- Author: Neil McRoberts
General situation After a slow, late start to the season, summer has finally arrived and is staying. Merced will see temperatures building over the next few days and settling into an extended period with 100+ highs. 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. It looks as though generation 4 adults peaked a couple of days ago. Generation 5 adults should peak around July 27, with generation 6 following around August 17. Thrips numbers have been low across much of the 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
General Situation After the wet winter and extended cool spring, the annual summer weather pattern finally seems to have established itself. Temperatures for the next 10 days will see daily maximum values in the low 80's F, reaching the low 90's by the first few days of June. Planting has been happening rapidly over the last 2-3 weeks and crops will pull away quickly with settled warm conditions.
Thrips and TSWV So far, thrips numbers have been low and we are not hearing reports of TSWV so far in this area This is all good, but we are concerned that the late planting times will mean that the pre-flowiering high risk period for TSWV will be extended this year. We are predicting that Generation 3 adults will peak around June 13 and Generation 4 adults will peak around July 5. Given the slow start and low leves of TSWV so far, unless there is a local source of TSWV, Generation 4 seems the more likely source for any significant chance for TSWV to spread around, and the more likely to pay off in terms of investment in thrips control. Contact your local UCCE adviser if you want to discuss options specific to your situation.
Resistance breaking TSWV Remember reistance breaking strains of TSWV are now widespread in the San Joaquin Valley, so varieties carrying the SW-5 resistance won't necessarily stand up on their own without thrips management if there are local sources of TSWV. At locations with a history of TSWV it's probably better to treat SW-5 varieties the same way as varieties without the resistance gene.
- Author: Neil McRoberts
- Author: Neil McRoberts
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 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 in transition from the second post-winter population to the third. Generation 3 adults will hit peak activity in the first week of June, with generation 4 adults following about 3 weeks later. 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.
- 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.
