Vegetable Diseases

With warmer weather and good growing conditions finally here, the summer vegetable crops should begin to take off. We also should begin to see many of the leaf spotting fungal and bacteria in the garden.

Each year, every gardener likely encounters Septoria leaf spot on tomatoes, anthracnose of cucumbers and beans and other fungal leaf spotting and bacterial leaf spot diseases of vegetables. In addition to the many fungicides that could be used, there are several non-chemical management tactics that will help reduce incidence of fungal and bacteria leaf spots. Because almost all

Septoria Leaf Spot

fungi require moisture to grow and bacteria are spread by water, altering air circulation around plants to promote leaf drying and attention to irrigation techniques will help create a less favorable environment for fungal growth. Prune or space plants so that they are not overly crowded. Open plant canopies by pruning or weeding to help promote leaf drying after heavy dews or irrigation. Use drip irrigation instead of overhead watering to reduce the amount of time leaves remain wet. The longer period of leaf wetness, the greater the opportunities for fungal infection.

Because many of the leaf spotting fungi overwinter in the soil on crop debris and are transferred to the new crop of plants through splashing rain water, mulching plants with straw, composted grass clippings or other material will reduce the amount of inoculum coming in contact with the plants. At the end of the growing season, remove crop debris or till it under.

Cucumber leaf with lesions caused by the anthracnose fungus

A number of fungicides are available for use in gardens. A survey of the lawn and garden centers in the Columbia area revealed that they are found under a variety of brand names, with the active ingredients chlorothalonil, copper, maneb and sulfur. If you are trying to control a bacterial leaf spotting problem, a copper-containing compound is the best choice. Many of these products also contained an insecticide and some even a fertilizer. As a rule of thumb, avoid using these combination products unless you need all of them. Using an insecticide when not needed may kill some of the beneficial insects that keep the pest insects at tolerable levels.

Laura Kabrick, Extension Assistant, Plant Diagnostic Clinic, UMC (573)882-3019