Tomatoes are the number one vegetable grown in home gardens. Unfortunately, they can also be the number one plant for problems. The relatively dry summer weather has not been favorable for development of leaf diseases on tomatoes.
Nevertheless, with the recent rain and high humidity, problems may start to show up in the next couple of weeks. Taking preventive steps now may help you win the disease battle and reap a bountiful harvest.
The two most common fungal leaf spots are Septoria leaf spot and early blight. Septoria leaf spot causes small, brown to black lesions. Early blight results in larger, target-shaped spots. Infected foliage turns bright yellow, then brown and eventually drops from the plant. Both maladies initially attack the lower, inner foliage then progress up the plant, killing more and more leaves. The plant may not die completely, but tomato production is greatly reduced.
Leaf spots can be suppressed by a combination of cultural and chemical methods.
Because both diseases overwinter on dead plant debris, a complete cleaning of the garden area is a must.
Next, stake or cage plants to increase air movement and reduce conditions favorable for fungal infection.
Third, use straw mulch around the base of the plants to help prevent splashing water from spreading the disease.
Fourth, when watering, only wet the soil around the plant and try to keep the leaves dry. Wetting the leaves late in the day, coupled with dew formation at night, increases the number of hours the leaves remain wet and increases the chance of getting fungal infections.
Fifth, control weeds in the garden. Not only do they compete for moisture and nutrients, they crowd the tomatoes increasing humidity and blocking air flow.
Finally, use fungicides. Applications every seven to 21 days will help slow or even stop the progression of these fungal diseases. Begin applications as soon as the first leaf spots are noticed. Don't wait until you see heavy leaf spotting because it is difficult to stop them at that point.
Products that have Chlorothalonil as the active ingredient, such as Fertilome liquid fungicide and Ortho liquid fungicide, work well. Other products to consider are Daconil, mancozeb and copper-based products like Bordeaux.
If rainfall washes off the fungicide, you will need to reapply. As always, read and follow all the label directions.
Check for diseases and insects daily, use good management practices, and spray chemicals only when needed. Then use the bumper crop to make your favorite homemade salsa again this year!
The Garden Calendar is sponsored by K-State Research and Extension-Douglas County office and written this week by Bruce Chladny, county extension agent, horticulture. For more information, call the Master Gardener Hotline, 843-7058, from 9 a.m. to noon and 1 p.m. to 4 p.m. Monday, Wednesday, or Friday.