While tomato spotted wilt virus infections are moderate, Turini reports that curly top virus has caused substantial economic loss in tomato fields this season.

Damage is most prevalent in fields along foothills, which until this year had been treated under a California Department of Food and Agriculture (CDFA) area-wide management program to reduce migrations of beet leafhopper populations that transmit the virus. The CDFA Curly Top Virus Control Program this year did not treat foothills; as a result, it appears populations are building.

“Curly top occurs occasionally, and this is one of those years that it is worse than most,” Turini says. “It’s only one season, but evidence is pretty compelling that not treating the foothills has been a factor.”

The effect of curly top on processing tomato crops varies, depending on when plants are infected in their development. Early infections halt plant growth, and fruit that does set will be stunted and color prematurely. In later stages of development, curly top can cause plant death, yield losses, and fruit size reduction. CTV-infected plants can often be distinguished by upright growth habit, curled leaves, and chlorotic leaves with purple veining.

Because leafhoppers tend to feed sporadically on tomato plants within a field, plants can sometimes compensate and limit yield losses. In other fields, depending on the distribution of the virus, yield losses can be severe. Losses are typically most severe on the edge of the field where leafhoppers migrate.

Turini says growers should scout carefully for beet leafhopper and consider treatments to stop the regional spread of the insect and limit the transmission of the virus.