- Author: Neil McRoberts
General situation With the wet spring crops and thrips alike are somewhat behind their usual schedule. Temperatures over the coming week to 10 days will climb into the 90's and might peak at 100F on Thursday. Combined with an absence of prolonged rain, this pattern should see thrips development accelerate. There is a possibility of scattered thunderstorms and rain showers over the next 10 days, but it's not clear at the moment if the low pressure area that would cause those will track across northern California.
Thrips generation timings We have extended the projection interval out to the end of June. The current projection shows generation 2 egg hatch peaked around mid April and generation 2 are peaking now. We are currently projecting generation 3 adults will peak in the last week of May, with generation 4 adults possibly peaking around mid May. TSWV has been detected in the Fresno region this season, but incidence is still low so generation 2 adults probably do not represent a high risk of spread of the virus. However, resistance breaking strains of the virus are known in this area, which means that good thrips control is even more important than it has been in the past few years. Remember, controlling thrips numbers early in the season delays the spread of TSWV and gives crops a chance to get past the most susceptible stages, pre-flowering, before the virus incidence begins to increase. If you're planning to invest in thrips treatments this season, treatments will be most cost-effective if applied to control generation 3 or possibly generation 4. Treatments can be scheduled from now onward through the end of June.
Update on resistance-breaking TSWV So far, resistance breaking strains of TSWV have only been detected in Fresno Co, not in the upper San Joaquin Valley or Sacramento Valley. We know from surveys this year that the resistance breaking strains did over-winter, so there are likely to be some further outbreaks this year, most likely close to the areas where they occurred last year. Action to remove weeds that can harbor TSWV has been taken in the hotspot areas. We will be providing updates as the season progresses. If you want more information about the situation, contact your local UCCE adviser.