With the wet conditions experienced across most of southern Ontario over the past few weeks, the risk of both foliar and root diseases is high on many specialty crops. There is a particularly high risk of diseases caused by water moulds such as downy mildew and Phytophthora. These include basil downy mildew, hops downy mildew, cucurbit downy mildew, and late blight (Phytophthora) on specialty crops related to tomato and potato. Hops and cucurbit downy mildews have been reported in Ontario, and basil downy mildew is spreading north up the eastern seaboard of the US. There have been no reports of late blight in Ontario in either tomatoes or potatoes so far. If products are available, growers should ensure protection of the crop from these diseases before symptoms first appear, and continue rotating available options until weather conditions become less conducive to disease. Management of these diseases requires regular scouting to catch the disease before it becomes widespread. Once the diseases become widespread in a field they can be very difficult to control. If you suspect you have one of these diseases in your crop, please contact an OMAF and MRA specialist.
Most other diseases are promoted by wet conditions and/or high humidity including leaf spots and blights (e.g. Alternaria, Septoria), powdery mildew, various crown and root rots, and bacterial diseases. With these diseases, scouting and preventative application of pest control products will also be the key to control.