Evaluation of cucurbit cultivars and breeding lines for disease resistance (Year 1-2).

Watermelon powdery mildew

(Lead: Kousik, Secondary Site: Quesada):

Kousik (2021, 2022):

Powdery mildew (PM) of watermelon (Citrullus lanatus) caused by Podosphaera xanthii is a major factor limiting production in greenhouses and open fields. In recent years, occurrence of PM has been increasing on watermelon across the United States. The disease continues to be a constant problem throughout the southeast. Our survey of watermelon researchers also indicated that powdery mildew was considered an important priority for research across the U.S.A. Several seed companies have developed commercial seeded and seedless watermelon varieties with powdery mildew resistance. The objective of this part of the project was to evaluate commercial watermelon varieties from seed companies for their reaction to locally prevailing powdery mildew pathogen in South Carolina. Experiments were conducted in 2021 and 2022 at the U.S. Vegetable Laboratory farm in Charleston, SC. The soil at the farm was Yonges loamy fine sand. The experimental design was a randomized complete block with four replications for each variety. Watermelon varieties were seeded in 50-cell jiffy trays and four-week-old seedlings were transplanted onto 91-cm wide raised. Beds were spaced 4.6 meters apart and covered with white plastic mulch. Plants were irrigated weekly using subsurface drip irrigation using a drip tape placed 2.54-cm below the top of the plastic mulched beds. Each variety plot was a single row of 5 plants spaced 46-cm apart with 2.7 meters spacing between plots. Vines of the watermelon plants were regularly turned every week so as to keep the plants from growing into the neighboring plots. Plants of germplasm line USVL677-PMS and cultivar Mickey Lee were used as susceptible controls. A USDA, U.S. Vegetable Laboratory developed germplasm line, USVL608-PMR resistant to powdery mildew was used as the resistant control. After bedding but before planting, the row middles were sprayed with Roundup Pro (1 pt/A), Dual Magnum (1 pt/A) and Sandea (1 oz/A) for weed management. Weeds between beds were controlled during the season with spot application of Roundup and by hand weeding. Powdery mildew occurs naturally at this location every year and hence plots were not inoculated. Plant foliage for each variety plot was rated for powdery mildew in 2021 on 22, 29 June, 6, 13 and 20 July using a 0-10 rating scale similar to the Horsfall and Barrett rating scale of increasing disease severity (0=no visible symptoms of disease observed, 1=trace <1-3% on foliage, 2=3-6%, 3=6-12%, 5=25-50%, 7=75-87%, and 10= 97-100% area of leaf covered with PM). In 2022 seven weekly ratings were taken from May severity. 26 to July 8 as done during 2021. During each rating period ratings were recorded on lower leaves in the canopy. The underside of five lower leaves for each plot was observed to provide rating for each plot. The ratings were converted to the mid percentage points for analysis. Area under disease progress curves (AUDPC) was calculated for each plot and means were separated using Fisher’s protected LSD (α=0.05).

A significant difference (P≤0.0001) in the response of watermelon varieties to powdery mildew over time was observed in both years (Table 1). The appearance of powdery mildew on these varieties was confirmed by the presence of conidia of the pathogen on the leaf surface microscopically. Significant
disease development was observed on the susceptible cultivars USVL677-PMS and Mickey Lee, especially during the third and fourth ratings taken on 6 and 13 July in 2021. Based on AUDPC, all commercial varieties and the germplasm line USVL608-PMR and SP-6 were significantly more resistant compared to the susceptible controls in both years. In 2022 powdery mildew development was a little more severe and was observed on all the commercial varieties by end of the season (Table 1).

Table 1. Reaction of commercial watermelon varieties to natural powdery mildew infection at the U.S. vegetable Laboratory Farm in Charleston SC in 2021 and 2022.

Quesada (2021):

The experiment was conducted at the Cherry Research Farm in Goldsboro, NC. Plots were single raised beds on 10-ft centers covered with white plastic mulch; 14-ft long with 10-ft fallow borders on each end and a non-treated guard row on one side. The previous year the field was planted
with cucumber. Watermelon was transplanted on 21 May (2-ft in-row spacing, 7 plants/plot). Irrigation and fertilization (4-0-8, N-P-K) were applied via drip tape. Watermelon varieties were randomized into four complete blocks. Disease severity was assessed on 16, 23 and 30 Jul and 5 Aug as percentage of total area colonized by P. xanthii. Data were analyzed in the software ARM (Gylling Data Management, Brookings, SD) using analysis of variance (AOV) and Fisher’s Protected LSD test to separate means.

Powdery mildew was first detected on 7 Jul at approximately 1% disease severity in the field. Disease progressed throughout the course of the experiment. ORS6406A and Embassy had the lowest levels of P.xanthii. The varieties Suprema, USVL 608, 7197 HQ, Excite and Summerlicious all had low levels of disease as well. In the table, varieties are sorted by the final disease severity rating on 5 Aug.

Quesada (2022):

This experiment was conducted at the Cherry Farm Research Station in Goldsboro, NC. Research plots were single raised beds on 5-ft centers covered with white plastic mulch; 14-ft long with 10- ft fallow borders on each end. Watermelon was seeded on 5 Jun in the greenhouse, thinned to one plant per cell after emergence (2 seed/cell), and transplanted to the field on 15 Jun (2-ft in-row spacing, 7 plants/plot). Irrigation and fertilization (4-0-8, N-P-K) were applied via drip tape. Thirteen cultivars were evaluated in a randomized complete block design with four repetitions. Disease severity per plot was assessed on 7, 14, 19, 25 July and 2, 9, 19 and 25 Aug. Data were analyzed in the software ARM (Gylling Data Management, Brookings, SD) using analysis of variance (AOV) and Fisher’s protected least significant differences (LSD) test to separate means.

Powdery mildew was first detected on 19 Jun at approximately 1% disease severity in the field. At the disease severity data obtained on 25 Aug the varieties Embasy and 50036 were statistically different from the varieties Mickey Lee and USVL677-PMS (susceptible checks). All varieties were statistically better than the susceptible check. The disease summary for the season (AUDPC) showed that all the varieties were statistically different from the susceptible checks (Mickey Lee and USVL677-PMS).

Watermelon Fusarium wilt

(Lead: Schultheis, Secondary Site: Keinath):

Schultheis (2021, 2022):

North Carolina studies were conducted in a Fusarium-infested field at the Central Crops Research Station, in Clayton NC in 2021 and 2022. Fusarium races 1, 2 and a virulent race 2 or race 3 were reported based on differential testing conducted by Syngenta in 2021. Ten commercial triploid watermelon cultigens (cultivars or advanced lines) were evaluated in 2021 and 12 cultigens were evaluated in 2022; with eight common cultigens being tested each year. There was a 92% correlation between plants with Fusarium wilt symptoms and yield (i.e., lower Fusarium wilt incidence resulted in higher watermelon yields). Ten weeks after transplant, nine of the 10 entries had 75 to 100% Fusarium wilt incidence. Disease incidence was lowest in the Fascination cultivar and disease occurrence lagged behind the other cultivars over time. No Fusarium wilt incidence occurred when the Fascination cultivar was grafted to Carolina Strongback rootstock. Grafted Fascination plants yielded 1.9 marketable size fruit per plant which was superior when compared with all cultivars. The second highest yielding cultivar was Fascination which yielded 0.6 fruits per plant while all other cultivars yielded similarly producing 0.1 to 0.4 marketable fruit per plant. In 2022, two advanced Syngenta lines and 2 advanced HM Clause lines were included in the study to see if better Fusarium wilt tolerance could be achieved than in 2021. Fascination grafted to Carolina Strongback had the lowest Fusarium incidence (8%) 9 weeks after transplant (WAT). The cultivars in 2022 that were common to those evaluated in 2021 had a similar high Fusarium incidence (80 to 100%) 9 WAT. The two Syngenta lines were susceptible to Fusarium wilt (>90%) 9 WAT. HMC633810 (Eleanor) had the lowest Fusarium incidence (50%) on non-grafted plants 9 WAT. Although fruit sizes in 2022 were smaller than in 2021, total fruit weight per plot was highest with grafted Fascination, followed by Eleanor and was lowest with Shoreline which had 100% Fusarium incidence 9.WAT. The R square value between yield and disease incidence was 0.84.

