General situation: The main season crop is in the ground and developing well as we head into high summer.  The next 10 days is forecast to range from the high 70's to mid 90's, which is ideal conditions for thrips to develop.

Resistance breaking strains of TSWV:  Resistance breaking (RB) strains of the virus have now been confirmed across the whole range of tomato production in the Central Valley so SW-5 varieties are no longer guaranteed to shrug off any early infections.  After a few years of relatively simple TSWV management we're moving back into a period when a whole-system, IPM, approach will be needed to keep the virus at bay.

Thrips projections and management: We've extended the degree day model out to the end of July.  Currently, the model is showing us that we're probably in the transition from the second to third post-winter generation.  Generation 3 adults are peaking, with generation 4 adults following in about 3 weeks.  These are the two key generations of thrips to control to prevent damage to the crop; growers who are considering investing in thrips control treatments are likely to see the biggest impact if treatments are applied any time from now through the end of June.  We have had a few reports of scattered TSWV in crops and the aim now should be to stop thrips from spreading the virus from those few initial infections.

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 Modesto monitoring site, the current projection is for generation 1 adults to peak right around now, with generation 2 egg hatch peaking around April 10th and generation 2 adults peaking in the last few days of April.  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.

General outlook  A few 100+ F daily maximum temperatures and warm nights will give thrips development a little boost over the next week.  A gradual return to low-to-mid 90's highs is expected from now until second week of June.  The current mini heat wave won't be enough to cause any mortality in thrips.  Degree day accumulation for thrips this season is about two days last year and roughly 5 days ahead of the 30-year normal.

Population projections Generation 3 post winter adults peaked in the last few days.  Generation 4 adults are currently projected to peak around June 18th.  These two generations are the first that are likely to have any appreciable level of TSWV in them, so any plans to apply insecticide specifically to control thrips and suppress TSWV should be scheduled sometime in soon.  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.

We still have no reports of SW-5 resistance breaking strains in the mid San Joaquin Valley so crops carrying the SW-5 resistance to TSWV should see little effect of the virus again this season.  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.

General outlook We're heading into to a run of slightly warmer weather which will last about a week and accelerate thrips development.  Although we haven't heard of any TSWV in Stansilaus Co. so far, it has been reported in the southern San Joaquin Valley and the warm, dry winter may increase the risk of seeing disease early this season.

Thrips and TSWV situation The projection model is showing generation 2 egg hatch peaked about a week ago and adult numbers will peak in the last week of April.  Generation 3 adults are likely to peak in the first week to 10 days of June.  If you don't know of any local sources of TSWV and crops are not in the ground, or are just planted, it might be worth delaying treatment until mid June.  This would be our regular recommendation in typical years.  It would allow generation 3 adults to breed and lay eggs, but will catch juveniles developing from generation 3 eggs and suppress the spread of any TSWV that has come into crops with generation 3 adults.

If you do have local sources of TSWV, or if you've planted early and are worried about early entry of TSWV to your crop, consider treatments in the first couple of weeks of May to suppress generation 3 thrips, which could be carrying TSWV.