Tomato spotted wilt virus is again showing up in West Side San Joaquin Valley tomato fields, though experts say pressures are not yet approaching the devastating level some growers have seen in recent years.

“This year, tomato spotted wilt virus is widespread and locally severe — up to about 12 percent to 15 percent incidence in a few fields I’ve looked at,” says Tom Turini, UCCE vegetable crops farm advisor in Fresno County.

W outbreaks are problematic in infected fields, he says, there appear to be fewer infested fields than the period from 2004 to 2007, which was marked by sometimes devastating losses. Damage so far this year is less severe where the thrips-vectored virus is showing up. Most of the infested fields are along the West Side corridor from Firebaugh to Huron.

Turini says a concerted effort among processing tomato growers to request transplants treated with neonicitinoids or to treat transplanted fields with drip-applied systemic insecticides seems to be helping contain the spread of the virus by keeping thrips in check.

Two seasons of data show no evidence that tomato spotted wilt virus is entering tomato fields on transplants, he notes. Rather, it’s most likely that overwintering thrips are moving into the field from outlying host plants.

“Controlling thrips is not easy, because there are no materials available that will substantially reduce populations for long periods of time. But because of the biology of the virus and insect, if we are able to bring populations down on a suitable host, we can make a regional impact,” Turini says.

With funding from the California Tomato Research Institute, he is working with tomato growers and PCAs to develop an effective control program that includes integrated insecticide applications in the field and greenhouse.