Keinath (2021, 2022):

The South Carolina trials were done in a Fusarium-infested field at the Clemson Coastal REC, a field that has had Fusarium races 1 and 2 in it since 2005. Ten cultivars were tested in 2021 and 12 cultivars were tested in 2022; eight cultivars were tested both years. The correlation between marketable weight per acre and the percentage of wilted plants at the end of the season (10 weeks in 2021 and 11 weeks in 2022) was highly significant (r = -0.97, P = 0.001). Based on this correlation, Fusarium wilt was the main reason yields differed among the eight cultivars. Fascination grafted onto Carolina Strongback citron rootstock yielded 40,000 pounds per acre and had no plants wilted (0 of 96 plants examined in the 2 years). On the other hand, Shoreline had the lowest yields in both years and the highest percentage of wilted plants. Disease ratings were similar for each cultivar in the two years, although disease was more severe in 2022 than in 2021. For example, the final wilt percentage on Shoreline was 68% in 2021 and 94% in 2022. Fusarium wilt symptoms continued to appear in 2022 after harvest started, likely due to the extremely dry conditions in June and high temperatures. Yields did not differ significantly between years. Postharvest quality was measured, but, in general, there were few differences among the cultivars. Hollow heart was relatively low, and most fruit with hollow heart had small cracks. There were more seeds per fruit in 2021 than in 2022. In 2022 grafted Fascination had more seeds per fruit, an average of 0.9 seed, than all other cultivars. In 2021, cultivars with more diseased plants had lower Brix, while Brix was relatively high for all cultivars in 2022, likely due to the dry weather. Flesh firmness differed among cultivars in both years; however, firmness varied each year. In general, Shoreline had the firmest fruit both years, firmer than all other cultivars.

Cucumber downy mildew

(Lead: Hausbeck, Secondary Site: Quesada):

Hausbeck (2021):

To evaluate cucumber cultivars and breeding lines for downy mildew (DM) resistance under Michigan’s field conditions, a total of 4 pickling cucumber cultivars and 5 breeding lines were included in a field trial located at Michigan State University Plant Pathology Farm (MSU-PPF) in Lansing, MI. Prior to planting, the field was prepared following commercial production standards; the Capac loam soil was plowed and disced on 20-May and 1-Jun., respectively, and amended with 100 lb Urea and 45 lb Potash on 1-June. On 26-Jul., all seeds (80 seeds per cultivar or line) were directly seeded every 12 in onto raised beds (rows 20ft long, 8ft from center to center). Cultivars and lines were distributed in a complete randomized block design with four replications. To monitor natural DM infection, trap plants of the susceptible cultivar ‘Valspik’ were planted in an adjacent field. On 25-July, high levels of DM infection and typical DM symptoms were observed on trap plants. Starting on 15- August, Quadris (15.5 fl oz) and Torino (3.4 fl oz) were applied, as needed, to control the incidence of Alternaria and powdery mildew, respectively. Disease ratings (% foliar infection) were performed on 24-and 29-Aug., and 5-September. The percentage of foliage with downy mildew symptoms and area under the disease progress curve (AUDPC) were calculated at the end of the season. Data were analyzed with SAS statistical software, version 9.4, using the PROC GLIMMIX procedure for a one-way ANOVA, with mean separation performed using Fisher’s least significant difference (LSD) with a Tukey’s adjustment.

On 24-August, disease severity in the susceptible check (‘Straight-Eight’) was 26.3% and increased significantly on 29-August (86.3%). On 29-August, ‘Straight-Eight’ was not different from ‘Liszt’, ‘Gy14DH’, and ‘WI7822’ but had more disease than all other cultivars. On 5 September, all cultivars had significantly less disease than ‘Straight-Eight’ except ‘Liszt’ and ‘WI7822’; ‘WI7088D’ had significantly less disease (4.8%) than all other cultivars except ‘Chaperon’ and ‘Peacemaker’. According to the area under the disease progress curve (AUDPC), ‘WI7088D’ was not different from ‘Chaperon’, ‘Citadel’, or ‘Peacemaker’. Overall, this study shows that multiple cultivars evaluated (‘WI7088D’, ‘Chaperon’, ‘Peacemaker’, and ‘Citadel’) show moderate levels of resistance to the downy mildew pathogen, Pseudoperonospora cubensis, under natural infection conditions under high pathogen pressure in Michigan.

Quesada (2021):

The experiment was conducted at the Horticultural Crops Research Station in Clinton, NC. Plots were single raised beds on 5-ft centers covered with white plastic mulch; 14-ft long with 5-ft fallow borders on each end and non-treated guard rows on each side. This field was planted with cucumbers in 2020. Cucumber was directly seeded on 11 Aug (2-ft in-row spacing, 2 seed/hill) and thinned to one plant per hill after emergence (7 plants/plot). Irrigation and fertilization (4-0-8, N-P-K) were applied via drip tape. Cucumber varieties were randomized into four complete blocks. Disease severity was assessed on 14, 23 and 29 Sep, 6 and 13 Oct as percent leaf area with necrosis per plot. Fruits were harvested on 22 and 27 Sep, 5 and 12 Oct. Data were analyzed in the software ARM (Gylling Data Management, Brookings, SD) using analysis of variance (AOV) and Fisher’s protected least significant difference (LSD) test to separate the means.

Downy mildew was first detected on 31 Aug at approximately 1% disease severity in the field and progressed throughout the course of the trial. PI-197088 had the lowest level of disease. All varieties were significantly better than the standard (Lizst) besides the Gy14. For the total marketable weight, the variety PI-197088 had the highest weight. For the total unmarketable, the variety Jumbo G/L had the most weight.

Quesada (2022):

The trial was performed at the Horticultural Crops Research Station in Clinton, NC. Experimental plots were single raised beds on 5-ft centers covered with white plastic mulch; 14-ft long with 5-ft fallow borders on each end and non-treated guard rows on each side. Cucumber varieties were directly seeded on 21 Jun (2-ft in-row spacing, 2 seed/hill) and thinned to one plant per hill after emergence (7 plants/plot). Regular cultural practices like irrigation and fertilization (4-0-8, N-P-K) were applied via drip tape. Twelve cultivars were tested in a randomized complete block design with four repetitions. Disease severity per plot was assessed on 20 and 29 Jul, 3, 10, 17 and 24 Aug. Data were analyzed in the software ARM (Gylling Data Management, Brookings, SD) using analysis of variance (AOV) and Fisher’s protected least significant differences (LSD) test to separate means.

Downy mildew was first detected on 18 Jul at approximately 5% disease severity in the field. The disease severity data obtained on 10 Aug, 7 weeks after planting the variety Peacemaker, was statistically different from the variety Liszt (susceptible control) but not for other varieties. The disease summary for the season (AUDPC) showed that all cucumber cultivars were statistically different from Lizst except the cultivar WI7821, being Peacemaker with the lowest disease value. Yields were assessed every week (4 data points) as marketable and non-marketable (summarized as total marketable and total non-marketable). For the marketable yields the variety Peacemaker and Chaperon were statistically better from the variety Liszt, but not for other treatments. For the non-marketable yields Gy14Q2 was the variety with more weight per treatment compared with Jumbo G/L that got the lowest weight per treatment.

