Leaf Spot (fungus – Alternaria sp.): Small to medium size spots develop on leaves. They are usually yellowish when young and later turn brown (See Photo). The disease is favored by warm, wet weather. Sustained leaf wetness favors infection. Cultural controls include a wide row spacing to permit air circulation so that leaves stay wet for a limited period of time.
Powdery Mildew (fungus – Erysiphe sp.): Leaves are covered with a fine, white powdery coating (See Photo). The disease is favored by warm, dry weather. Altering row spacing and row orientation into prevailing wind will allow air to circulate within the crop canopy, reducing the highly humid microclimate that favors disease development.