Issue: March 24, 1997

Weed control to reduce curly-top virus


I remember reading somewhere that there are weeds which grow in the winter and cause curly-top virus in tomatoes. A couple of years ago most of my tomato plants died from this disease. Which weeds cause this problem and what can I do to control them?


London rocket, a winter annual mustard, is probably the main culprit. It first appears in the fall before freezing weather has killed the beet leafhopper which spreads the disease. Since this weed survives the winter, if it becomes infected with curly-top virus in the fall, it can sustain the virus until the spring. In mild winters it also sustains the leaf-hopper as well. Other weedy mustards which may contribute to the problem are tansy mustard and flixweed. These usually don't germinate until later in the winter, but can also harbor insects and the virus. Other weeds such as the perennial bindweed and silver-leaf nightshade may also be sources of virus infection, but probably not to the same extent as the mustard weeds.

This has been a pretty good winter for reducing the population of insects which can spread the virus, but there will still be some leafhoppers so eradication of the weeds is a good idea. The time to do this is now, before tomatoes and chiles are planted. In backyard gardens, a hoe will do an adequate job. In larger areas and agricultural fields, a broad-leaf herbicide may be the most efficient means of managing the weeds to prevent spread of disease. Use an herbicide labeled for control of the specific weeds you have present and read and follow all directions.

Moving daffodils


My daffodils are planted right where I plan to build a patio. They have finished flowering. When can I move them? They have bloomed beautifully for several years and I don't want to lose them.


You can move them now if it is absolutely necessary, but this is not the best time. If you can wait until the leaves turn yellow and die down naturally, the bulbs will be stronger and better able to bloom next year. If you must move them now, even if you leave the leaves on the bulbs, the leaves will die prematurely, before they can produce enough food to keep the bulbs at maximum strength. The bulbs will probably survive, but flowering may be less abundant next year.

What is calcareous soil?


What does it mean when they say our soil is calcareous?


The term calcareous refers to the abundance of calcium, or lime, in our soil. This is due to the fact that our dry environment has not resulted in the leaching of calcium and other salts from our soils. Some of these salts, such as sodium, can be toxic to plants at the level found in some New Mexico soils. Calcium, however, is not toxic, but it does alter the pH, or acidity, of the soil making it difficult for some plants to obtain the nutrients they need form the soil. Other plants, especially those native to calcareous soils, have no problem and flourish in our soils. The main message to remember is that we do not have to add lime to our soils. Acidification replaces liming in our part of the country.

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:, 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, or at the Desert Blooms Facebook.

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