Diagnosing Common Problems in the Vegetable Garden

What’s Wrong with My Tomatoes?

Tomatoes are one of the most popular vegetable crops grown by home gardeners, but they are sometimes plagued with diseases. To ensure healthy plants, provide tomatoes with adequate fertility by following soil test recommendations. Rotating crops in the nightshade/Solanaceae family (peppers, eggplant, Irish or white potatoes, and tomatoes) with other crops will help prevent serious problems. For help with tomato issues, contact the Garden Hotline at your Penn State Extension county office.

Early Blight

Affects: Foliage, stems, and fruit. Damage: Small, brown lesions, mostly on older foliage. Spots enlarge to form concentric rings, and the tissue around the spots may turn yellow. Cause: A fungus that survives on infected debris in the soil, seed, and volunteer tomato plants. Prevention: Do not plant tomatoes where other members of the nightshade family have been planted the previous year. Use mulch to prevent water from splashing from the ground onto the plants. Treatment: At the first sign of early blight, prune off all the leaves within 12 inches of the ground.

Septoria Leaf Spot

Affects: Foliage. Decline of foliage can lead to sunscald and poor flavor and color in fruit. Damage: Dark spots on leaves. Cause: A fungus most active when temperatures range from 68 to 77°F, the humidity is high, and rainfall or overhead irrigation wets the foliage. Prevention: Remove residue from previous related crops. Irrigate from below. Treatment: Prune off affected foliage.

Late Blight

Affects: Foliage, then the entire plant. Damage: Young leaf lesions are small and appear as watersoaked spots. These leaf spots enlarge quickly. Complete defoliation (browning and shriveling of leaves and stems) can occur within 14 days of first symptoms. Cause: A fungus carried by rain and wind. Infection increases when daytime temperatures are in the high 70°F range and humidity is high. Prevention: Grow resistant varieties. Plant in full sun and with adequate spacing to promote drying of leaves and fruit. A staggered planting may prevent all tomatoes from being affected when the fungal spores are present. Treatment: Pull out and destroy the entire plant to save nearby plants that are not yet infected. Fungicides must be applied before symptoms are visible.

Anthracnose

Affects: Fruit. Damage: Circular, depressed lesions. Infected areas change from tan to black and merge, resulting in large areas of decay. Cause: Wet conditions and delay in harvesting fruit. Prevention: Site plants in full sun. Allow for ample spacing between plants to increase air circulation and keep fruit and foliage as dry as possible. Stake plants to keep fruit from touching wet ground. Harvest fruit when ripe.

Home Vegetable Garden Top Three Most Unwanted Problems

Learn to diagnose and prevent some of the most common problems in the vegetable garden.

Powdery Mildew

Affects: Foliage of many vegetable plants, fruit, and ornamental plants. It is especially common on peas and cucurbits (squash, melons, and cucumbers). Damage: A white, powdery coating on the leaves and, sometimes, stems. Cause: Fungi that survive on plant debris and thrive in high humidity. The fungi are specific to the host plant. However, if one type of plant is affected, the conditions are also favorable for the development of powdery mildew on other species of plants. Prevention: Plant resistant varieties. Provide proper spacing to allow for good airflow. Remove affected plant debris from previous years. Treatment: Powdery mildew is mostly cosmetic. Cucurbit crops may benefit from an application of fungicide since they are most prone to leaf loss due to powdery mildew.

Cucumber Beetles and Wilt

Blossom End Rot

Affects: Fruit of peppers, tomatoes, eggplant, and, to a lesser degree, squash, and melons. Damage: Dark lesion or sunken area on the bottom, or blossom end, of the fruit. Cause: Calcium deficiency in the part of the fruit farthest from the stem. Wide fluctuations in available water are usually the cause since this affects the plant’s ability to absorb calcium from the soil. Prevention: Irrigate plants regularly and mulch to preserve soil moisture. Look for plant varieties that are resistant to blossom end rot.

This article was co-authored by Suann Leighow, Nancy Knauss, and Lois Miklas and first published by Penn State Extension on December 7th, 2021.