Squash powdery mildew

(Lead: Smart, Secondary Site: Hausbeck)

Smart (2022):

Trial 1: To evaluate C. pepo accessions from the USDA germplasm collection, for PM resistance, Smart evaluated 198 lines (the same lines as the 201 that Hausbeck evaluated, but three accessions died in our hands). We evaluated the accessions in the greenhouse, with three replicates per accession and 5 plant plots in a randomized complete block design. Plants were rated once, two weeks after inoculation with Podosphaera xanthii conidia from leaves that were naturally infected in the field. Ratings were taken as % diseased leaf area on the surface of top 4th leaf, bottom 4th leaf, stem above 4th leaf, and stem below 4th leaf. Overall mean disease severity was highest in top 4th leaf (88.5%), followed by stem below 4th leaf (22.3%), bottom 4th leaf (9%), and least in stem above 4th leaf (6.5%). The accession Success PM was consistently resistant across reps, and accession 189 was also resistant.

Trial 2: The Smart lab also conducted a field trial with 6 C. moschata breeding lines for fruit processing quality, from Michael Mazourek’s program. Plots were rated once for powdery mildew severity. This trial included 1 resistant parent, 1 susceptible parent, and 4 progeny. Representative fruit from each treatment were canned in fall 2022 to assess canning yield, dry matter, water separation, and color. Cultivars Butterfly and Bugle were more resistant than the others tested.

Hausbeck (2022):

To evaluate squash breeding lines for powdery mildew (PM) resistance under Michigan’s field conditions, a total of 201 entries from GWAS panel received from Cornell University (Mazourek) and University of Florida (Meru) were included in a strip field trial located at Michigan State University Southwest Michigan Research and Extension Center (SWMREC) in Benton Harbor, MI. Prior to planting, the field was prepared following commercial production standards; the sandy soil was plowed and disced on 20-May and 1-Jun., respectively, and amended with nitrogen (100lb/A), potassium (180lb/A), sulfur (25lb/A), and boron (2lb/A) on 31-May. On 23-August, all seeds (30 seeds per entry) were directly seeded every 6 inches onto raised beds (rows 15ft, 8 ft center to center) with no buffer rows. Each plot was divided into 3 “pseudoplots”, where each pseudoplot consisted of a maximum of 10 plants. A field of squash (cv. ‘Yellow squash’) heavily PM infected and adjacent to the strip trial served as natural inoculum for this trial. To monitor natural PM infection, the development of PM colonies on susceptible lines were observed weekly, and disease rating was performed when at least 40 % of the foliage for the entire plot (i.e. max. 30 plants) of selected susceptible lines had PM colonies. On 10- October, 20 days after the first PM colonies were observed, the fourth leaf of one plant per pseudoplot was rated for % foliar infection at adaxial and abaxial surfaces and % coverage at the internodes below and above the fourth leaf. Overall, 63% (126 out of 201 entries) of the lines evaluated had an overall disease rating of less than or equal to 20% PM infection and 25% (50 out of 201 entries) of the lines evaluated had an overall disease rating of less than or equal to 40% PM infection. No single line evaluated had 100% PM infection, however 6% (13 out of 201 entries) of the lines evaluated had an overall disease rating of less than or equal to 80% PM infection. Lines with more than 40% PM should be considered susceptible while lines with 0% PM infection should be considered resistant to PM infection under the conditions of this trial. A total of 6 lines (3% of the total entries) had zero PM infection but the seed germination rate for these lines was reduced. A total of 6 lines (3% of the total entries) were not evaluated due to zero germination for these lines.

Hausbeck (2023)

To Evaluate efficacy of biopesticides for control of powdery mildew on intermediately resistant acorn squash. The trial was established at the Michigan State University Plant Pathology Farm in Lansing, MI, in a field of Capac loam soil previously planted to squash. The field was plowed on 9 May and disced 15 May. Preplant fertilizer (130 lb/A urea and 130 lb/A potash) was applied and incorporated on 16 May. On 17 May, raised beds were formed in the field with black plastic mulch 12-ft apart with drip tape for irrigation and in-season fertilization. Biweekly mechanical cultivation and hand weeding was used for weed control. Planting occurred 31 May via transplanting Using three weeks olds seedlings. The cultivar used for this experiment was intermediately resistant ‘Tiptop’. The treatments were arranged in a randomized complete block design with four replications. Each replication was 20 ft long with a 5-ft buffer between each plot in a row. Each week during the growing season the trial was fertilized with urea ammonium nitrate (28% N) at 1 gal/A through the drip tape. Admire Pro SC (10.5 fl oz/A) was applied through the drip tape on 5 and 24 Jul and Warrior CS (1.92 fl oz/A) was sprayed on 28 Jul for insect control. Spray treatments were applied on 19 and 27 Jul; 2, 9, 16, 24 and 31 Aug; and 7 Sep using a CO2 backpack sprayer and a broadcast boom equipped with four XR8003 flat-fan nozzles spaced 18 in. apart, calibrated at 35 psi, and delivering 50 gal/A. Foliage was evaluated for disease severity (both upper and lower surface of the leaf) on 3, 14, 24 and 30 Aug; 7 and 14 Sep and for necrosis on 24 and 30 Aug; 7 and 14 Sep. Evaluations were conducted using a 0 to 100 % scale, with 0% = 0% foliar disease/necrosis and 100% = 100% foliar disease/necrosis. Area under the disease progress curve was calculated for the upper and lower leave surface and for necrosis using disease severity data. Data were analyzed using an analysis of variance (ANOVA) with means separation performed using Fisher’s protected least significant difference (LSD).

According to disease severity on the final rating date, there were no differences among treatments for either the upper or lower leaf surfaces. On the upper leaf surface, all treatments limited the area under the disease progress curve (AUDPC) compared to the untreated control except for Zonix L 500 ppm plus Kinetic L 6 oz/100 gal. No differences among treatments were observed for AUDPC on the lower leaf surface. According to the foliar disease severity on the final rating date, only treatments that included Sil Matrix 3 qt./ 100 gal limited necrosis compared to the untreated control. According to AUDPC, only Zonix L 500 ppm plus Sil-Matrix SC 3 qt./ 100 gal had less disease than the untreated control.

Squash Phytophthora blight

(Lead: Hausbeck, Secondary Site: Smart):

Hausbeck (2022):

To evaluate squash cultivars and breeding lines for Phytophthora crown and rot resistance under Michigan’s field conditions, a total of 30 squash breeding lines received from Cornell University (Mazourek: 16 entries) and University of Florida (Meru: 14 entries) were included in two independent trials (Trial 1 and Trial 2). Field plots were established at SWMREC, Benton Harbor, MI. Prior to planting, fields were prepared following commercial production standards: the sandy soil was plowed and disced, and amended with nitrogen (100lb/A), potassium (180lb/A), sulfur (25lb/A), and boron (2lb/A) on 31-May. For Trial 1 (Mazourek), on 7-Jul., thirty 3-week-old seedlings per line were transplanted onto raised beds covered with black polyethylene plastic at 18in apart from each. For Trial 2 (Meru), on 16-Aug., twenty 3-week-old seedlings per line were transplanted onto raised beds at 18in apart from each. Lines for each trial were distributed in a complete randomized block design with four (Mazurek) or three (Meru) replications. On 22-Jul. and 30-Aug. for Trial 1 and Trial 2, respectively, each plant was inoculated with 1 g of P. capsici (M. Hausbeck P. capsici collection, strains SP98 and 12889) at a 1:1 ratio) infested millet placed at the crown of each plant. On 12-Aug. and 12-Sept., the first symptoms of Phytophthora crown rot were observed in the susceptible control lines; 22-T1B-13 (‘Golden Delicious’) for Trial 1 and ‘Early Prolific’ for Trial 2. Plant death assessments were performed on; 12-, 19-, 26-Aug. and 1-, 6-, 13-Sept. for Trial 1, and 7-, 20-, and 27-Sept. for Trial 2. For both trials, the area under the disease progress curve (AUDPC) was calculated at the end of the season and data were analyzed with SAS statistical software, version 9.4, using the PROC GLIMMIX procedure for a one-way ANOVA, with mean separation performed using Fisher’s least significant difference (LSD) with a Tukey’s adjustment.

