- Author: Neil McRoberts
General situation With the cool, wet spring crops and thrips alike are somewhat behind their usual schedule. Temperatures over the coming week to 10 days will start to climb and we will see mid 90's F days around mid-week, with temperatures in the low to mid 80's F the rest of the time. 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 adults will peak around May 9th. We are currently projecting generation 3 adults will peak in the first week of June, with generation 4 adults possibly peaking right at the end of June. So far this season TSWV incidence is still low so generation 2 adults probably do not represent a high risk of spread of the virus. 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, but 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. We will be providing updates as the season progresses. If you want more information about the situation, contact your local UCCE adviser.