Integrated Crop and Disease Management Team | 2023 Progress Report

cuccap

View Tables and Figures in the PDF version of the 2023 CucCAP Integrated Disease Mangement Team Report.

Project Personnel

  • Lina Quesada-Ocampo (NC State)
    Yara Rosado (technician), Mary Lorscheider (extension communicator), Mariana Prieto (PhD student), Andres Salcedo (Postdoc), Ziaur Bhuyian (Postdoc)
  • Mary Hausbeck (MSU)
    Carmen M. Medina-Mora (technician), Matthew Uebbing (graduate student), David Perla (graduate student), Chris Smart (Cornell), Colin Day (lab manager), Taylere Herrmann (technician), Libby Indermaur (PhD student), Emma Nelson (PhD student), Janna Fladd (high school intern)
  • 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), Andrew Pfefferkorn (Technical Support), Kaleb Holder (Technical Support)
  • Daniel Tregeagle (NC State)
    Alice Kilduff (PhD Student)

Perform multi-location, multi-isolate trials to improve integrated disease management, assess economic impacts, and provide state-of-the art disease control recommendations

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

  • CucCAP website: From Sept. 1, 2021 until Feb. 7, 2023, the CucCAP website was visited by
    24,933 users including 24,707 new users with 29,720 sessions and 48,432 pageviews. A total of 158 news items were posted on the website including 57 posts of news from CucCAP researchers and 112 crop and disease reports. These posts were shared in a monthly newsletter sent to 160 subscribers and in 125 posts on social media including Facebook with 168 followers, Twitter with 130 followers, and LinkedIn with 18 followers. Cucurbit disease factsheets and links to integrated pest management resources are maintained and updated annually on the website. Five of the top ten pages visited on the website were Cucurbit disease management factsheets in Spanish. The CucCAP website events calendar shared notices of 10 regional commodity meetings, 22 education sessions, and 22 Scientific meetings.
  • Quesada: Since the start of the project, Quesada has provided diagnostics and disease management recommendations for 28 cucumber, 52 watermelon, 12 melon, 16 squash, and 12 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: 6,578 (lab) + 3,762 (Quesada) followers, LinkedIn: 2,869 followers), and generating disease management resources such as the NC Agricultural and Chemicals Manual and the Southeastern US Vegetable Crop Handbook.
    Smart: Smart has provided diagnostics and disease management recommendations for cucumber, melon, squash, and pumpkin samples received across New York State (n=47). The Smart lab has also provided disease management recommendations through oral presentations, extension publications, and social media (Twitter: 2,088 followers, @ChristineSmart6).
  • Hausbeck: Hausbeck maintains a page dedicated to downy mildew (Downy Mildew
    News), which gets frequently updated during the cucurbits growing season (late May to late Sept.) maintaining the scientific community and growers informed with current information about the disease. This page includes a weekly summary of the results from spore trapping used for tracking, monitoring, and forecasting the disease in the state. This year’s results corresponded to seven spore traps deployed in counties with commercial production of cucurbits along Michigan’s lower peninsula. In addition, the webpage includes a Michigan map updated daily as mildew symptoms are confirmed in the state, facts sheets, illustrative identification of mildew on cucurbits, and reference articles and links to main diseases threatening crop production of cucurbits.
  • Schultheis: Since the start of the project, Schultheis has been involved in cultivar evaluations on melon, zucchini, pumpkin, and watermelon. Watermelon cultivar response to Fusarium wilt has been the main focus and this information has been conveyed through oral and poster presentations.

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

Watermelon powdery mildew (Lead: Kousik, Secondary Site: Quesada):

  • Kousik: 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=612%, 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 USVL608PMR 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: 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: 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 inrow 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: 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: 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: 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 (MSUPPF) 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: 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: 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: 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: 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.

Squash Phytophthora blight (Lead: Hausbeck, Secondary Site: Smart):

  • Hausbeck: 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; 22T1B-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 (22T1B-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-T1B04, 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.
    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’).
    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.
  • Smart – 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.

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 and Keinath have not started with this activity since it is planned for years 3 and 4.

Cucumber downy mildew (Lead: Hausbeck, Secondary Site: Quesada): Quesada has not started with this activity since it is planned for years 3 and 4.

