Weather outlook:  After further atypical cool, showery weather over the last week or so, the forecast for the next ten days shows a more settled period of dry weather with partial cloud cover and daytime highs increasing towards the mid 90'sF.  Thrips population development can be expected to be steady over this period.

Thrips population timings: In our last update on 4/16 we projected Generation 3 adults to peak on May29th and Generation 4 to peak on June 24th.  The period of cool weather has slowed development further, delaying the projected generation times by 2-3 days.  The projected peak date for Generation 3 is now June 3rd, with Generation 4 now projected to peak on June 25th.  We are still not hearing reports of any TSWV in the area, and together with the delay in thrips development, the overall risk level remains low.  Remember that we did find SW-5 resistance breaking strains of TSWV to the north in Fresno Co. earlier in the season, so be aware that SW-5 varieties may be vulnerable to attack this season.  Depending on crop development stage we recommend targeting Generation 4 for any intended thrips treatments if they have not already been made. Later planted crops might still be at early, vulnerable growth stages as  Generation 4 emerges; stay on top of the situation and check in with your UCCE adviser to find out if TSWV is being reported as the season progresses. 

Weather outlook  The next 10 days will see consistent warm, dry weather in the San Joaquin Valley. Highs in the upper 70's to high 80's and overnight lows in the mid to low 50's will allow steady thrips development, and we should see numbers starting to build up.

Generation peak timings  since our last update a couple of weeks ago our predicted peak date for generation 3 has moved forward by two days to May 29th, and generation 4 has also advanced by two days to June 20th.  If you are concerned about TSWV risk these are the two generations where control will have the biggest impact.  Knocking thrips numbers down while the populations are still relatively small and while the crop is still small enough to allow good penetration of sprays is a good tactic.  Keeping thrips under control at this stage also allows the crop to grow past the really vulnerable stage before and during flowering before there is much TSWV around and helps to reduce the yield impact if the virus does show up.  The UC IPM guidelines for thrips control can be found by following this link.  Further advice on treatments is available from your local UCCE adviser.

General situation After a dry and warmer weekend, the weather will return to a cooler, unsettled pattern next week, with temperatures in the mid 60's to low 70's and significant chance of further rain showers on several days.  This pattern will prolong the slow start to the season, with thrips developing relatively slowly at the forecast temperatures.  We have projected thrips development out to the end of June, based on current conditions. This takes in the first four generations of thrips and covers the period we would typically think of as the most critical for controlling thrips numbers.  Because we are projecting ahead by two to three months, based on relatively cool early season conditions, we can expect the projected dates for generations to peak to vary by a few days as we settle in to the summer season.

Specific details Generation 2 adults probably peaked a few days ago but a few will still be emerging.  Since there are no significant sources of TSWV this early in the season, thrips are not a risk at the moment.  We are expecting to see Generation 3 adult numbers peak around May 31^st with Generation 4 peaking around June 22^nd.  Given the slow start to the season, at this stage we would expect Generation 4 to be the key generation to target to suppress TSWV until the pre-flowering high risk period is past.  We will be actively monitoring the TSWV situation and will be posting updates, especially if anything happens to change our current advice.

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.  Average temperatures have been at, or above, 45F since the middle of January (although they 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 in the high 50's to low 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.