Downy mildew, caused by the oomycete Pseudoperonospora cubensis, has been reported in watermelon in North Carolina. It was observed in Nash county (June 17, 2016) and the field presented 5% incidence with each infected plant/leaf having 50% severity. A recent report from Johnston county (June 23, 2016) was from a watermelon field with 5% incidence and 30% severity. A previous report earlier this month (June 1st, 2016) was on cucumber in Duplin county.
Source: Watermelon downy mildew reported in North Carolina | North Carolina Cooperative Extension