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Gardening: Tomato diseases can halt growth

The race for the ripe tomato is on! We seem to be getting a late dose of heat and that’s good for turning the green orbs into something red and luscious. That is if you have a short-season variety and we don’t get an early frost.

Along with the heat though, a couple of common problems have been showing up at the WSU Master Gardener Plant Clinic.

Beet curly top is a virus that can appear in tomatoes as well as beets, peppers, beans and spinach and members of the cucumber family. It is carried by the beet leafhopper (Circulifer tenellus) as it flies from plant to plant in a garden or field. Leaves of infested tomato plants become dwarfed, crinkled and roll inward, and cup upward. Veins on the underside of leaves usually turn a purple color and may be roughened. The leaves also often produce swellings or spinelike outgrowths. Roots are stunted and may show a proliferation of secondary rootlets. Phloem tissues become necrotic and appear as dark rings when viewed in cross section.

There is no cure for curly top. Insecticides could control the leafhopper but the bug is long gone by the time the virus takes hold. The plants will not recover or set more fruit. Large nearly ripe fruit may ripen but smaller, greener ones won’t. It doesn’t readily spread between plants or stay in the soil so infected plants can be composted as long as the compost heats up to around 150 to 160 degrees.

Curly top can be confused with physiological leaf roll that we have also seen this year. This is a cultural condition brought on by our cool, wet spring and results in tomato leaves rolling downward but remaining a healthy green color. The condition usually goes away as the weather warms.

Another problem we’ve seen a lot of is blossom end rot. Tomatoes affected with this disease will have a tan, soft, watery patch on the bottom of the fruit at any stage of development. The patch can cover a third to half the fruit and often dries out to a leathery skin.

Blossom end rot is a physiological disease brought on by rapid drops in soil moisture when the plants and fruits are growing rapidly. The changes in water supply affect the availability of calcium which is a factor in the disease. This year our cold June slowed the development of tomato roots so when the hot, dry weather arrived in early July, the plants could not keep up with the water demand.

The best way to prevent blossom end rot is to make sure tomatoes get a regular deep soaking. How often that needs to be will depend on your soil type. Sandy soils will need to be watered more frequently than heavier clay soils. In my garden with soil high in organic material I drip irrigate for 45 minutes every other day. That gets water a foot into the soil. Once the tomatoes start reddening up I will back off on the water to prevent them from splitting.

Pat Munts is a Master Gardener who has gardened the same acre in Spokane Valley for 30 years. She can be reached by email at