Ok ok very sorry! Powdery Mildew on Vegetable Crops GardenLine | Vegetables | Powdery Mildew on Vegetable Crops Sharon Faye Powdery mildew has many species and which attacks a wide variety of vegetables. Species affected by powdery mildew include plants such as: dill, parsley, parsnips, peas, beans, carrots, turnips, cabbage, broccoli, cauliflower, radishes, beets, etc. The fungus is usually carried on the seed or spread by wind. It develops on the leaves or other plant parts into a white powdery talcum-like mold. Reproductive spores form on the white mold and in perithecia (tiny, dark coloured reproductive structures) and then are spread. Humidity allows spores to germinate, while rainfall may wash spores off the plant causing them to burst rather than germinate. Even on the leaf, spores do not germinate well in water droplets. POWDERY MILDEW OF: Peas: Leaves, stems and pods may be affected by the powdery mold. It may be first noticed as discoloured spots on the upper surface of leaves, which eventually turn powdery and enlarges covering the entire leaf. The plant tissue below may turn purple, then brown. Later in the season, vines may dwarf, mildewed areas wither and eventually the whole plant may die. Crucifers (Turnips, Broccoli, Cauliflower, Radishes): Spots of the mold first appear on the upper surface of leaves and stems until it covers them completely. Later the leaves may become pale green to yellow or tan. Mildew on the cauliflower’s inner leaves around the head encourages the entrance of soft-rot bacteria. Crucifers are not usually killed by the fungus. Usually plants are stunted and partially defoliated depending on the stage of growth when infected. Cucurbits (Cucumbers, melons, pumpkins, squash): Spots of white mold on the shaded underside of crown leaves, which may expand and coalesce (merge together). The leaves may become dry and brittle as they die exposing the vine to sun- burning. The secondary effects on fruit would be an increase in sunburning, premature ripening, poor flavour and texture. Carrots: Older leaves are covered first with a dirty white fungus. Younger and inner leaves are at first spotted with mats of mycelium of the fungus which enlarge and join to form larger areas. A slight chlorosis (yellowing) may occur but death rarely occurs even when plants are severely infected. Beets: Spores develop on either side of the leaf. The spots may increase in size covering the leaf, causing it to die before root size and sucrose (sugar) levels have reached their maximum limits. Beet mosaic yellows virus increases the susceptibility of beets to powdery mildew. Beans: The fungus is first noticed on the upper sides of the leaves. In severe cases, the stems, petioles and pods may be covered as well, while the plant tissue below becomes reddish-brown and finally the leaves may turn yellow and drop off. Control: There are some general practices which help to control powdery mildew, such as: – Crop rotation. – Use resistant varieties where available. – Good air circulation/low humidity. – Good soil drainage. – Use water sprays and maintain optimal soil moisture for the crop. – Eradicate crucifer weeds and volunteer plants. – Plough down debris from diseased plants or remove from garden area. – Use pathogen free seed. Peas may be treated by soaking for 30 min. in 50o C (122o F) water. – Foliar fungicides may be used. Be sure to read labels carefully for their use on specific crops. Sources: Pennsylvania State University, College of Agriculture; Identifying Diseases of Vegetables.
A.F. Sherf and A.A. Macnab; Vegetable Diseases and Their Control; 1986.