Issue: February 9, 2008
Can last year's seeds cause curly-top virus problems this year?
I had a severe problem with curly-top virus in my tomatoes last year. This disease was identified by my local County Agent. I am preparing to start my seedlings now and was wondering if plants grown from seed I saved last year will cause this year's plants to be infected with curly-top.
Santa Rosa, NM
Dr. Natalie Goldberg, NMSU Extension Plant Pathologist, assured me that curly-top virus is not seed borne. So, your saved seeds will not be a source of reinfection this year. However, Dr. Goldberg warned that since you had a problem last year, you can anticipate problems again. There are measures you can take to reduce the problem, and perhaps the weather this winter was also helpful in reducing the potential for curly-top next summer.
If the fall and winter were dry, the curly-top virus may not have over-wintered well. The winter annual weeds that allow the virus to survive may not have developed or survived this winter. These weeds also provide winter food and habitat for the insects that transmit the virus from one plant to another. Cold dry winters reduce both the weed and insect populations. The previous winter, followed by your problem, was cold, but wet. This helped provide the proper conditions for winter annual weeds and curly-top virus survival.
However, even if the winter is cold and dry, some weeds will survive and the virus may still exist in your environment. You can reduce the potential for problems by eliminating the winter annual weeds from your property. Do this now so that any insects surviving with them cannot survive until you plant your garden this spring.
Since it is not possible for you to control weeds on your neighbors' properties, you can also do things to protect your garden from imported insects carrying the curly-top virus. The first thing to consider is that insecticides are not effective. You can take measures to keep the insects from your plants. Do this by growing the tomatoes in large tomato cages (large enough to contain the mature plants). By wrapping the cage with insect netting or fine mesh row cover material, you can protect your plants from the insects and diseases they carry. Dr. Goldberg points out that tomato plants are susceptible to infection by curly-top virus throughout the growing season, so the tomatoes must be protected through the whole season. That is why the tomato cage must be large enough to contain the mature plant.
There are some additional benefits to using the wrapping material. The wrapping material will provide protection from drying winds and it will provide slight shading which will benefit the tomato plant. The disadvantage is that the material must be unwrapped from the tomato plant to allow harvest and then reapplied to allow no gaps for insect entry each time you harvest.
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: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!