General situation  After a slow, late start to the season, summer has finally arrived and is staying. Kings will see temperatures building over the next few days and settling into an extended period with 100+ highs, including several days with highs over 110.  All that heat will really accelerate thrips development and increase their activity. 

Thrips generations and TSWV  We have extended the population projection out to September 1.  Generation 5 adults should peak aroundJuly 18, with generation 6 following around August 5.  Thrips numbers have been low across much Central Valley until now, but TSWV is relatively easy to find in most areas, albeit at relatively low incidence.  Resistance-breaking strains of TSWV are now ubiquitous in the San Joaquin Valley, so varieties with the SW-5 gene will need protection in situations where thrips pressure is high.  

In normal seasons most of the crop would be far enough along that our main concern would be generation 4, but there are quite a few late-planted fields and generations 5 and 6 could bring in TSWV before these crops are big enough to shrug off virus strikes.  Late-planted crops might require additional protection this year, particularly in locations with a history of TSWV damage.

General Outlook Well, here we are, the 2022 season is open for business.  The first half of the winter was wet and cold, but since the turn of the year, we have seen next to no precipitation in the region.  Temperatures have been more or less normal for the time of year.  All in all it has probably been a reasonably good year for thrips survival as pupae in the soil over the winter and unless we get some serious cold wet weather to round off the spring the prospect is that thrips numbers are likely to start building quickly over the next couple of months.  The next 10 days or so will see changeable weather with a cool weekend and start to next week (with a small chance of rain showers) giving way to a run of three or four days with temperatures in the high 80's.  Those kinds of temperatures will accelerate thrips development.

Population projections  Based on temperatures experienced at the Belridge monitoring site, the current projection is for generation 1 adults to peak around March 22, with generation 2 egg hatch peaking in mid April and generation 2 adults peaking on or around the first of May.  Unless you are in an area with a history of early TSWV infections and you suspect that the virus is already present in weeds or other crops close by, the chances are that the first couple of generations of thrips will be relatively free from virus and usually do not pose a serious threat to new tomato plantings.  TSWV has been spotted in lettuce in Fresno County so be aware that there are possible sources of TSWV which could mean that we see the virus in tomato early this season.  If in doubt about treatments and the current risk situation, contact your local UCCE adviser.

General outlook  A week of 100+ F daily maximum temperatures and warm nights will give thrips development a boost over the next week.  A gradual return to mid 90's highs is expected by the second week of June.  The current mini heat wave won't be enough to cause any significant mortality in thrips.  Degree day accumulation for thrips this season is about two days ahead of last year and roughly one day ahead of the 30-year normal.

Population projections Generation 3 post winter adults peaked in the last day or so.  Generation 4 adults are currently projected to peak around June 19th.  These two generations are the first that are likely to have significant levels of TSWV in them, so any plans to apply insecticide specifically to control thrips and suppress TSWV should be scheduled sometime in soon.  We've seen some TSWV already in a few areas.  Levels are generally low (below 1%), but there are a couple of hot spots that show there has been some early secondary spread of the virus within the crop. Secondary spread would be indicated by seeing short runs of two or three plants with symptoms clustered together. Under these circumstances treatment to suppress further spread is recommended. If you are not seeing any signs of TSWV in your area you may want to consider delaying treatment and re-assessing the situation for generation 5.  If you want further advice on management options for your situation please contact your UCCE advisor.

We are now finding SW-5 resistance breaking strains routinely in Fresno and Kings counties.  These strains are now the dominant type in this region and relying on SW-5 resistance to avoid TSWV damage is not recommended.  SW-5 varieties that have other favorable agronomic characteristics can still be used as part of an IPM approach for disease control.

Please report any unusual virus-like symptoms to your local UCCE adviser.  In addition to TSWV there are a number of other viruses that might show up in tomato.  Most of these will have minimal effects on yield in processing crops, but we are always on the look out for reports of viruses to help get a complete picture of what's happening across the region.