For Trial 1, on 12-August plant death in the susceptible line 22-T1B-13 (‘Golden Delicious’) was 1.9% and increased significantly on 13-September (75.3%). On 13-September, 5 lines (22-T1B-08, 22-T1B-06, 22-T1B-09, 22-T1B-10, and 22-T1B-11) were as susceptible as ‘Golden Delicious’. Five lines (22-T1B 02, 22-T1B-04, 22-T1B-05, 22-T1B-07, and 22-T1B-12) were as resistant as the intermediate F1 lines 22- T1B-014 and 22-T1B-15 (‘Autumn Cup’ and ‘Thunder’, respectively) and the resistant line 22-T1B-16 (‘Dickinson’). Resistance on 2 out of the 12 experimental lines tested (22-T1B-01 and 22-T1B-03) is still under segregation since plant death was not different from susceptible and resistant control lines. According to the area under the disease progress curve (AUDPC), 4 out of the experimental lines evaluated (22-T1B-02 22-T1B-04, 22-T1B-05, and 22-T1B-07) show promising levels of resistance to P. capsici.

For Trial 2, on 12-September plant death in the susceptible cultivar ‘Early Prolific’ was 44.4% and increased rapidly and significantly on 20-September (94.4%). On 27-September, one line (358-174) showed moderate resistance as moderate resistant controls (PI181761-36p-Lot 1 and PI181761-36p-Lot 3) and resistant control (SSS333-7). Three lines (SS2147, SS2071, and SS2078) were as resistant as the resistant controls (SS333-8 and SS69-72). According to the area under the disease progress curve (AUDPC), 3 out of the 10 experimental lines evaluated (SS2147, SS2071, and SS2078) show promising levels of resistance to P. capsici and 3 lines (358-195, SS792-2, and 358-164) are still under segregation.

Table: Trial 1 (Seed lot supplied by M. Mazourek-Cornell, NY)

Table: Trial 2 (Seed lot supplied by G. Meru-Univ. of Florida, FL)

To evaluate breeding lines for Phytophthora fruit rot Age-Related Resistance (ARR), fruits from a total of 12 squash breeding lines and 4 squash cultivars were collected from the field and infected with P. capsici (strain SP98) under laboratory conditions. A pollination plot was established at MSU-PPF, East Lansing, MI and prepared following commercial production standards; the Capac loam soil was plowed and disced on 20-May and 1-Jun., respectively, and amended with 100 lb Urea and 45 lb Potash on 1-June. On 7-Jul., transplants (30 seeds per cultivar or line) were directly seeded every 18 in onto raised beds (rows 100ft X 16ft center to center) covered with black polyethylene plastic. Until fruits were harvested, 28% fertilizer (1gal/A) was applied weekly and non-target diseases and insects were controlled. Starting on 7-Sept., a mixture of Torino (3.4 fl oz) and Bravo (32 fl oz) was applied, as needed, to control the incidence of powdery mildew, and Admire Pro (10.5 fl oz) was delivered through drip tape to control insects. To facilitate fruit set and reduce natural flower abortion, flowers at anthesis were hand-pollinated using an artist’s paint brush and marked at the petiole using colored-flagging tape. Because flower development among the lines was asynchronized, the presence of flowers at anthesis in each line was monitored daily for 30 days and hand-pollination was performed every other day during this time. A total of 790 flowers were hand-pollinated to harvest a maximum of 12 fruits corresponding to 21 days post-pollination (dpp) and 12 fruits corresponding to 28dpp per line. A 4 mm mycelial plug of a 7-day-old culture of P. capsici (strain SP98) was placed onto the surface/epidermis of each disinfected fruit on the same day each fruit was harvested. Fruit rot was evaluated 5 days post-inoculation (dpi) and disease assessment included: 1) lesion size, 2) incidence of hyphae beyond inoculation point, and 3) disease severity based on a 0-4 categorical scale (0= healthy, 1=water-soaked lesion, 2= light mycelial growth, 3=moderate mycelial growth, 4= severe mycelial growth).

Overall, fruits corresponding to 3 breeding lines (22-T1A-02, 22-T1A-11, and 22-T1A-12) show a reduction of disease incidence (%) over time. A 30-60% incidence of fruit rot was observed when fruits corresponding to 21dpp were inoculated with P. capsici, however fruit rot was not observed for fruits corresponding to 28dpp from the 3 experimental lines indicated above. These results indicate age-related resistance for these 3 lines as previously observed for resistant control lines 22-T1A-14 (‘Autumn Cup’) and 22-T1A-16 (‘Dickinson’).

Table: Percent Disease Incidence and Probability of Fruit Rot Incidence

To evaluate squash breeding lines for Phytophthora crown and root rot resistance at the seedling stage, a greenhouse trial at Michigan State University Plant Science Greenhouses in East Lansing, MI was established. The trial consisted of a total of 8 interspecific breeding lines (BC2F1) and 3 parental lines provided by Dr. Mazourek (Cornell Univ.). On 26-May, 18 seeds per line were directly seeded onto 3x3in plastic containers containing SureMix soilless medium. On 29-June, when seedlings were at 3-4 leaf stages, all seedlings were inoculated with a zoospore suspension (2×104/ml) of Phytophthora capsici (M. Hausbeck P. capsici collection, strains SP98 and 12889). Lines were distributed in a complete randomized block design with three replications. Disease ratings based on a 0-5 categorical scale (0= healthy, 1=small lesion at crown, 2= water-soaked lesions beyond cotyledons, 3=wilt and plant partially collapsing, 4= severe wilt and pant completely collapsing, and 5=plant death) were conducted once a week after inoculation on 7-, 13-, and 20-July. A preliminary analysis of the results indicated differences in resistance among the lines tested; 2 lines were more susceptible than the susceptible parental line (cv. ‘Golden Delicious’) and 6 lines were more susceptible than the resistant parental lines (cv. ‘Dickinson’ and F1:21-2253×2262). Furthermore, differences in response among the individuals (i.e. each seedling) within each line indicated that resistance is still segregating.

Table: Average disease rating of Breeding Lines

Smart (2022):

Trial 1: Greenhouse trial of 14 squash breeding lines with potential resistance to Phytophthora capsici from Geoffrey Meru performed in a RCBD and inoculated with a NY isolate of Phytophthora capsici. Breeding line SS69-72 had a significantly lower AUDPC relative to all other lines except SSS337-7. Line SSS337-7 had a significantly lower AUDPC than 358-174, 358-195, and Early Prolific. All other AUDPC values between breeding lines were not significantly different from each other.

Trial 2: Field trial with 16 C. maxima accessions for fruit processing quality, from Michael Mazourek’s program. This included 12 entries and 4 controls. Representative fruit from each treatment were canned in fall 2022 to assess canning yield, dry matter, water separation, and color.

