This serious disease of vine crops has long been a problem in the Northern US, including New York and Michigan. Here in Ontario, while it has been identified sporadically, we have been fortunate to escape the severe infections experienced south of the border.

Phytophthora symptoms can include stunting, crown rot and fruit rot depending on the crop species and the time of infection. The crown rot phase is the most destructive. Dark-green lesions form on the crown, girdling it and causing the entire plant to turn yellow/brown and die. Fruit infections begin as a large water-soaked lesion. Under humid conditions, a thin layer of white spores develop on the surface of the fruit. These spores resemble a fine dusting of powdered sugar.

Figure 1. Phytophthora Fruit Rot - Zucchin

Figure 2. Phytophthora Crown Rot - Zucchini

Phytophthora develops rapidly during warm, wet weather. Poor drainage, soil compaction or excessive overhead irrigation will often trigger a phytophthora infection. It is a soil borne disease. Fields with short rotations are at high risk of developing phytophthora. Other host crops include the solanaceous crops (peppers, eggplant, tomatoes and potatoes.)

Once present in the field, control of this disease is very difficult. The spores can live in the soil for more than 10 years. Spores can also move in water and may be carried by surface drainage and ground water movement. In Michigan, phytophthora spores have been found in irrigation ponds and streams.

Phytophthora has been identified in a number of fields in the Harrow area this year. In past years, it has also been seen in reas of Norfolk and Elgin counties. The most effective way to manage this disease is through early identification and crop rotation. Rotate fields for a minimum of 3-years away from all host crops. If you suspect phytopthora in a vine crop field, contact OMAFRA or your local agri-business.