Thursday, June 24, 2021


Gardening Corner: Tomato Spotted Wilt Virus (TSWV)

This virus can affect dozens of plants, but tomatoes, being so common, are the most usual victim reported.

The easiest symptom to recognize is the distinctive color pattern on ripe fruit. If you see this (probably with some leaf spots) there is a good chance this virus is the culprit.

In some cases, the virus attacks early or is more virulent and does a number on the foliage and new shoots. The leaf symptoms start on new shoots and at first may look bronze, eventually turning into dead spots. On tomatoes, we usually see these spots more toward the base of the individual leaflets, but this isn’t always the case. Sometimes the virus kills shoots entirely! By the time we usually get to see the plants the disease has progressed to the point where there is a mess of dead shoots, and half-dead leaves. But the mosaic looking tomatoes are the most recognized symptom.

This virus is spread by tiny, hard-to-kill insects called thrips. You’ll need a lens to see them. These small insects have frilled wings and rasping mouthparts that tend to tear up new buds and leaves, leading to malformed growth. While feeding, they infect the plants with the virus. Even if you kill the insects, once infected the plant is a goner.

So what do you do? First look for symptoms to confirm this is the problem. You can check to see if there are thrips present as well with a hand lens or microscope. If you are sure you have the virus, remove the infected plants and try my best to control the thrips population. UC IPM suggests insecticidal soap.

Keeping weeds under control and watching for pests diligently is your best plan. Using yellow or blue sticky traps in the plant canopy is a good technique to monitor insect population.

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