- 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 the Merced area 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 mid 80s to low 90s F which means that thrips will be fully active. Generation 3 adult numbers are projected to peak in the next couple of days, with generation 4 on June 24. 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 low 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 4/29.
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 (5/30) and late June (6/23) 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.
- Author: Neil McRoberts
Welcome to the UC Davis Western Flower Thrips generation time projections for the Merced area for 2015. The phenology clock is telling us that overwintering adults are present at this time. Thrips degree-day accumulations are above the 30 year average so far this year and we're projecting the peak dates for the first two post-winter adult generations at April 5th and May 14th. Generally, TSWV doesn't begin to increase until the third and fourth generations of thrips are present. We'll be posting regular updates on the situation from now on.
- Author: Neil McRoberts
General Situation Maximum temperatures over the coming week are forecast to be in the mid 90's F, which is ideal for thrips development. TSWV has now been reported in all areas of the Central Valley including Merced County so a precautionary approach is recommended to avoid yield loss, particularly in late planted crops and varieties that do not carry the SW5 gene for TSWV resistance.
From now, through to the end of the cropping season, thrips generation peaks will be three to four weeks apart. Crops which do not carry the SW5 gene for TSWV resistance should be protected until fruit set is complete, bearing in mind that a new wave of thrips adults which can spread the virus will build up and decline roughly on a three to four week cycle.
Generation 3 was projected to peak on May 21st and will have produced eggs and a new generation of larvae. Immediate spraying will reduce the number of these juveniles and reduce the numbers of adults in Generation 4.
Generation 4 is projected to peak on June 13th Adults from this generation will already be appearing. Spraying between now and June 13th will knock down the number of adults which are able to breed and lay the eggs which will give rise to generation 5. Because there is some TSWV present in the region generations 4 and 5 adults may well contain infected adult thrips that will spread the virus. Concerted effort to reduce these generations will limit the effects of disease on late planted crops.
Generation 5 is projected to peak on July 5th. Depending in crop development, this may be the last generation of thrips for 2014 that can cause serious damage to processing tomato because most crops should be past the very sensitive stage by that time. Particularly on late planted and late developing crops, consider maintaining an active control program for thrips through to mid July.
