General situation: We're a little bit late getting the clock started this season, but here is the first post of the 2021 thrips/TSWV risk evaluation.  The aim is to give an update on a roughly 7-10 day interval until the end of June and then we'll take a look how the season is shaping up and most likely, reduce the frequency until harvest starts.
It's no secret that we've had another dry winter and spring.  There has been enough rain a flush over-wintering weeds, some of which may act as sources for TSWV, but the soil has been dry enough that over-winter survival of thrips pupae was probably on the high side.  Overall, things are set up so that we could see relatively large thrips populations early in the season this year.

We finished last season with still no sign that SW5 resistance-breaking TSVW strains had migrated to, or emerged in, the Kings County, so we're assuming that we're starting this season with no resistance breaking strains.  However, please keep an eye on any varieties carrying SW5 resistance and report any symptoms that might be TSWV to your UCCE local adviser so that we can stay on top of the situation.  Resistance breaking strains are widespread just a bit to the north in Fresno County so be aware of the possibility that they will show up in your area.

Immediate outlook:  Planting is underway or for some may have already been completed.  The first post-winter generation of adults peaked  2 or 3 days ago. The next peak in egg hatch is predicted for April 14th and the peak of the second generation of adults at the start of the first week in May.  Based on experience, we don't expect these two generations of thrips to be carrying much TSWV, but local hostspots could happen.  Based on temperatures so far this year, as far as thrips are concerned, Kings County is 3 days behind 2020, 5 days ahead of 2019 and about 1 day ahead of the 30-yr norm.

General situation:  Things have warmed up recently. Our reference weather station for Kings is running about 2 days ahead of last year and 2 days behind the 30-year average for heat accumulation, so far this season; in other words, unlike some counties further north Kings seems to be having a more or less normal year up till now for heat accumulation.  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 30th, Generation 4 will peak on June 21st, and Generation 5 on July 10th.  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: Fresno Co. is the hotspot for development of resistance breaking TSWV. We have already seen TSWV in some fields in that county this season 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.

General situation  We are firmly into the 2020 season and the weather is starting to settle into its summer pattern. According to the data from our reference weather station Kings Co is running almost exactly on its 30 year average heat accumulation.  A high in the upper 90's is forecast for Thursday with temperatures building to that peak and then declining again slowly.  That sort of temperature pattern will certainly accelerate thrips development so we might see some changes in predicted dates for generations as we pass through the next 2-3 weeks.

Thrips generation timings According to the degree-day projection, we are just past the peak for generation 2 (May 4th)  Unless you are seeing early TSWV symptoms, or consider crops to be at high risk, it's unlikely that generation 2 will be carrying much virus, but if you are concerned about early attack please contact a UCCE adviser to discuss your situation.  Generation 3 adults are predicted to peak on 5/29 (although, with hot weather on the way this might come forward a few days), with generation 4 following on June 20th.  Those two generations are the ones we would typically expect to be carrying the first significant levels of TSWV.  TSWV has been detected to the north in Fresno Co. in processing tomato, so if you're considering using insecticides against thrips to control TSWV, the next month is likely to be the most cost-effective time to make the applications.  Please contact your local UCCE adviser if you want to discuss the specifics of your situation.  The current projection runs until July 1. We'll be extending the projections this week and posting another update in 7-10 days.

Special Note: SW-5 resistance breaking strains of TSWV have been detected at multiple sites in Fresno Co in the last week or so.  Although we haven't yet seen issues with resistance-breaking strains as far north as Merced, be aware that these strains of the virus are out there and likely to spread over time.  If you see suspicious symptoms in SW-5 varieties please let your local UCCE adviser know.  We can arrange for samples to be collected for testing.

Hi.

We've been a bit slow getting the thrips risk and TSWV updates up and running this year.  We hope you are all safe and well.  We also want to say thank you to everyone involved in food production and agriculture in general for keeping the food chain flowing during the COVID-19 epidemic.

Current outlook After a warm, dry winter we're expecting thrips pupal survival over the winter to have been high and the numbers to pick up quickly.  The recent late season cold/rain system that passed through over the weekend will have checked them somewhat.  Based on the Davis weather station, we're currently projecting generation 1 adults to peak in the middle of April, with generation 2 in the first week of May and generation 3 in the last week of May.

Generally, generation 1 doesn't present much of a risk for carrying TSWV into processing tomato.  In recent years, TSWV hasn't been present until generation 3 or 4, but we will gather up status report before our next update in case there's any virus out there early this year and action is needed on generation 2.

As ever, if you're seeing high thrips counts or obvious signs of TSWV we'd like to hear from you via your local UCCE adviser.  Best wishes for a good growing season and for as much normality as possible in these difficult times.