Tomato powdery mildew is usually restricted to the southwestern US, but has been problematic in Minnesota in recent years.  |
Symptoms: Symptoms appear as small yellow to green spots on the upper sides of leaves. A white powdery covering may also develop on the under sides of leaves. Lesions may turn brown and entire leaves may die, but seldom drop from the plant. Photo by Plant Disease Clinic |
| Causal organism: | Oidiopsis sicula, Erysiphe orontii, Odium lycopersicum |
| Over wintering: | In infected plant material, debris, and some weed hosts (in warmer climates). In Minnesota, the causal organism is most likely introduced from translplants grown in warmer climates. |
| Months of infection: | June-September |
| Method of dispersal: | Wind-borne spores |
| Infection point: | Penetration of leaf tissue through natural openings (stomata) |
| Control: | Plant only disese-free plants and inspect plants weekly. Increase spacing between plants to improve air circulation, and water in the mornings at base of plant to reduce humidity. If symptoms develop, remove infested leaves and destroy. |
| Labeled fungicides | Sulfur fungicides, though usually not required. As always, follow manufacturers' instruction. Note: Do not apply sulfur at temperatures above 95 since burning may occur. |
| Comments: | High humidity favors development of disease, mild temperatures favors infection, and high temperatures favor death of infected leaves. |
| For Additional Information | Back to Tomato Diseases |