Hausbeck 2023

To Evaluate efficacy of conventional and biorational products to control Phytophthora crown rot of cucurbits using a partially resistant hard squash ( Cucurbita maxima) cultivar. This study was conducted at the Michigan State University Southwest Research and Extension Center located near Benton Harbor, MI on sandy soil previously planted to squash. The field was plowed, disced, and preplant fertilizer (potassium 180 lb/A, sulfur 25 lb/A, and boron 2.0 lb/A) was applied on 19 May. On 26 May, 6- in. raised plant beds covered with black polyethylene plastic were laid spaced 16 ft apart. A single drip tape (0.65 gpm/100 ft) was installed under the plastic mulch for plot irrigation. On 2 Jun, 3-week-old ‘Thunder’ winter squash plants were transplanted 18 in. apart. Fertilizer (urea ammonium nitrate 28% N) was applied weekly at a rate of 1 gal/A/day through the drip tape. For each treatment, a replicate consisted of a single 20-ft row with a 5-ft buffer within the row to separate treatments. Treatments were arranged in a randomized complete block design with four replicates. On 23 Jun, plants were inoculated with P. capsici-infested millet (100 g sterilized millet, 72 ml distilled water, 0.08 g asparagine, and 7 7-mm plugs of P. capsici). P. capsici isolates 12889 (A1 mating type, sensitive to mefenoxam, isolated from cucumber) and SP98 (A2 mating type, sensitive to mefenoxam, isolated from pumpkin) were used to infest the millet and were mixed 1:1 prior to inoculation. Holes were made 1 cm from the plant crown and 2 g of millet was inserted. Fungicides were applied using a CO2 backpack sprayer for soil drench applications (100 ml/plant) using a single-nozzle boom with one 8006EVS nozzle calibrated at 35 psi to deliver 100 gal/A. Foliar applications were applied using a CO2 backpack sprayer with three XR8003 flat fan nozzles spaced 18 in apart calibrated at 35 psi to deliver 50 gal/A. Fungicides were applied on 20, 27, 30 Jun and 7, 11, 18 Jul for the 7-day interval treatments. Fungicide treatments were applied on 20, 30 Jun and 11, 25 Jul for 14-day interval treatments. Dead plants were counted on 18, 25, 31 Jul and 7 Aug and the percentage of dead plants was calculated by dividing the number of dead plants by the total number of plants in a plot (10) and multiplying by 100. The area under the disease progress curve (AUDPC) was calculated using the percentage of dead plants. Data were analyzed using an analysis of variance using (ANOVA) SAS PROC GLIMMIX procedure of the SAS software version 9.4 (SAS Institute, Cary, NC), with mean separation performed using Fisher’s protected least significant difference (LSD) at P<0.05.

Disease pressure was relatively low (<28% of plat death in all treatments) at the initial rating date on 18 Jul, and no statistical differences (P=0.1438) were observed among the treatments. On the following evaluation date, 25 Jul, the untreated control reached 77.5% plant death. All the treatments expressed significantly (P=0.0144) lower (<35.0 %) percent of plant death than the untreated control. Presidio 4 fl oz expressed the lowest percent of plant death of the treatments evaluated. However, the rest of the treatments were statistically (P=0.0144) similar to Presidio 4 fl oz except Funibiol Gold 32 fl oz and Theia 1.5 lb. + Howler EVO 2.5 lb. Funibiol Gold 32 fl oz and Theia 1.5 lb + Howler EVO 2.5 lb were significantly better than the untreated control and similar to each other at the second rating date. On the final rating date, the untreated control developed 97.5 % of plant death. All treatments statistically (P=0.0249) reduced plant death compared to the untreated control on the final rating date, except Theia 1.5 lb. Theia 1.5 lb. was similar to the untreated control and all other fungicide treatments; all the treatments were similar for plant death on the final rating date. According to the area under the disease progress curve (AUDPC), all treatments had significantly (P=0.0008) less disease than the untreated control. Presidio 4 fl oz had the lowest AUDPC but was similar to all other fungicide treatments except Theia 1.5 lb. and Theia 1.5 lb. plus Howler EVO 2.5 lb. When combined with host resistance, Biorational could efficiently manage Phytophthora crown rot.

4.2.2 Evaluation of integrated disease management in cucurbits combining host resistance and chemical control (Year 3-4).

Watermelon Fusarium wilt

(Lead: Schultheis, Secondary Site: Keinath):

Schultheis, Keinath (2023):

Triploid watermelon cultivars ‘Fascination’ and ‘Eleanor’ were evaluated for disease incidence and yield when treated with one of three fungicide programs (prothioconazole (Proline), prothioconazole + fluopyram (Propulse), Proline and Propulse) while growing in fields infested with Fusarium oxysporum f. sp. niveum. ‘Fascination’, ‘Eleanor’, and ‘Shoreline’ also were evaluated for disease incidence and yield in grafted (G) and un-grafted (UG) (control) treatments. The study was conducted at two locations at research stations in Clinton, NC, and Charleston, SC, and used a randomized complete block design with four replications. Transplants were established on 3 May 2023 in NC and on 5 April 2023 in SC. Ten triploid plants made up each plot in NC and 12 plants in SC. Four pollenizers, SP-7 and G SP-7, were used per plot. Disease incidence was rated for eight weeks starting on 24 May 2023 in NC and on 25 April 2023 in SC. Proline at 5.7 oz/ac and Propulse at 13.6 oz/ac was applied to the corresponding plots via drip irrigation the day after transplanting. An additional drip application of Proline was applied to the plots receiving the Proline and Propulse treatment 15 days after transplanting. Yield data were collected over 4 harvests in NC from 20 July to 11 August 2023. In SC, yield data were collected over 8 harvests from 19 June to 7 August 2023. G ‘Fascination’, ‘Eleanor’, and ‘Shoreline’ had the lowest disease incidence at both locations with ≤0.6% incidence. Un-grafted ‘Shoreline’ had the highest disease incidence 11 weeks after transplanting at both locations with ≥95.0% incidence. The three G treatments had the highest yields at both locations and produced ≥34,317 lb/ac in NC and ≥33,832 lb/a in SC. In NC the three G treatments yielded higher than all other treatments. . Ungrafted ‘Shoreline’ had the lowest yields at both locations with 0 lb/ac in NC and 916 lb/ac in SC. In this study, grafting was a more effective management option than fungicides against Fusarium wilt of seedless watermelon

Cucumber downy mildew

(Lead: Hausbeck, Secondary Site: Quesada):

Quesada (2023):

The experiment was performed at the Horticultural Crops Research Station in Clinton, NC. Experimental plots were single raised beds on 5-ft centers covered with white plastic mulch; 14-ft long with 5-ft fallow borders on each end and non-treated guard rows on each side. Susceptible pickling cucumber ‘Vlasik’ and two tolerant pickling cucumber cultivars, ‘Citadel’ and ‘Chaperon’, were directly seeded on 2 Aug (2-ft in-row spacing, 2 seed/hill) and thinned to one plant per hill after emergence (7 plants/plot). Regular cultural practices like irrigation and fertilization (4-0-8, N-P-K) were applied via drip tape. Three chemical program treatments and non-treated control were tested in a factorial design with each cultivar in a randomized complete block design with four repetitions. Fungicide treatments were applied using a CO2-pressurized backpack sprayer equipped with a single-nozzle, handheld boom with a hollow cone nozzle (TXVS-26) delivering 40 gal/A at 35 psi on Aug 30, Sep 6, Sep 15, Sep 20, Sep 27 and Oct 4. Disease severity per plot was assessed every week. Yields were assessed every week (3 data points) as marketable and non-marketable (summarized as total marketable and total non-marketable). Data were analyzed in the software ARM (Gylling Data Management, Brookings, SD) using analysis of variance (AOV) and Fisher’s protected least significant differences (LSD) test to separate means.

