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Plant Sleuths Track Down A Tomato Virus

Posted on: Friday, 29 August 2003, 06:00 CDT

HAVING GARDENED for more than 25 years in Port Orchard and having diagnosed plant problems for much of my career, I know many of the common diseases that attack fruits and vegetables here. Sometimes though, I'm stumped.

For the third summer in a row, a mystery disease has shown up in my tomato patch. Typically, it affects the variety Early Girl, and has hit only one or two bushes out of the 30 or more plants I grow. Leaves all over the plant turn yellow, and their veins turn an unsubtle shade of violet. It's as if a demented Easter egg dyer has decided to try his art on a plant. Fruits on the infected plants are small but undamaged, and production is scanty.

I have a recent edition of the PNW Plant Disease Handbook, a joint publication of the Washington, Oregon and Idaho extension services. It describes causal organisms, symptoms and controls for about any disease that could befall a plant in the three-state region. Even with the help of this thoroughgoing reference, I had trouble diagnosing the problem. None of the diseases I read about seemed an exact match of what I was seeing on my plants.

Was the disease a rare one that somehow found its way to my garden? Or was it a common one showing atypical symptoms? Were several diseases attacking the plant at once, making for a confusing array of symptoms? Why was only one plant among many infected? Finally, I made a tentative diagnosis - aster yellows - a phytoplasm- caused disease that occurs rarely on tomatoes. The handbook indicated one of its symptoms is purple leaf veins.

Uncertain of my diagnosis though, I decided to send the entire plant to WSU-Puyallup, where a plant pathologist could examine it. My friends at the Kitsap Extension office had me complete a form that provided information to the pathologist about the sample. The process is similar to providing a short medical history to a doctor. Then they packaged that big plant, roots and all, and mailed it to WSU-Puyallup.

A few days later I received a report from the pathologist. Her diagnosis was a virus disease, probably curly top, which is spread by the beet leafhopper. Like aster yellows, curly top is uncommon in Western Washington; so is the beet leafhopper. But symptoms on my plant most closely matched that disease.

Because the Puyallup clinic isn't equipped to test plant tissue for the presence of viruses, the pathologist offered to send the specimen to a lab in Prosser for further testing. Before I could get back to her, she sent the sample. I think she was as curious as I to get the disease identified. Today I got the results - curly top virus. Both the pathologist and I are wondering what the disease is doing here. It's something of an anomaly.

There isn't any control for curly top. Shading the plants may discourage leafhopper feeding. Where only one or a few plants are involved, pulling them up and destroying them makes most sense.

I took you through this process with me to spotlight a resource we all have available to us - the diagnostic services of WSU Cooperative Extension. When you have plant problems you can't solve, there's free, competent assistance for you at Extension.

Trained Master Gardeners are the first-level of assistance. Frequently, they can identify your plant problems and discuss controls without sending samples to a lab. In King County, you can reach Master Gardeners at 206-296-3440 or 800-325-6165.

If they can't identify a problem, Master Gardeners have been trained to seek help from the next levels of assistance. Sometimes the help comes from an Extension agent trained in horticulture. Sometimes it comes from specialists such as the pathologist at WSU- Puyallup. Rarely, as in the case of my sample, special labs and experts at other branch campuses or at the main campus in Pullman provide the help.

I have experience with and trust in Extension's diagnostic services. Typically people at all levels of the system provide honest, competent and thorough information and assistance. How my tomato sample was handled is a case in point.

Chris Smith, who lives in Port Orchard, is a Master Gardener and is retired from the WSU Cooperative Extension. His columns appear in the P-I garden pages on Thursday. Send questions to P.O. Box 4426, South Colby, WA 98384-0426.

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