Bob Hammon, CSU Extension, Tri River Area

Curly top is one of several insect-vectored viral diseases that affect tomatoes. Seventy-five percent losses can occur in Western Colorado when conditions are favorable for the spread of the beet leafhopper (Circulifer tenellus), the vector of the virus.

Ideal conditions occur when fall and winter rains in the desert areas of New Mexico, Arizona, and Sonora and Chihuahua Mexico allow winter annual mustards to flourish during the winter months. Beet leafhoppers feed and multiply on these plants, then migrate north on storm fronts and with prevailing winds when the host plants mature in the springtime.

The severity of the curly top infestation in western Colorado is dependent on the timing of the beet leafhopper arrival and their numbers. 2003, 2004 and 2005 had severe curly top infestations, with 75% or more losses in susceptible tomato varieties. Roma tomatoes were a complete loss for many growers.

Beet leafhoppers are just one of many leafhopper species that are present in western Colorado during the summer months. They can be difficult to identify without using a microscope. Growers can get a rough idea of their arrival time and abundance by watching for leafhoppers on kochia plants during May and June. For information on biology and identification of the Beet Leafhopper check out the High Plain IPM website.

Curly top virus symptoms begin to appear on tomato plants a week or more after they are infected by leafhopper feeding. The first symptoms are leaf rolling and a color change. Be careful about using leaf rolling as a symptom to diagnose the virus because there are many different causes of leaf rolling in tomatoes. As the disease progresses, the leaves yellow and veins turn purple. Infected plants eventually turn yellow and die. Note the size and color differences in the following two photos.

Symptoms of Tomato Curly Top Virus
Symptoms of Tomato Curly Top Virus
Click thumbnails for a larger view of the photo
Symptoms on other vegetable crops: Beans, Beets, Bell Pepper, Pumpkin various Squash, and more tomatoes.

Curly Top Virus can be confused with Tomato Spotted Wilt Virus

Symptoms of tomato spotted wilt, caused by a virus spread by thrips, can be confused with curly top symptoms. The upper young leaves of tomato plants infected by tomato spotted wilt virus (TSWV) bronze and develop small dark spots or flecks. Curly top infected plants do not exhibit spots or flecks on the foliage. TSWV is responsible for the distinctive concentric rings seen on green and red fruit. The same conditions responsible for the movement of beet leafhoppers into tomato fields are also responsible for the increase in TSWV problems. Read more about TSWV (link or pdf).

Curly Top Research in Western Colorado

TRA Extension conducted research in tomatoes during 2006-2008 to evaluate methods of controlling curly top virus. In 2006, we conducted demonstration trials to evaluate tomato varieties for resistance to the virus. We also evaluated walls-of-water and floating row covers as control tactics. 2007 research research looked at planting dates and row covers as management techniques in trials conducted at the Western Colorado Research Center at Orchard Mesa. Replicated trials were conducted in 2008 to look at the impact of plastic mulch color on curly top incidence. A planting time insecticide and SAR (Synthetic Acquired Resistance) trial was conducted to evaluate control options for commercial growers.

Click the following to view results of those trials.

2008 2009

This page was updated on March 3, 2016