Issue: March 8, 2003

Curly top virus and heirloom tomatoes

What is curly top virus and is there a cure for it? I have received about 15 different varieties of Heirloom Tomatoes, and I do not want to expose them to this virus.Larry S. Las Vegas, NM

Curly top virus is a plant disease that affects many garden crops, especially tomatoes and chile. While this virus is harmful to plants, it does not harm people, so the concern is exclusively for our plants. The virus cannot overwinter in the soil; it must remain in a living plant. Plants cannot be infected by planting them in soil where infected plants grew last year or by use of compost from infected plants. Infection involves transfer of the virus from plant to plant by insects. Some perennial weeds, some landscape ornamentals, and especially the London rocket (mustard weed) carry the virus through the winter. The most common method of disease transmission is by an insect called the beet leafhopper. As the insect feeds on the weeds, it takes in some of the virus. When the insect feeds on a tomato or chile (after picking up the virus), it may then transmit it to the vegetable. Symptoms of curly top include yellowing of the new growth, curling or twisting of the leaves, and often development of a purplish cast on the mid-rib on the underside of the tomato leaf. Perhaps the least desirable symptom is that crop yield is greatly reduced. There is no cure, only prevention. Good weed management during the spring is essential. Removal of weeds that carry the disease should be accomplished before the susceptible vegetables are planted. Insect control is not effective. Treatment with insecticides will usually not stop spread of the disease. Row cover fabric surrounding tomatoes and chiles will provide protection from the spread of curly top virus. This may be a reasonable solution for limited numbers of plants. The row cover material will also provide some wind and sunscreen protection.

Bing cherry - few fruit

I have a miniature Bing cherry tree. I planted it 3-4 years ago. When it blooms, it has plenty of flowers but just after the cherries start to form, they dry off leaving no more than 10-13 cherries to pick. What could be the problem? Monica G.

The sweet cherry tree requires pollination to set fruit. In the last several years, there has been a shortage of honeybees. There have been a couple of mite pests that have killed many feral (wild) honeybee hives. If there are not enough bees active in the area, the cherries will not be pollinated. Weather can also prevent pollination. If the weather turns cool when the cherries are pollinating, bees will be less active, even if they have survived the mites. Finally, there should be another variety of sweet cherry nearby from which bees may bring pollen. A sweet cherry variety does not successfully pollinate itself. It must receive pollen from the nearby different variety of sweet cherry. Any of these may explain your problem. First, look to see if bees are active in the tree when it blooms. If so, notice the weather. And finally, look around to see if there are other pollinator varieties nearby. If not, you may need to plant a different variety of sweet cherry in your own yard.

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.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!