  • Hausbeck:  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 cucumber. The field was plowed on 20 May and disced 1 June. Preplant fertilizer (220 lb./A urea and 180 lb./A potash) was applied and incorporated on 1 June. On 9 July, raised beds were formed in the field with black plastic mulch 8-ft apart, and drip tape for irrigation and in-season fertilization. Biweekly mechanical cultivation and hand weeding was used for weed control. Planting occurred on 26 July from seed. The cultivar used for this experiment was ‘Citadel’. The treatments were arranged in a completely randomized block design with four replications. Each replicate was 20ft 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/A through the drip tape. Quadris F (15.5 fl oz/A) and Torino SC (3.4 fl oz/A) were sprayed on 26 August to control the incidence of Alternaria spp and powdery mildew and Admire Pro (10.5 fl oz/A) was applied on 10 August through the drip lines for insect control. Spray treatments were applied on 16 and 23 August 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. Foliage was evaluated for infection on 18, 24, and 29 August by visually estimating the area of foliage with symptoms (%). Data were analyzed using an analysis of variance (ANOVA) with means separation performed using Fisher’s protected least significant difference (LSD).
    Disease severity in the untreated control progressed from 10% on 18 August to 25% on 29
    August. A significant increase in disease occurred from 18 August to 24 August in all treatments. There were no statistical differences among treatments at any of the rating dates, though Trillium had numerically less disease (17.5%) compared to all other treatments (21.3-26.3%) on the final rating date (29 August). According to the area under the disease progress curve (AUDPC), no treatment differed from the untreated control. Trillium did have significantly less disease compared to Kocide and MBI-121 alternated with Kocide. No phytotoxicity or tank mix incompatibilities were observed during the duration of the trial.

Squash powdery mildew (Lead: Smart, Secondary Site: Hausbeck)

  • Smart : 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. Year 3-4: Smart will conduct an integrated trial with three squash cultivars and Kocide 3000-O, Theia, and Curezin.
  • Hausbeck: 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-, 26Aug. 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 MBI121 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% (29Aug.) 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.

Squash Phytophthora blight (Lead: Hausbeck, Secondary Site: Smart):

  • Hausbeck: 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.
  • Smart: 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.

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.
  • 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 CAA-resistant 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.

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

Determine economic impacts of disease and control tools (Year 1-4).

A draft pickling cucumber budget for North Carolina has been prepared. The remaining budgets will be prepared in 2023. Economic impact analysis will be conducted in 2024, combining the prepared budgets and the results of the other PIs field trials.

Estimate industry valuation of improvement in crop attributes (Year 1-4).

The literature regarding vegetable producer willingness-to-pay for crop traits was reviewed by Tregeagle and team, who performed a meta-regression analysis on existing estimates of producer willingness-to-pay for crop traits, comparing these results to existing consumer estimates. This analysis confirmed that estimates for producer willingness-to-pay for cucurbits are not available in the current literature, but that, in general, producers are willing to pay a premium for diseaseresistant varieties.

Techniques identified in the existing literature are being adapted to develop surveys for the three crop-pest pairs below. The cucumber/downy mildew survey has been the focus of development, being used as a test case to refine the survey contents, distribution methods, and statistical design, which will then be applied to the other crop-pest pairs.

  • MI – cucumber/downy mildew (Hausbeck): The cucumber-downy mildew survey and related materials are currently being prepared for submission to NC State’s IRB for review – the final step before deployment of the survey.
  • MI – squash/phytophthora (Hausbeck): Draft attributes and levels for squash/phytophthora survey have been developed from a review of current seed catalogs published by a variety of commercial seed distributors. The draft attributes and levels will be refined by discussions with other PIs and industry members, preparing the survey for deployment in 2023/2024.
  • NC – cucumber/downy mildew (Quesada): Quesada and Tregeagle have met several times to collaboratively develop this survey. However, the pandemic has delayed survey efforts due to cancellation of many extension events and grower meetings. We have plans to deploy this during inperson grower events in 2023. The cucumber-downy mildew survey and related materials are currently being prepared for submission to NC State’s IRB for review – the final step before deployment of the survey.
  • NC – watermelon/fusarium (Schultheis): Draft attributes and levels for watermelon/fusarium survey have been developed from a review of current seed catalogs published by a variety of commercial seed distributors. The draft attributes and levels will be refined by discussions with other PIs and industry members, preparing the survey for deployment in 2023/2024. Schultheis and Tregeagle have met several times to discuss the design of the survey.
  • NY – squash/phytophthora (Smart): Smart has collected data on the value of winter squash in NY from producers and field scouts. The average price for winter squash in NY is $31.00 per cwt. Average yield in NY is 12 Tons/A with yields in 2022 ranging from 8-20 Tons/A. Average loss per year due to Phytophthora is 10%. In wet years losses will be higher, up to 35% (of total acreage) which would be 80-100% in some fields and 0-20% in other fields.
  • Draft attributes and levels for squash/phytophthora survey have been developed from a review of current seed catalogs published by a variety of commercial seed distributors. The draft attributes and levels will be refined by discussions with other PIs and industry members, preparing the survey for deployment in 2023/2024.
  • SC – watermelon/fusarium (Keinath): Draft attributes and levels for watermelon/fusarium survey have been developed from a review of current seed catalogs published by a variety of commercial seed distributors. The draft attributes and levels will be refined by discussions with other PIs and industry members, preparing the survey for deployment in 2023/2024.