Downy mildew was first detected on 30 Aug at approximately 2% disease severity in the field. No phytotoxicity was observed for any treatments in the experiment. Only 6 foliar applications were able to be applied because disease at the end of the trial reached 100%, and the trial was concluded. Disease severity in the non-treated ‘Vlaspik’ and ‘Citadel’ plots were significantly different from ‘Chaperon’ non-treated plots. Area under disease progress curve values were significantly different across each variety and varied by fungicide program for each variety. Marketable yields were variable across treatment, with ‘Chaperon’ Howler Evo+Dyne-Amic+Kocide+Dyne-Amic+Citadel producing 21.20 lbs/treatment and ‘Vlaspik’ Howler Evo+Dyne-Amic+Kocide+Dyne-Amic+Citadel producing 10.28 lbs/treatment.

Table: Disease Severity and Marketable Yields of Cucumber varieties

Hausbeck (2023): The experiment was established at the Michigan State University Southwest Michigan Research and Extension Center near Benton Harbor, MI, in sandy soil previously planted to cucurbits. The field was plowed and disced, and pre-plant fertilizer (180 lb/A potassium, 25 lb/A sulfur, and 2.0 lb/A boron) was applied and incorporated on 19 May. On 26 May, raised beds were formed in the field with black plastic mulch 8 ft apart with drip tape for irrigation and in-season fertilization. Biweekly mechanical cultivation and hand weeding were used for weed control. Planting occurred on 25 Jul from seed. The cultivars used for this experiment were cucurbit downy mildew (CDM) susceptible ‘Vlaspik’ and CDM intermediately resistant ‘Citadel’ and ‘Chaperon’. Three fungicide programs, including a standard program, a mix of standard and an organic program, and an organic program, were compared to an untreated control in this trial. The treatments were arranged in a split-plot design with the fungicide program nested within the cultivar and four replications. Each replicate row was 20 ft long with a 5 ft buffer between each plot in a row. In-season fertilization occurred with applications of urea ammonium nitrate (1.0 gal/A/day) through the drip tape daily. Fungicide treatments were applied using a CO2 backpack sprayer and a broadcast boom equipped with three XR8003 flat-fan nozzles spaced 18 in apart, calibrated at 35 psi, and delivering 50 gal/A. Fungicide applications occurred on 7, 14, 23 and 28 Aug; 5, 15 and 19 Sep. The percent of disease severity was visually assessed using a 0-100 scale on 23 and 30 Aug; 8, 11, 21, and 28 Sep. Mature fruits were harvested on 15 and 21 Sep. Data were analyzed using an analysis of variance using (ANOVA) SAS PROC GLIMMIX procedure of the SAS system 9.4 (SAS Institute, Cary, NC). Least-square means comparisons were performed using Tukey’s honestly significant difference test (HSD P<0.05). According to ANOVA, significance (HSD P<0.05) was detected for cultivars, programs, and the interaction of cultivar*program. According to marginal means within cultivars, the cultivars ‘Citadel’ and ‘Chaperon’ developed statistically (HSD P<0.05) less disease severity than ‘Vlaspik’ during the evaluation period as well as the AUDPC, while ‘Citadel’ and ‘Chaperon’ were statistically similar (HSD P<0.05) for disease severity and AUDPC. According to the program’s marginal means, all the programs statistically limited (HSD P<0.05) disease severity and AUDPC compared to the untreated control except for the organic program (Howler EVO 2.5 lb plus Dyne-Amic 0.375% V/V alternated with Kocide 1.25 lb plus Dyne-Amic 0.375% V/V). The mixed program (Orondis Opti 2.5 pt + Kocide 1.25 lb, alternating with Ranman + Howler EVO 2.5 lb + Dyne-Amic 0.375% V/V, alternated with Previcur Flex 1.2 pt + Kocide 1.15 lb + Dyne-Amic 0.375% V/V alternated with Zampro 14 fl oz + Howler EVO 2.5 lb + Dyne-Amic 0.375% V/V) and the standard program (Orondis Opti 2.5 pt alternated with Ranman 2.75 fl oz + Bravo WeatherStik 2 pt alternated with Previcur Flex 1.2 pt + Bravo WeatherStik 2 pt alternated with Zampro 14 fl oz plus Bravo WeatherStik 2 pt) similarly limited the disease infection. By observing the simple effect of the fungicide programs sliced by cultivars, ‘Vlaspik’ plants significantly (HSD P<0.05) have less disease when sprayed with the mixed and standard program (6.3% and 1.3% of disease severity) than those plants left untreated or sprayed with the organic program (81.3% and 71.3% of disease severity) at final rating date and the AUDPC. The disease pressure was consistently lower in the ‘Citadel’ plants than in ‘Vlaspik’ plants regardless of the treatment sprayed. Non-statistical differences were observed when ‘Citadel’ plants were untreated or treated with the programs at the final rating day (0% to 12.5 % of disease severity). According to the AUDPC, the mixed and standard programs had a lower AUDPC than the untreated control and the organic programs. The organic program had a similar AUDPC than the untreated control. Disease pressure on ‘Chaperon’ plants was the lowest of all the cultivars tested; all programs tested were similar to the untreated control at the final rating date (0.0 % to 3.8 % of disease severity) and AUDPC. There was no interaction for harvest data, and no differences were observed among treatments for yield. In Michigan, the management of cucurbit downy mildew could be improved by combining genetic resistance and fungicides.

Table: Foliar Disease severity of Cucumbers

Table: Foliar Disease Severity of Cucumbers with different treatment programs

Squash powdery mildew

(Lead: Smart, Secondary Site: Hausbeck):

Smart (2021, 2022):

Year 1: Smart conducted a field trial evaluating 9 biofungicides to control powdery
mildew. Kocide 3000-O (Certis) was the most effective at reducing powdery mildew severity followed by
Theia (AgBiome), compared to the untreated control.

Year 2: Field trial evaluating 11 biorational fungicides (two copper products and ten biologicals) to control powdery mildew. Kocide 3000-O was again the most effective at reducing disease severity, followed by Theia, Dyne-Amic (Helena Agri), and Curezin (VM Agritech), compared to the untreated control.

Hausbeck (2022):

