- 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 Upper San Joaquin Valley, 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.
Immediate outlook: The first transplants in the region are either in the ground by now, or soon will be. The first post-winter generation of adults peaked 2 to 3 days ago. The next peak in egg hatch is predicted for April 18th and the peak of the second generation of adults at the end 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, the eastern San Joaquin County is 8 days behind 2020, 1 day ahead of 2019 and about 13 days ahead of the 30-yr norm.
- Author: Neil McRoberts
General situation: Things have warmed up recently. Our reference weather station for Eastern San Joaquin is running about a week ahead of the last couple of years and 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 28th, Generation 4 will peak on June 22nd, and Generation 5 on July 14th. 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 northern 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 in the northern counties, Resistance-breaking TSWV has already been found in the southern San Joaquin 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.
- Author: Neil McRoberts
General situation Planting is well under way, if not complete for the main season crop. The weather is starting to settle into its summer pattern. According to the data from our reference weather station the area is running slightly ahead of the 30 year average. A high in the mid 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 just past the peak for generation 2 adults in the last 5 days. 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 in the third week of June. Those two generations are the ones we would typically expect to be carrying the first significant levels of TSWV. The current projection runs until July 1. We'll be extending the projections this week and posting another update in 7-10 days.
- Author: Neil McRoberts
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 first week of June.
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.
- Author: Neil McRoberts
Weather outlook: After further atypical cool, showery weather over the last week or so, the forecast for the next ten days shows a more settled period of dry weather with partial cloud cover and daytime highs gradually increasing towards 90F. Thrips population development can be expected to be steady over this period.
Thrips population timings: In our last update on 4/16 we projected Generation 3 adults to peak on June 5th and Generation 4 to peak on June 29th. Despite the period of cool weather projections for eastern San Joaquin county have remained more or less unchanged: Generation 3 is projected to peak on June 5th (as before) and Generation 4 on June 30th (one day later than last update). We are still not hearing reports of any TSWV in the area, and together with the delay in thrips development, the overall risk level in the upper San Joaquin Valley is low. Depending on crop development stage we recommend targeting either Generation 3 or Generation 4 for any intended thrips treatments. Later planted crops may still be at early, vulnerable growth stages as Generations 3 and 4 emerge; stay on top of the situation and check in with your UCCE adviser to find out if TSWV is being reported as the season progresses.