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Archive for Sunday, July 11, 2004

Fungal diseases thrive in rain, warm weather

July 11, 2004

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It's strange to hear gardeners in July muttering "I wish it would stop raining," considering the drought of the past three years.

Rain and warm weather have led to the development of two deadly fungal diseases in the vegetable garden. Septoria leaf spot and early blight are starting to show up in tomato patches in Douglas County.

Septoria leaf spot causes small, brown to black lesions, while early blight results in larger, target-shaped spots. Infected foliage turns bright yellow, then brown and eventually drops from the plant. They 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 necessary.

Here are other tips to counter leaf spots and blight:

  • Stake or cage plants to increase air movement and reduce conditions favorable for fungal infection.
  • Use straw mulch around the plants' base to help prevent splashing water from spreading the disease.
  • 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.
  • Control weeds in the garden. Not only do they compete for moisture and nutrients, they crowd the tomatoes increasing humidity and blocking air flow.
  • Use fungicides.

Applications every 7 to 21 days will help slow or stop the progression of fungal diseases. Begin applications as soon as the first leaf spots are noticed. Do not wait until you see heavy leaf spotting because it is difficult to stop the disease 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 the fungicide off, you will need to reapply. As always, read and follow the label directions.

Tomatoes are the No. 1 vegetable grown in home gardens. Unfortunately, they can also be the No. 1 plant for problems. Check daily for diseases and insects; use good management practices and spray chemicals only when needed. Then use the bumper crop to make your favorite homemade salsa again this year.

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