A trial was established at the Michigan State University Plant Pathology Farm in East Lansing, MI, in a field of Capac loam soil previously planted to pumpkin. The field was plowed on 20 May and disced 1-June. Preplant fertilizer (80 lb. per acre N and 105 lb. per acre of K) was applied and incorporated on 1-June. On 2-June, raised beds were formed in the field with black plastic mulch 12 ft apart, and drip tape (0.65 gpm/100 ft) for irrigation and in-season fertilization. Biweekly mechanical cultivation and hand weeding was used for weed control. Planting occurred 13-June via transplanting. The cultivar used for this experiment was ‘Tiptop’ which has intermediate resistance to powdery mildew. The treatments were arranged in a completely randomized block design with four replications. Each replication was 20 ft with a 5 ft buffer between each plot in a row. Each week during the growing season the trial was fertilized with 28% N liquid fertilizer at 1 gal per acre through the drip tape. Presidio (4 fl oz/A) was applied on 21-July. For control of Phytophthora crown rot, Admire Pro was applied through the drip lines on 20-June. for insect control. Spray treatments were applied on 29-July and 5-, 12-, 19-, 26-Aug. using a CO2 backpack sprayer and a broadcast boom equipped with four XR8003 flat-fan nozzles spaced 18 in. apart, calibrated at 35 psi and delivering 50 gal/A. Foliage was evaluated for infection (%) (both upper and lower side) on 18-, 24-, 29-Aug. and for necrosis on 5-Sep. Area under the disease progress curve was calculated using foliar infection for the upper side of the leaf and using foliar infection for the lower side of the leaf. Area under the disease progress curve was calculated using foliar infection for the upper side of the leaf and using foliar infection for the lower side of the leaf. Disease on the lower side of the leaf progressed from 3.8% (18-Aug.) to 51.3% (29-Aug.) in the untreated control. A significant increase in disease occurred for all treatments between 18- and 24-August. On 24- August, all treatments had significantly less disease than the untreated control. On the final rating date (29-Aug.), all treatments differed from the untreated control except MBI-121 and Theia + Activator 90 alternated with Microthiol Disperss. According to the area under the disease progress curve (AUDPC), all treatments differed from the untreated control but not each other. Disease on the upper side of the leaf progressed from 2% (18-Aug.) to 45% (29-Aug.) over the course of the trial. According to disease severity on the final rating date (29-Aug.) and AUDPC only treatments that included Microthiol Disperss differed from the untreated control. According to foliar necrosis on 5-Sep., all treatments differed from the untreated control except Trillium and treatments containing Microthiol Disperss had less necrosis overall. No phytotoxicity was observed. In general, programs with either Microthiol Disperss alone or in a program were the only treatments that consistently limited powdery mildew disease progress in our study.

Table: Foliar infection on lower leaf surface

Table: Foliar infection on upper leaf surface

Hausbeck (2023):

The trial was established at the Michigan State University Plant Pathology Farm in Lansing, MI, in a field of Capac loam soil previously planted to squash. The field was plowed on 9 May and disced 15 May. Preplant fertilizer (130 lb/A urea and 130 lb/A potash) was applied and incorporated on 16 May. On 17 May, raised beds were formed in the field with black plastic mulch 12-ft apart with drip tape for irrigation and in-season fertilization. Biweekly mechanical cultivation and hand weeding was used for weed control. Planting occurred 31 May via transplanting Unsing three weeks olds seedlings. The cultivar used for this experiment was intermediately resistant ‘Tiptop’. The treatments were arranged in a randomized complete block design with four replications. Each replication was 20 ft long with a 5-ft buffer between each plot in a row. Each week during the growing season the trial was fertilized with urea ammonium nitrate (28% N) at 1 gal/A through the drip tape. Admire Pro SC (10.5 fl oz/A) was applied through the drip tape on 5 and 24 Jul and Warrior CS (1.92 fl oz/A) was sprayed on 28 Jul for insect control. Spray treatments were applied on 19 and 27 Jul; 2, 9, 16, 24 and 31 Aug; and 7 Sep using a CO2 backpack sprayer and a broadcast boom equipped with four XR8003 flat-fan nozzles spaced 18 in. apart, calibrated at 35 psi, and delivering 50 gal/A. Foliage was evaluated for disease severity (both upper and lower surface of the leaf) on 3, 14, 24 and 30 Aug; 7 and 14 Sep and for necrosis on 24 and 30 Aug; 7 and 14 Sep. Evaluations were conducted using a 0 to 100 % scale, with 0% = 0% foliar disease/necrosis and 100% = 100% foliar disease/necrosis. Area under the disease progress curve was calculated for the upper and lower leave surface and for necrosis using disease severity data. Data were analyzed using an analysis of variance (ANOVA) with means separation performed using Fisher’s protected least significant difference (LSD). According to disease severity on the final rating date, there were no differences among treatments for either the upper or lower leaf surfaces. On the upper leaf surface, all treatments limited the area under the disease progress curve (AUDPC) compared to the untreated control except for Zonix L 500 ppm plus Kinetic L 6 oz/100 gal. No differences among treatments were observed for AUDPC on the lower leaf surface. According to the foliar disease severity on the final rating date, only treatments that included SilMatrix 3 qt./ 100 gal limited necrosis compared to the untreated control. According to AUDPC, only Zonix L 500 ppm plus Sil-Matrix SC 3 qt./ 100 gal had less disease than the untreated control.

Table: Foliar Disease Severity on the Upper Leaf Surface

Smart (2023):

One trial evaluating the effectiveness of integrating breeding lines with biorational fungicides to manage powdery mildew (PM): There were 2 lines and 1 susceptible control, and 3 fungicides with 1 untreated control. Fungicides included Curezin (copper zinc), Kocide 3000-O (copper hydroxide), and Theia (Bacillus subtilis). One breeding line, TR2-03, consistently had the least disease, regardless of fungicide treatment. Within breeding lines, we found no impact of PM severity on yield. The susceptible control yielded significantly more fruit weight per plot than the other lines. However, the susceptible control was no different than TR2-06 in fruit number per plot. TR2-03 yielded significantly less than both the susceptible control and TR2-06 in both fruit number and weight per plot. We conclude that, of the products evaluated, host resistance played a larger role than fungicides in reducing PM. One trial evaluating the canning quality of processing pumpkin breeding lines: There were 2 lines, plus both parents, ‘Dickinson’ and ‘Bugle’. ‘Bugle’ is a powdery mildew-resistant butternut squash, and ‘Dickinson’ is a standard processing cultivar. Fruit from each line fruit were puréed, canned, and compared to both parents, with assessments including moisture content (%), ˚Brix, pH, consistency, and color. Purées from the two breeding lines were more similar to ‘Dickinson’ than ‘Bugle’.

Squash Phytophthora blight

(Lead: Hausbeck, Secondary Site: Smart):

Hausbeck (2022):

A study was conducted at the Michigan State University Southwest Research and Extension Center located near Benton Harbor, MI on sandy soil previously planted to squash. Preplant fertilizer (nitrogen 100 lb./A, potassium 180 lb./A, sulfur 25 lb./A, and boron 2.0 lb./A) was applied on 31 May. On 7-June 3-week-old ‘Enterprise’ summer squash plants were transplanted 18 in. apart into 6-in. raised plant beds covered with black polyethylene plastic and spaced 8 ft apart. A single drip tape (0.65 gpm/100 ft) was installed under the plastic mulch for plot irrigation. Fertilizer (nitrogen 28%) was applied weekly at a rate of 1 gal/A through the drip irrigation. For each treatment, a replicate consisted of a single 20-ft row with a 5-ft buffer within the row to separate treatments. Treatments were arranged in a randomized block design with four replicates. On 5-July, plants were inoculated with P. capsici-infested millet (100 g sterilized millet, 72 ml distilled water, 0.08 g asparagine, and seven 7-mm plugs of P. capsici). P. capsici isolates 12889 (A1 mating type, sensitive to mefenoxam, isolated from cucumber) and SP98 (A2 mating type, sensitive to mefenoxam, isolated from pumpkin) were used to infest the millet and were mixed 1:1 prior to inoculation. Holes were made 1 cm from the plant crown and 1 g of millet was inserted. Fungicides were applied with a CO2 backpack sprayer as a soil drench (100 ml/plant) using a hand-wand without nozzle at 20 psi. Fungicide treatments were applied on 1-, 8-, 15-, and 22- July. Dead plants were counted on 19-, 22-, 26-, 29-Jul., and 2 August. Data were analyzed using an analysis of variance (ANOVA), with mean separation performed using Fisher’s Protected Least Significant Difference (LSD).

