Southwest Michigan vegetable update – August 8, 2018
Birds and bacteria – What’s a grower to do?
Cucurbit downy mildew pressure will remain high for the rest of the season, especially when we get cloudy, cool, windy conditions. A tighter spray schedule with more effective products is advised by Michigan State University Extension. Morning dew conditions will continue to be conducive for powdery mildew spread. Heavy powdery mildew infections will lead to early defoliation, limiting fruit size and quality. Fruit without leaf cover are prone to sunburn which will break down in storage. Unprotected handles will also be affected leaving the pumpkin without a handle. All stages of squash bugs can be easily found.
Watermelon harvest has begun.
Crows and other birds continue to be a significant problem for many vegetable producers, especially sweet corn growers. Crows, however, are general feeders and attack many species including tomatoes (Figure 1), peppers, cantaloupe and they especially like watermelon. For vine crops, one of the best defenses is to maintain a good leaf cover over the fruit so fruit can’t be seen. Various audio and visual devices have some measure of control, but birds will eventually get used to them. The best deterrent I have found for crows is to shoot one and hang it up in the area you wish to protect. One dead crow is good for about a 200-foot radius.
Incidence of bacterial diseases in tomatoes and peppers has increased. Early infections of bacterial spot and speck start as small, gray to black spots on the leaves (Figure 2). As infection spreads, the number of spots increase and coalesce. Eventually the leaf will turn yellow and fall off, limiting fruit size and exposing them to sunburn. Infection generally begins from infected seed and then spreads with rain splash and wind. The best control measure is to apply control products in the greenhouse on seedling transplants to limit the number of infected plants planted to the field. Proper field rotation will also help. Once in the field, the various copper products have limited effect on bacterial spot and speck since the diseases have developed tolerance.
Figure 2. Bacterial infection on tomato. Early infection (left) showing small dark spots. Advanced infection (right).