General situation: Things have warmed up recently. Our reference weather station for Merced is running about a week ahead of the last of year and a whole 12 days 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. Things are set to cool off again slightly toward the end of the 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 31st, Generation 4 will peak on June 24th, and Generation 5 on July 15th. 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: We haven't had any reports of TSWV in the central San Joaquin Valley yet this season, but with crops well established and 2 to 3 generations of thrips probably now active since the winter, it's possible that any TSWV that over-wintered in weeds will have had the opportunity to start to move into crops. Although we've never had a detection of resistance-breaking TSWV as far north as Merced Co., Resistance-breaking TSWV has already been found further south in the Valley this season. In the long-term, spread of resistance-breaking strains is a concern. 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.