Issue: August 2, 1999

Tomato curly-top virus

The leaves on my tomato plants are turning yellow, and the plants seem to be dying. This started on one plant but has now spread to the neighboring plants. What can I do to save the rest of my tomato plants?

There are several diseases killing tomato plants in New Mexico this year. Some diseases are viral and others are fungal. In both cases, you should remove diseased plants.

I spoke to Dr. Natalie Goldberg, NMSU Extension Plant Pathologist, who thinks you have described curly-top virus symptoms. She is getting reports of extensive curly-top problems from many parts of New Mexico. In this case, removal of infected plants is especially important. Curly-top virus is spread from plant to plant by small beet leafhopper insects. After they feed on an infected plant, they carry the virus to each subsequent plant on which they feed. Insect control is not effective in preventing the spread of the curly-top; removal of infected plants is more effective if the plants are removed before the leafhoppers can spread the disease.

Because curly-top is not soil-borne (spread through soil), it is possible to replant tomatoes this year or next year at the same site. For this reason, you may also compost the infected plants as long as there were no fungal diseases involved. The compost cannot spread the curly-top virus to the plants next year.

From your description, we diagnosed virus; however, Dr. Goldberg and I also discussed the possibility of fungal disease as well. In this case there would be spotting of the leaves, wilting, and other symptoms. The yellowing of the leaves would probably begin at the base of the plant and progress upward with black spots developing on the leaves. If these symptoms are present, you may have fungal disease in your tomatoes. Removal of the infected plants is still recommended, but some of the other information above changes.

If your plants have fungal disease, it is unwise to plant tomatoes, or related plants such as chile and eggplant, in the same site this year or for the next couple of years. Fungi can be soil-borne and spread from the soil to the plant. Composting plants infected with fungi can also be a way of spreading the disease. If your compost gets hot enough, or if you treat the diseased plants to high heat before composting, you may avoid problems, but be careful. If you wish to compost plants which may have fungal diseases, you may solarize the plants to kill the fungi. Do this by sealing the infected plants in a black garbage bag which is then placed in sunlight. Allow them to remain in the sun for several days. As the plants in the bag are heated, the fungi will be killed. Of course, the plants are dead, but they may now be composted. This is a good practice for any plant you think may be diseased when you aren't sure and don't know what disease is present. Rotating your crops to different locations in the garden each year is also a good practice to avoid the buildup of diseases in the soil.