- Author: Neil McRoberts
General situation After a slow, late start to the season, summer has finally arrived and is staying. Fresno will see temperatures building over the next few days and settling into an extended period with 100+ highs, with several highs in excess of 110 predicted. 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 around July 11, with generation 6 following around July 29. 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
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 mid to high 80'sF, reaching the mid 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 We have had a few sporadic thrips detections but no TSWV so far in Fresno county. There's a wide range of crop growth stages in the main planting areas, from stuff that has only gone in the ground in the last 7-10 days, up to crops that are bushing out well, and flowering is underway. The low thrips numbers and lack of TSWV 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 3 and Generation 4 adults will peak around June 25. 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 across the northern counties and canopies are filling out the beds nicely. The next 10 days is forecast to range from the low 80's to high 90's, which is ideal conditions for thrips to develop.
Resistance breaking strains of TSWV: Resistance breaking (RB) strains of the virus have been resident in Fresno county for several years. SW-5 varieties are no longer guaranteed to shrug off any early infections. After a few years of relatively simple TSWV management based on host plant resistance 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 three 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.
