Use appropriate measures to control weeds and volunteer potatoes and tomatoes in production areas. Maintain fertility at optimal levels-nitrogen and phosphorus deficiency can increase susceptibility to early blight. Time applications of overhead irrigation to allow plants to dry before nightfall. Although the above measures are important to minimize infection, it is usually necessary to apply fungicide sprays to fully protect plants from early blight. Applications to tomato are usually begun 2-3 weeks following emergence or soon after transplanting if a calendar schedule is followed.
Late blight is a fungus causing diseases which affects potatoes and tomatoes.
It most often occurs in long wet periods of weather. The disease first manifests itself as dark green or black water-soaked spots. Occasionally the affected leaves will have a white powdery mildew on the underside of the leaves. Leaves will droop and appear as though they have been scalded or frost bitten. Fruit will develop rot and decay.