- Author: Neil McRoberts
Daytime high temperatures will be in the high 70's to mid 80's over the next few days before things cool off a little on Friday, when the San Joaquin valley is forecast to see some rain. These temperatures are ideal for thrips development and the season has a little ahead of the rate we would expect based on the 30-year average temperatures; the second post-winter generation of adults will peaked around 4/30, with the third generation expected to peak around 5/31. So far we haven't had reports of TSWV outbreaks in the area, so there's a good chance to stay on top of the TSWV risk if you are planning to use an insecticide to suppress thrips development. With low virus levels in the area, treatments applied to knock down the second thrips generation (in late April) or the third generation (in late May) will likely have a good effect. Overall the immediate TSWV risk generally low.
- Author: Neil McRoberts
This is the first update on western flower thrips for 2016.
It has been a warm winter so far. Warm weather means faster thrips development, so this year might see the optimum treatment period for thrips in processing tomato occurring slightly earlier than normal (whatever normal means these days...). In the eastern portion of the Sacramento delta the first generation thrips egg hatch probably took place in mid February and peak adult numbers for that generation are projected in about 14 days from now. The second generation egg hatch will happen around the 12th of April. The cooler, wet weather forecast for the next few days is likely to slow development and increase thrips mortality so despite the warmer general conditions thrips numbers might not build too quickly, at least in the immediate future. So far we have no reports of TSWV so risk of damage is currently low.
- Author: Neil McRoberts
Which crops will benefit from thrips treatment?
Our last update indicated that thrips pressure was building and with some TSWV already out there, it was important to treat for thrips now to prevent TSWV really taking off. We scouted several crops in western Fresno Co. last week and generally found a low level of TSWV in non-sw5 varieties. Early-planted crops are already well into fruit filling and are unlikely to benefit from a thrips treatment at this time. However, late planted crops that are only just flowering or are pre-flowering are still at the most sensitive stage for TSWV infection. Any thrips control planned for this time should focus on late planted crops that have not reached mid fruit set.
- Author: Neil McRoberts
General Outlook
Post-winter thrips numbers are building up now. This week the second generation post-winter is projected to peak. Following the pattern of the last couple of years for May, TSWV incidence in Eastern San Joaquin Co. is still low this year which means that there is still an opportunity to get ahead of the disease by suppressing thrips numbers.
Projections and thrips management
The weather over the coming week is predicted to have highs in the high 70s to low 90s F which means that thrips will be fully active. Generation 3 adult numbers are projected to peak around June 4, with generation 4 on June 28. The build up in thrips numbers over the next 3 to 4 weeks will be very fast. For this reason suppressing these generations will be important to staying ahead of TSWV and avoiding economic damage in processing tomato. Any insecticide treatments planned for thrips control and TSWV management should be targeted at these two generations. Later treatments are likely to be much less effective. Immediate action is recommended.
Protection of sw-5 resistance
TSWV resistant varieties rely on the sw-5 resistance gene. The availability of effective TSWV resistance in processing tomato varieties is a huge bonus for the industry and a valuable shared resource that needs careful management. Growing sw-5 varieties without the benefit of insecticide protection to suppress thrips increases the chances of resistance-breaking strains of the TSWV virus developing. The larger the acerage of sw-5 varieties grown without insecticide protection, the greater the risk of resistance-breaking developing. For this reason, we strongly recommend that sw-5 varieties are treated like susceptible varieties and, if at all possible, you do not rely on the resistance alone to manage TSWV.
- Author: Neil McRoberts
A cool front will move through the region over the next 24 hours with a reasonable chance of rain. Temperatures over the next week are likely to see highs in the high 70'sF to mid 80'sF, meaning that thrips development will be steady. The second post-winter generation of adults is emerging around this time and will peak around 4/30.
Currently, there are no reports of serious TSWV outbreaks and virus levels appear to be generally low - as is usually the case at this time of year. The third and fourth generations of adults are projected to peak at the end of May (5/31) and late June (6/25) respectively. Control focused on these generations is likely to keep TSWV levels below economic damage. Late planted crops will be more sensitive to TSWV so extra care should be given to protecting any crops which have not reached flowering by late May.
