General situation We are firmly into the 2020 season and the weather is starting to settle into its summer pattern. According to the data from our reference weather station the Merced area is running slightly ahead of the 30 year average. A high in the mid 90's is forecast for Thursday with temperatures building to that peak and then declining again slowly. That sort of temperature pattern will certainly accelerate thrips development so we might see some changes in predicted dates for generations as we pass through the next 2-3 weeks.
Thrips generation timings According to the degree-day projection, we are just past the peak for generation 2 (May 6th) Unless you are seeing early TSWV symptoms, or consider crops to be at high risk, it's unlikely that generation 2 will be carrying much virus, but if you are concerned about early attack please contact a UCCE adviser to discuss your situation. Generation 3 adults are predicted to peak on 6/3 (although, with hot weather on the way this might come forward a few days), with generation 4 following in the last week of June. Those two generations are the ones we would typically expect to be carrying the first significant levels of TSWV. The current projection runs until July 1. We'll be extending the projections this week and posting another update in 7-10 days.
Special Note: SW-5 resistance breaking strains of TSWV have been detected at multiple sites in Fresno Co in the last week or so. Although we haven't yet seen issues with resistance-breaking strains as far north as Merced, be aware that these strains of the virus are out there and likely to spread over time. If you see suspicious symptoms in SW-5 varieties please let your local UCCE adviser know. We can arrange for samples to be collected for testing.