Extension Educator, Horticulture
Dreams of deliciously delectable fresh garden tomatoes dance in our heads. No "store-bought" tomato can compare to a home grown one which ensures that tomatoes continue to be the most popular home grown vegetable.
Regardless of their popularity in the garden, tomatoes have their share of insect and disease problems. The most common problem I hear occurs early in the season as tomato leaves turn yellow then die from the bottom up. Two fungal diseases Septoria leaf spot (Septoria lycopersici) and Early Blight (Alternaria solani) can cause this symptom.
With these diseases the lower leaves start to turn yellow and then continue to turn brown and die. More leaves get infected as the disease continues upward until the plant has few healthy green leaves. The brown leaves often do not fall off and hang like wet socks on the stem. With close inspection gardeners may notice the yellow leaves also have spots.
Leaf spot diseases which can include septoria leaf spot and early blight are common tomato problems. 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. Early blight may also infect stems and the tomato fruits. Check this website for pictures. http://urbanext.illinois.edu/vegproblems/
Last year's dry weather actually kept down the incidence of these diseases, since as fungi both need water on the leaves in order to infect. The water can be due to rain, dew or over-head watering.
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. Make sure garden is cleaned of debris in fall and now before planting since both of these diseases over-winter in plant debris. This season remove and destroy infected leaves as soon as the symptoms start. 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.
We don't have much in the way of disease resistant varieties for tomato leaf spot diseases. There is the early blight tolerant Mountain series developed at North Carolina State which includes: Mountain Pride, Mountain Supreme, Mountain Gold, Mountain Fresh, and Mountain Belle.
Unfortunately tomatoes can get other diseases besides leaf spots including the fungal wilt diseases of fusarium and verticillium. Most hybrid tomatoes show good resistance to wilt diseases. Selecting resistant varieties and crop rotation are the best options for the wilt diseases. Look for VF or VFN on the label after the variety 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 S-417 Turner Hall, 1102 S. Goodwin Ave. in Urbana. Phone: 217-333-0519 http://plantclinic.cropsci.illinois.edu/
Join us at UI Extension offices in Danville, Onarga or Champaign for the UI Extension Telenet – "All about Tomatoes" on May 7 at 1 p.m. For more information http://web.extension.illinois.edu/cfiv/ or 217-333-7672.