Curly top virus and mustard weeds

I hear people saying that there will be a problem with a virus in our gardens this year because of the mustard. What does this mean? How can mustard cause problems in the garden?

Answer:

There are several winter annual weeds in the mustard family that are growing very well this year because of the moisture in most New Mexico soils. One of these, London Rocket, is known to allow the curly top virus to overwinter and then infect our garden crops in the spring (especially tomatoes and chiles). There are other plants known to allow overwintering of the virus, but the mustard weeds also provide food and harborage to insects (beet leafhoppers) that spread the disease to our garden crops. The mustard plants flower in the late winter and early spring and then die. When they die, beet leafhoppers that were feeding on them move to other plants for food, and in the process they carry the virus to other plants. The virus does little to harm the mustard, but it causes severe problems with tomatoes and chiles.

It is important to realize that this virus cannot survive in the soil. It must remain in a living host. London Rocket begins germinating in the fall when it is possible for insects to carry the disease from garden crops to the mustard. The mustard sustains the virus through the winter and allows its return to the garden crops. The curly top virus cannot remain alive in the soil, and unlike some bacterial and fungal diseases, it cannot reinfect plants grown in the same soils as plants that were infected last year. Curly top virus will not reinfect a garden through the use of compost made from plants infected with curly top last year. The mustard weeds are prospering now. In many parts of the state, they are flowering and preparing to form their seeds (to germinate this fall and cause problems next year). The best method to manage curly top virus is to manage the weeds, not to attempt to control the insects that later spread the disease. Removal of mustard weeds from the vicinity of your garden now (before the tomatoes and chiles are planted) helps minimize the problem. In some situations, it is not possible to remove all mustard weeds; however, by increasing the distance from the weeds to the garden, problems may be minimized.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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