Hello. This is the first update for 2019 for the UC western flower thrips/tswv outlook for processing tomato.
General outlook As a reminder the base temperature we use for estimating thrips development is 45F. There was a string of days in the second week of January when average temperatures were above 45F, but things cooled off significantly when the atmospheric rivers started arriving in February, so we haven't had any significant accumulation of degree days for again until the last week or so. The 10-day outlook is for further unsettled weather with average temperatures slowly climbing into the low-to-mid 60's, but daily minimum's at, or below, the development threshold. The take home is that we're not expecting any sudden acceleration in thrips development soon. The relatively cool, wet soil conditions this spring also probably mean that there has been high mortality in over-wintering soil-borne thrips pupae, so initial numbers of thrips will be low. If you are seeing things different from this please let us know.
Development forecast We are currently running the projection model out to the end of April. The first 2019 generation of adult thrips is currently projected to peak around March 27th. We're expecting virus levels to be low in the first couple of generations (until thrips pick up tswv from infected weeds or there is initial infection in early tomato crops). Depending on when soil conditions allow planting to get underway it's hard to say at this stage of the season how early we'll see significant TSWV starting to appear; watch this space.
SW-5 breaking TSWV strains We have continued to track the spread of resistance-breaking TSWV strains. To date, all of the detections have been in the San Joaquin Valley, with nothing so far detected in the Sacramento Valley. We'll be posting a more detailed update in the near future.