Extension Educator, Horticulture
Tomatoes continue to be the most popular vegetable grown in home gardens. As a testament to their popularity last week's article "What's Wrong with my Tomatoes?" in the CU News Gazette prompted all kinds of calls to our office.
Although the article contained great information, gardeners were obviously hungry for how to solve the problem. Generally their questions started with "I saw this article and it sounds like the same problem I have every year on my tomatoes". Their description follows with the first symptoms as a yellowing or browning of the lower leaves.
With further inspection gardeners may notice the leaves have spots. The lower leaves may continue to turn brown but not drop off. The brown leaves hang like wet socks on the stem as the disease moves up the plant.
Leaf spot diseases which can include septoria leaf spot and early blight are common tomato problems. Both fungi cause spots and can cause the leaves to quickly yellow starting at the bottom of the plant. Septoria causes small water-soaked spots which become circular to angular with dark margins and grayish white centers. Early blight causes small brown leaf spots with a target-like series of concentric rings in each lesion. Click here for pictures.
To prevent leaf spots improve air circulation around plants. You should be able to easily walk around mature plants. Good gardening techniques of mulching, watering, and staking or caging vines will help. Try to keep leaves dry by watering at the base of the plant and watering in the morning.
As with all diseases sanitation is important. Remove and destroy infected leaves as soon as the symptoms start. Make sure garden is cleaned of debris in fall. Weekly fungicide sprays of maneb, chlorothalonil or copper starting at the onset of disease can be helpful. If rain is predicted, spray fungicide the day before rain. Copper based fungicides are considered organic. Be sure to read and follow all label directions.
Leaf spot diseases can be easily controlled in the garden in the beginning stages of the disease, but are tough to manage once the plants are ravaged by the disease.
Selection of disease resistant varieties such as the early blight tolerant Mountain series developed at North Carolina State (Mountain Pride, Mountain Supreme, Mountain Gold, Mountain Fresh, and Mountain Belle) can help.
Unfortunately tomatoes can get several diseases. The fungal wilt diseases - fusarium and verticillium can also be a problem; however most hybrids show resistance. As in the leaf spot diseases, leaves of the plants infected with the fungal wilt diseases will turn yellow and die starting at the base of the plant and progress upwards. However wilt diseases will not show the dark spots on the leaves. With wilt diseases infected plants may also appear stunted. Leaves on only one side of the plant may show symptoms. Wilting might occur during the hottest part of the day even when plants appear to have adequate water. Both fusarium and verticillium cause discoloration of the inner stem tissue.
Both fusarium and verticillium are soil borne diseases and infect plants through the root system. They are not controlled by fungicides. Selecting resistant varieties and crop rotation are the best options for the wilt diseases. Look for VF or VFN on the label after the name.
Other factors can cause wilting of tomatoes including root rots, mechanical injury to roots or stems, toxins from walnut trees and a bacterium. The bottom line is to get an accurate identification of the problem before you reach for the fungicides or prune at ground level. Suspected plants can be taken to your local UI Extension office or the UI Plant Clinic at 1401 St Mary's Road in Urbana. 217-333-0519