- Author: Neil McRoberts
General outlook After a brief spike in temperatures over the last few days, with highs in the low to middle 80s F, a more unsettled and cooler pattern will return for the coming week, including a chance of localized rain showers on Saturday. Highs will likely be in the low 80s F once Saturday's cooler front has passed through. Overall temperatures will be adequate for thrips development and we expect to see populations continue to develop.
Thrips/TSWV situation We are expecting generation 2 adults to peak in the next few days. If temperatures stay on track generation 3 will likely see its peak adult numbers in the first week of June. We have now had confirmed TSWV cases in the southern San Joaquin Valley and the Sacramento Valley, so this seems like a year when targeting generation 3 will give useful benefits. Generation 3 juveniles will be feeding and developing over the rest of May, so treatments applied in the second half of the month will have a chance to prevent infected adults from spreading the virus to new hosts. If you are considering investing in a thrips treatment this season, the second half of May appears to be a good time to make that treatment.
- Author: Neil McRoberts
General situation with apologies to everyone, we're a little late getting underway this season - a combination of a family health emergency and international travel to an epidemiology workshop. Temperatures will start rising from tomorrow morning, peaking around 80F on Thursday before settling into a run of days where the maximum will be in the low to mid 70's, with no rain on the forecast.
Thrips development The degree day model is showing that Generation 2 peak egg hatch will be occurring this week. Based on that, and the 30 year temperature accumulation curve for this time of year, the peak adult activity from that hatch would be expected around May 2nd. Knocking Generation 2 back would be the earliest intervention that would be likely to have an impact on TSWV spread, but it might be more effective to hold off until Generation 3 is active. The decision will depend on a few other circumstances. Consider targeting Generation 2 if: the location of the crop has a history of TSWV; you are already seeing thrips on sticky cards; there are early reports of TSWV in the area. If thrips numbers remain low and other risk factors are not indicating high risk, consider waiting until Generation 3 before investing in control. Generation 3 adults are projected to peak in the first week of June, so treatments scheduled in the last week of May would be appropriate. We will update the dates in response to the weather over the next 4 weeks.
- Author: Neil McRoberts
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.
- Author: Neil McRoberts
- Author: Neil McRoberts
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.