Blossom end rot is a disease of tomato and peppers that is not actually an infectious disease. Photo from the University of Maryland Extension.

By John E. Woodmansee
Agriculture/Natural Resources Extension Educator, Purdue Extension Whitley County

COLUMBIA CITY — After discussing weeds and insect pests, we conclude our “unwanted garden guests” series today on the subject of diseases. Many gardeners struggle with diseases because often the disease is not noticed until it’s in advanced stages, and then it’s too late to save the plant.

Let’s start with the disease of tomato and peppers that is not actually an infectious disease: blossom end rot. If you have grown tomatoes or peppers, you’ve probably seen this one — a black leathery spot on the base of the fruit.

John Woodmansee

Rosie Lerner, a retired Purdue consumer horticulture specialist, wrote about this disorder. “Blossom end rot is thankfully not an infectious disease, but rather a frustrating disorder of the fruit,” she said. “The black scar tissue is thought to be caused by a deficiency of calcium in the developing fruit.”

In most cases, blossom end rot is brought on by extreme fluctuations in soil moisture. To reduce these fluctuations, watering during dry spells and mulching to conserve soil moisture will help encourage steady growth and calcium supply in the fruits.

“Some folks recommend spraying the plants with calcium, but by the time you see the scar on the fruit, it is too late,” she said. “Most Indiana soils have plenty of calcium, although some sandy soils may be deficient.”

Another common disease of tomato is the fungal disease, septoria leaf spot. The disease causes dying spots on the leaves after the first fruits set, which eventually coalesce into large necrotic (dead) areas. It typically progresses from the lower leaves upward on the plant. Although fruit yield and quality suffer, this disease gives the appearance of healthy fruit on a dying plant. Gardeners can remove affected leaves, practice crop rotation, and practice sanitation by removing and destroying tomato plants in the fall. Additionally, fungicides can be used to prevent new infections.

Sweet corn is rarely grown in small homeowner gardens, but for those who have more space, it’s a popular vegetable. One disease of sweet corn that looks somewhat alien is common smut.

According to Purdue Extension publication ID-405, “Sweet Corn Pest Identification and Management,” this disease produces gray to white enlarged galls on ears, leaf surfaces, stalks, or tassels. Ear galls are often associated with poor pollination conditions. Fungal spores overwinter in the soil and are spread to plant surfaces by wind and splashing rain.

Insects, hail, or mechanical injuries increase disease incidence. Infection is not systemic, so galls on one plant part do not mean galls on other plant parts. Dean Malvick, Extension pathologist for the University of Minnesota, suggests managing this disease by choosing resistant hybrids, crop rotation, and maintaining proper soil fertility.

If you would like to compare a vegetable disease you are noticing with some representative photos, go to ag.purdue.edu/department/arge/swpap/veg-disease-photos.html.

For more information about vegetable diseases and other aspects of vegetable production, visit Purdue’s Vegetable Crops page.