- 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 middle 70s 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 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 70's to 80F, reaching the mid 80'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 14 and Generation 4 adults will peak around July 7. 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
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 in the low 80sF on Thursday before settling into a run of days where the maximum will be in the 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 6th. 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. Eastern San Joaquin 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 are peaking right now. Generation 5 adults should peak around July 30, with generation 6 following around August 21. 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.
