We're seeing some early TSWV in areas of western Fresno Co. Here is up-to-date information from local UCCE adviser, Tom Turini:
In some specific areas within Fresno County, which include Five Points, Huron and Cantua Creek, treatment for thrips is suggested based on presence of the virus and the stage of thrips population development.
Within parts of western Fresno County (Five Points), Tomato spotted wilt virus (TSWV) was initially detected in tomatoes in early April. By 16 Apr, areas within a few processing tomato fields had as much as 5% of the plants showing symptoms. In the area north of Huron and west of Five Points, the virus was detected in lettuce earlier in the season. The TSWV strain in the tomatoes and in the lettuce can move within and cause disease of tomato plants with the TSWV-resistance gene (Sw5). Therefore, the pathogen that poses a risk to tomato production is present in this area.
Based on the Western flower thrips predictive population development model, peak egg hatch for generation two was on the 20 April and a substantial population of nymphs now exist. Peak for second generation adults is expected in early May. Thrips must feed on an infected plant as a wingless nymph to be capable of transmitting the virus as an adult. The winged, mobile adult can spread the virus within fields and to other fields. Therefore, an application of insecticides such as Radiant, Success or dimethoate to target the nymphs feeding on infected plants has the greatest potential of reducing spread of this virus.