General situation: Things have warmed up recently. Our reference weather station for Fresno is running about 3 days ahead of last year and a week ahead of the 30-year average for heat accumulation, so far this season. We're into day 2 of a 4 day mini heat wave and that is sure to speed up thrips development. Friday is forecast to see the intense heat break a bit, but there might be gusty winds, so may not be suitable for some field operations. Things are set to cool off again for most of next week, but temperatures will still be right in the sweet spot for thrips development, so we can assume that we're into the period of continuous vector activity from now on. For those who check the website, we updated the projection graphs out to the end of August today, to give you a look at how the season is projected to play out at this point.
The current projections for generation peak times are as follows: Generation 3 adults will peak on May 27th, Generation 4 will peak on June 19th, and Generation 5 on July 9th. Generations 3 and 4 represent the major risk of TSWV getting into crops before fruit set, so if you're planning to use insecticides to knock down thrips numbers, the next month or so is an important period.
TSWV: Remember that Fresno Co. is the hotspot for development of resistance breaking TSWV. We have already seen TSWV in some fields in the county and tests done at UC Davis have confirmed that the virus is a resistance-breaking strain. Given the weather conditions and the confirmation of resistance-breaking TSWV already this season, we are anticipating that at least some locations will see heavier damage this season than in previous years. Now is the ideal time to suppress thrips populations by using a suitable insecticide. Protection of crops at this time of year delays the infection until the most susceptible crop growth stage (pre fruit set) is past. If you see TSWV symptoms, especially if the variety carries the SW5 resistance gene, please let your local UCCE adviser know and arrangements can be made for samples to be collected and tested for TSWV and resistance-breaking at UC Davis.