From the ground up: Ward off tomato blight, other disease by watering ground

Tomatoes have a lot of enemies in the garden, even deer. But more common are the fungus and bacterial diseases of tomato plants.

Tomato blight and leaf spot is common and attacks foliage, particularly the lower leaves. Early blight, Septoria blight and Late Blight all have the overall effect of leaves turning yellow, brown, then withering and dying.

These are all caused by a fungus that overwinters on plant debris in the soil. Fungal spores splash onto the plant’s leaves by raindrops or watering.

Wet spring and wet early summer weather favors development of foliar diseases on tomatoes.

There also are bacterial spot diseases that behave the same way as the fungal diseases, which can affect foliage and fruit.

Bacterial spot, bacterial speck and bacterial canker are some common ones.

Then there are wilt diseases, most common are Fusarium and Verticillium wilt. Plants infected by Fusarium wilt show leaf yellowing and wilting initially on one side of a leaf, branch or plant, spreading to the remainder of the plant. Verticillium wilt causes yellow blotches on lower leaves; the leaves rapidly turn completely yellow, wither and drop off. Both wilts affect the water-conducting tissue in the stems.

Blossom-end rot and fruit cracking are the two most common issues attacking the fruit of the tomato plant.

Both are caused by a calcium deficiency that is related to wide fluctuations in watering. Iowa soils contain plenty of calcium, so the addition of calcium doesn’t solve the problem, but a consistent supply of moisture does.

Good cultural practices in the garden help avoid some of these issues. Iowa State Extension recommends rotating tomatoes in the garden every year, and not planting them in the same spot for three years.

This helps to destroy the pathogens that live in the soil. That’s hard to do in a small home garden.

Other tomato tips include:

• Space plants at least 3 feet apart, allowing good air circulation for faster drying of foliage.

• Staking tomatoes. Don’t let them sprawl along the ground.

• Mulch tomatoes with at least a 2 to 3 inch layer of mulch that helps prevent the soil from splashing onto the plant.

• Avoid getting plant foliage wet when watering. Apply water directly to the ground around plants with a soaker hose, slow running hose or watering can. Water only in the morning so the foliage doesn’t stay wet all night.

• Don’t work with plants when foliage is wet.

• Remove diseased leaves to reduce the spread of the spores and remove all plant debris in the fall.

• Plant disease free and disease resistant varieties of tomatoes.

For all your tomato questions, call the Linn County Extension Hortline at (319) 447-0647.

• Lisa Slattery is a Linn County Master Gardener.

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