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Ag Matters Column: Prevent tomato disease with these simple tips

Garden fresh, juicy red tomatoes are one of the true joys of growing a garden. However, all too often, your toils end in disappointment because of diseases that either reduce the yield or devastate your crop.

Leaf disease in tomato is typically one of two organisms, Alternaria (Early blight) and Septoria Leaf Spot. Septoria Leaf Spot is most evident around fruit set while Alternaria may be present during all growth stages.

Since they are similar in appearance, it's often difficult to differentiate between them. Both cause leaf spots that form on the lowest, oldest leaves and progress upward. Infected leaves turn yellow, shrivel and die.

Septoria leaf spots are small, numerous, dark spots that frequently have white to grey centers. Alternaria leaf spots are larger, less numerous and exhibit a target pattern, caused by "rings" of dead tissue.

Both organisms reside in the soil, so if weather conditions are right -- and if you have susceptible varieties -- you will likely experience the problem again.

There are several cultural techniques that should be implemented before you consider chemical treatments.

Fungicides are dangerous pesticides with innocent sounding names and are often misused and over applied, so avoid using them until you have exhausted the following cultural options.

Begin with a proper crop rotation. Do not plant tomatoes where you had potatoes, peppers, or eggplant -- and of course tomato -- last year. Rotation is important and is your first defense in disease prevention.

Plant a variety of tomato that is resistant or tolerant to leaf blight, sometimes, disease can be prevents simply by variety selection.

Do not crowd the tomatoes, lack of air circulation favors disease development. Leaf diseases need longish periods of uninterrupted wetness on the leaves for disease development, and overcrowding prevents leaf drying.

Use a trellis system or cages spaced a minimum of 24 inches apart to keep leaves and fruit off the ground. This aids in the plant drying and keeps the soil-borne disease inoculum further away from the leaves.

Also, it keeps the fruit cleaner and reduces the incidence of spoiled fruit.

If you need to irrigate, water the ground, not the leaves. Sprinkler irrigation keeps the leaves wet, and splashes the disease inoculum from the soil onto the leaves. Soaker hoses or careful hand watering are a better alternative.

Plastic "mulch" laid on the soil surface prior to transplanting is a common practice in commercial production and works well in gardens too.

Commercially available plastic is available in 3 and 4-foot wide rolls in many colors. Clear and black may be the most readily available to the gardener, but red and green are often available at garden centers.

Clear mulch with some red will allow weed growth beneath the plastic, unlike the black and green colors. If you need to water the plants, water through the transplant hole.

Often, however, the plastic reduces water evaporation so watering is not necessary.

Pinch off the "suckers" growing at the leaf axis. Suckers produce unnecessary foliage and decreases air circulation around the plant.

Commercial growers will often leave one leaf beneath the first flower and remove all other leaf from that point and down.

Finally, don't apply too much fertilizer, especially nitrogen. Excess fertilization promotes succulent leaf growth which is often more prone to disease.

If you follow these recommendations, you will hopefully enjoy juicy red tomatoes with an added benefit -- fruit without pesticide residue.

If all else fails and you need to use a fungicide, remember that fungicides only prevent new infections, they will not cure existing leaf disease.

Fungicides should be applied according to the product label. Products labeled for tomatoes include: Mancozeb, Maneb tomato and vegetable fungicide, Chlorothalonil, sold under the trade names Daconil 2787, and Ortho Multi-Purpose Fungicide.

There are also organic, copper fungicides, which are most effective against bacterial diseases but control many fungal diseases as well. Bordeaux mixture and Liquid Copper fungicide are two such products.

For more information, contact me at the Polk County Extension office in McIntosh or at the Clearwater County Extension office on Wednesdays. Our toll free number is 800-450-2465. If e-mail is your thing, contact me at