- 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 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.
- 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. With some planting still in progress and many crops at an early stage of growth we're already seeing some TSWV in Fresno Co., so we'll be keeping a close eye on the situation this season. Please contact your UCCE local adviser if you see TSWV symptoms in your crop.
Thrips and TSWV situation The projection model is showing generation 2 egg hatch peaked a few days ago and adult numbers for generation 2 will peak right at the end of April. Generation 3 adults are likely to peak in the last week of May.
Low risk situations
If you don't know of any local sources of TSWV and crops have just been planted it might be worth delaying treatment until the first half of June. This would be our regular recommendation in typical years. The risk is that it will allow generation 2 and 3 adults to breed and lay eggs, but if there are no local sources of TSWV the chances are that delaying thrips treatments to target generation 3 will be sufficient to delay TSWV from building up and causing severe damage.
High risk situations
If you do have local sources of TSWV, if you've planted early and are worried about early entry of TSWV to your crop, or if you do not want to take the risk of allowing generation 2 to bring TSWV into the crop, consider treatments in the first half of May. Treatments around this time will target generation 3 juveniles developing on plants and also the tail end of the generation 2 adults.
- 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 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.
- Author: Neil McRoberts
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.
- Author: Neil McRoberts
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.