The percentage of dead plants progressed over the course of the study from 30.8% to 75% for the untreated control plots from 19 July to 2 August. Differences among treatments were not observed on 19- July. Presidio SL was the most effective treatment with <10% dead plants on the last rating date (2-Aug), significantly less than Double Nickel LC treatment but not significantly different from the remaining treatments. Mega 128, Rootshield Plus WP, MGCI Phytalix, and Double Nickel LC did not differ significantly from the untreated control (p≤0.05). The AUDPC data indicated that Presidio SL was the only effective product and that Mega 128, Rootshield Plus WP, MGCI Phytalix, and Double Nickel LC were the least effective products for controlling Phytophthora crown rot in 2022.

Table: Percent Squash Plant Death

Smart (2022):

The identical trial to that of Hausbeck in MI was conducted in NY. We tested product efficacy against Phytophthora capsici on squash. The experiment included 4 biofungicides, 1 conventional fungicide (Ridomil) and an untreated control (exactly as described above by Hausbeck). Plants were inoculated on August 4, 2022 using Phytophthora capsici growing in vermiculite. One gram (about 1 teaspoon) of inoculum was buried 1 centimeter from the crown of each plant. To determine the zoospore concentration of the inoculum, we placed one gram in 100 ml of water (repeated three times) and used a hemacytometer to determine the number of zoospores per one gram of inoculum. This was 2 x 106 zoospores per one gram of inoculum. Plants were rated 6 times. Only Ridomil was effective in reducing disease in the NY trial. Plants in all treatments other than Ridomil died within two weeks of inoculation.

Hausbeck (2023):

This study was conducted at the Michigan State University Southwest Research and Extension Center located near Benton Harbor, MI on sandy soil previously planted to squash. The field was plowed, disced, and preplant fertilizer (potassium 180 lb/A, sulfur 25 lb/A, and boron 2.0 lb/A) was applied on 19 May. On 26 May, 6-in. raised plant beds covered with black polyethylene plastic were laid spaced 16 ft apart. A single drip tape (0.65 gpm/100 ft) was installed under the plastic mulch for plot irrigation. On 2 Jun, 3-week-old ‘Thunder’ winter squash plants were transplanted 18 in. apart. Fertilizer (urea ammonium nitrate 28% N) was applied weekly at a rate of 1 gal/A/day through the drip tape. For each treatment, a replicate consisted of a single 20-ft row with a 5-ft buffer within the row to separate treatments. Treatments were arranged in a randomized complete block design with four replicates. On 23 Jun, plants were inoculated with P. capsici-infested millet (100 g sterilized millet, 72 ml distilled water, 0.08 g asparagine, and 7 7-mm plugs of P. capsici). P. capsici isolates 12889 (A1 mating type, sensitive to mefenoxam, isolated from cucumber) and SP98 (A2 mating type, sensitive to mefenoxam, isolated from pumpkin) were used to infest the millet and were mixed 1:1 prior to inoculation. Holes were made 1 cm from the plant crown and 2 g of millet was inserted. Fungicides were applied using a CO2 backpack sprayer for soil drench applications (100 ml/plant) using a single-nozzle boom with one 8006EVS nozzle calibrated at 35 psi to deliver 100 gal/A. Foliar applications were applied using a CO2 backpack sprayer with three XR8003 flat-fan nozzles spaced 18 in apart calibrated at 35 psi to deliver 50 gal/A. Fungicides were applied on 20, 27, 30 Jun and 7, 11, 18 Jul for the 7-day interval treatments. Fungicide treatments were applied on 20, 30 Jun and 11, 25 Jul for 14-day interval treatments. Dead plants were counted on 18, 25, 31 Jul and 7 Aug and the percentage of dead plants was calculated by dividing the number of dead plants by the total number of plants in a plot (10) and multiplying by 100. The area under the disease progress curve (AUDPC) was calculated using the percentage of dead plants. Data were analyzed using an analysis of variance using (ANOVA) SAS PROC GLIMMIX procedure of the SAS software version 9.4 (SAS Institute, Cary, NC), with mean separation performed using Fisher’s protected least significant difference (LSD) at P<0.05.

Table: Percent Squash Plant Death

4.2.3 Analysis of pathogen populations to inform breeding and disease management (Year 2-3).

Phytophthora capsici (Smart):

We now have a panel of about 120 isolates of P. capsici for which we have genotype data, using genotyping-by-sequencing, to identify a SNP panel of over 64,000 SNPs. For this same panel, we have phenotypic data including pathogenicity on cucurbits and pepper as well as sensitivity to the fungicide mefenoxam, and mating type for each of these isolates. Using a genome-wide association study, we were able to map the gene that is likely responsible for resistance to the fungicide mefenoxam, and identified a potential effector that is recognized by a subset of host plants. During the 2022 field season, we collected 121 additional isolates from western New York and 69 isolates from California. We are currently completing single zoospore isolation from each of these isolates, and genotyping will begin in the near future. During the 2023 field season we plan to get additional isolates from states including North Carolina, South Carolina, and potentially Michigan, Georgia or Tennessee. These isolates will be included in our genotyping and phenotyping studies and used in GWAS to map traits of interest.

Collection of Phytophthora capsici isolates for population study:

26 isolates were collected in New York. In 2024, a total of 248 isolates collected between 2022-2023 will be genotyped. These isolates comprise populations from California, New York, and North Carolina, and were collected from Cucurbita moschata, C. pepo, and pepper. Additionally, fungicide insensitivity (mefenoxam) was observed in approximately 40% of the 248 isolates.

The above work is a follow-up to the work a previous student, Greg Vogel, had done as part of CucCAP2 looking at differences in virulence, and presumably effector composition, of 118 isolates. This work was presented to the CucCAP2 team in March 2023.

Pseudoperonospora cubensis (Quesada):

Since its reemergence in 2004, Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew (CDM), has experienced significant changes in fungicide sensitivity. Presently, frequent fungicide applications are required to control the disease in cucumber due to the loss of host resistance. Carboxylic acid amides (CAA) and quinone outside inhibitors (QoI) are two fungicide groups used to control foliar diseases in cucurbits, including CDM. Resistance to these fungicides is associated with single nucleotide polymorphism (SNP) mutations. In this study, we used population analyses to determine the occurrence of fungicide resistance mutations to CAA and QoI fungicides in host-adapted clade 1 and clade 2 P. cubensis isolates. Our results revealed that CAAresistant genotypes occurred more prominently in clade 2 isolates, with more sensitive genotypes observed in clade 1 isolates, while QoI resistance was widespread across isolates from both clades. We also determined that wild cucurbits can serve as reservoirs for P. cubensis isolates containing fungicide resistance alleles. Finally, we report that the G1105W substitution associated with CAA resistance was more prominent within clade 2 P. cubensis isolates while the G1105V resistance substitution and sensitivity genotypes were more prominent in clade 1 isolates. Our findings of clade-specific occurrence of fungicide resistance mutations highlight the importance of understanding the population dynamics of P. cubensis clades by crop and region to design effective fungicide programs and establish accurate baseline sensitivity to active ingredients in P. cubensis populations.

4.3. Economic impacts of disease and gains from control tools and valuation of crop attributes (Year 1-4). (Tregeagle)

4.3.1. Determine economic impacts of disease and control tools (Year 1-4).
Cucumber production costs were collected from participants at the SE Vegetable & Fruit Expo
4.3.2 Estimate industry valuation of improvement in crop attributes (Year 1-4).
Draft evaluation surveys were prepared for cucumbers, watermelon, summer squash, and winter squash. Drafts were shared with members of the CucCAP2 team and the stakeholder advisory board. Comments were received and incorporated.
Cucumber survey was launched online and data collection is ongoing.