- Author: Neil McRoberts
General Outlook The 2022 thrips season is upon us. 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 and all in all it has probably been a reasonably good year for thrips survival as pupae in the soil over the winter. 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 on Saturday) 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 Merced monitoring site, the current projection is for generation 1 adults to peak around March 24, with generation 2 egg hatch peaking in mid April and generation 2 adults peaking at the end of the first week 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.
- Author: Neil McRoberts
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 low 90's highs is expected by the 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 behind last year and roughly 12 days ahead of the 30-year normal.
Population projections Generation 3 post winter adults are expected to peak in the next day or two. Generation 4 adults are currently projected to peak around June 25th. 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.
Merced represents the northern edge of the area where SW-5 resistance breaking strains have been found in previous seasons in the San Joaquin Valley. 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.
- Author: Neil McRoberts
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 Merced 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 peaking right about now and adult numbers peaking at the end of the first week of May. 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 weeks 2 or 3 of May to suppress generation 3 thrips, which could be carrying TSWV.
- Author: Neil McRoberts
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 for the usual 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 Merced area, 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 have been found regularly for the last couple of seasons not too far south of your area.
Immediate outlook: Planting is getting underway, or has already happened. The first post-winter generation of adults is peaking right about now. The next peak in egg hatch is predicted for the third week in April and the peak of the second generation of adults at the start of the second 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, Merced County is 8 days behind 2020, at the same stage as 2019 and about 10 days ahead of the 30-yr norm.
- Author: Neil McRoberts
General situation: Things have warmed up recently. Our reference weather station for Merced is running about a week ahead of the last of year and a whole 12 days ahead of the 30-year average for heat accumulation, so far this season. We're into day 2 of a 4 day mini heat wave and that is sure to speed up thrips development. Things are set to cool off again slightly toward the end of the 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 31st, Generation 4 will peak on June 24th, and Generation 5 on July 15th. 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: We haven't had any reports of TSWV in the central San Joaquin Valley yet this season, but with crops well established and 2 to 3 generations of thrips probably now active since the winter, it's possible that any TSWV that over-wintered in weeds will have had the opportunity to start to move into crops. Although we've never had a detection of resistance-breaking TSWV as far north as Merced Co., Resistance-breaking TSWV has already been found further south in the Valley this season. In the long-term, spread of resistance-breaking strains is a concern. 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.
