General situation It has been an up and down start to the year for thrips development. Through February the relatively dry winter, and somewhat warm start to the year in the San Joaquin Valley meant we were running ahead of the 30 year average for degree day accumulation. The last couple of rain events have slowed things down, but we are still ahead of the long-term average. Temperatures in the week ahead are predicted to be mostly in the 70's F but with a dip to the low 60's on Thursday as a cold front with rain passes through the region.
Thrips populations and TSWV risk At the moment the second post-winter adults are projected to peak around the first week of May. If things warm up significantly that generation may peak a few days earlier. Currently we don't have any reports of TSWV activity in overwintering hosts and with the very low thrips populations now, the overall risk is low. Our best guess at the moment is that we won't see significant thrips/TSWV activity in tomato until the third generation this year, which will be the first one to target, depending on whether TSWV has appeared, but please speak to your local UCCE adviser for more specific advice if you are concerned.
Resistance-breaking TSWV Strains of TSWV with the ability to overcome SW5 resistance are now established in the San Joaquin Valley and you should expect to see them throughout in the Central Valley in the near future. Do not assume that SW5 varieties will be able to escape TSWV damage without additional disease management practices. Our advice is to target early generations of thrips entering tomato (see above) and, where possible, to rogue out infected plans showing symptoms of TSWV early in the season. Remember, the impacts of TSWV are much smaller in plants infected after fruit set, so the aim should be to delay infection as much as possible, to avoid economic impacts.