Dixon area general outlook After the extended cool spring, it looks like we have settled into typical summer weather for the Central Valley. Temperature projections for the next 7-10 days are in the mid 90's to high 90's F - perfect conditions for thrips development. So far there are no reports of TSWV on pepper in the area, but with delayed planting as a result of the extended spring rains, crops will be susceptible to damage for some weeks to come.
Gilroy/Holiser area general outlook There are no reports of TSWV in the Gilroy/Holister area yet. In common with other areas of northern California, planting was delayed this year as a result of the wet spring and crops are still relatively small. Highs will be in the low to mid 80's F across the area over the next few days and thrips numbers are building up steadily.
Thrips generation timing We have extended the projections out to the end of July. Generation 3 adults in both areas will probably peak this week. Generation 4 will peak in late June or early July, with Generation 5, peaking in the second half of July. If you are planning to apply treatments to control thrips/TSWV, the next 4-6 weeks are a critical period for getting effective control on thrips populations. Since reported TSWV levels across both areas are low the immediate risk is not high, but action now will suppress Generation 4 and limit the spread of TSWV into and within pepper crops. On the current schedule, an early to mid July treatment would impact Generation 5. We will issue further updates over the next few weeks.
General situation Welcome to our updates on Western Flower Thrips development for 2017. The cool wet winter and early spring mean that degree day accumulation for thrips is currently running behind the 30 year average. The wet weather and saturated soils are also likely to have caused higher than normal mortality for thrips pupae, so we're expecting numbers to be low, at least to start with this season - but let us know if that's not what you're seeing!
Projected thrips development As in previous years we're using January 1st as our start date for the biological calendar. Assuming that's approximately correct, the first post-winter generation of eggs probably hatched around March 12th and adult numbers will peak around April 9th. Our current projection is showing generation 2 egg hatch around April 30th and generation 2 adults to peak around May 17th. Generation 2 is the very earliest we would expect to see thrips starting to move TSWV around. Again, let us know (through your local UCCE adviser) if you're seeing TSWV early in the season.
Resistance breaking TSWV Last season there were a number of confirmed cases of resistance-breaking(RB) strains of TSWV in mostly fresh-market tomatoes, but also in a processing tomato field, in the San Joaquin Valley. The RB strains of the virus that can overcome (break) the resistance conferred by the SW-5 gene that is now widely used in fresh-market and processing varieties. Based on last season's observations the RB strain was quite localized (Cantua Creek, Firebaugh and Rt. 198), but we are keeping the situation under scrutiny and will be surveying crops this season to assess how things are developing. We can report that we have detected the RB strain in weeds (sowthistle) with tomato spotted wilt symptoms from Cantua Creek and Rt. 198; thus, the RB strain has been able to survive the winter. We'll keep you posted on what we're seeing through these updates. If you want to know more about the situation contact your local UCCE adviser.
The first generation of thrips post winter peaked around March 31. We are currently expecting peak egg hatch for generation 2 to be happening right now, and generation 2 numbers to peak around May 8th. The forecast temperatures over the next 3 days are ideal for thrips development but if the forecast cooler and wet weather occurs on Friday/Saturday development may be delayed will be delayed and there may be some thrips mortality. The early season overall is running slightly ahead of the 30 year average and we are expecting the third generation of adults to peak in the first week of June. So far we have no reports of TSWV in other susceptible crops in the area so immediate risk of infection is low. If you are planning to use an insecticide to suppress thrips numbers, immediate action will impact generation 2. Later applications (in mid to late May) will impact generation 3. Contact your PCA or local UCCE adviser if you would like further advice on spray timing.
The first generation of adult thrips post winter is peaked on March 8th and the second generation will peak on 4/25. Immediate action will help to suppress this generation, but TSWV risk is currently low another option would be to focus early season treatment on generation 3; adults of generation 3 will peak on May 31. The forecast temperatures over the next 3 days are ideal for thrips development but if the forecast cooler and wet weather occurs on Friday/Saturday, development may be delayed and there may be some thrips mortality. The early season overall is running slightly ahead of the 30 year average. We have no reports of TSWV in the area and the immediate risk of TSWV is low.
This post covers two separate regions where peppers may be subject to damage from TSWV - in the Dixon area along the Yolo/Solano Co line and in the area between Gilroy and Hollister around the Santa Clara/San Benito Co line.
The first generation of thrips post winter are mainly still maturing and we are projecting the peak of adult numbers by around March 26th. We are currently expecting peak egg hatch for generation 2 around April 20th but if the forecast cooler and wet weather does occur development will be delayed and there may be considerable mortality and thrips numbers will be held in check somewhat. So far we have no reports of TSWV in other susceptible crops in the area so immediate risk of infection as direct seeding gets under way is low.
The first generation of adult thrips post winter is peaking now and we are projecting the peak of egg hatch for generation 2 around April 6th. The second generation of adults will peak sometime around April 29th. As with projections for other areas and other crops if the forecast cooler and wet weather does occur, thrips development will be delayed and there may be considerable mortality. If the cool wet weather persists thrips numbers will be held in check somewhat. The immediate risk of TSWV is low.
Welcome and General Outlook
Welcome to the thrips/TSWV risk projections for pepper crops in the Yolo/Colusa region. This mini-blog is associated with the online thrips projections that can be found at http://ucanr.edu/sites/TSWVfieldriskindex/Thrips_projections_in_peppers/
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Post-winter thrips numbers are building up now. The second generation post-winter peaked on May 10 and two further generations are due by early July. TSWV incidence in pepper in Yolo/Colusa is low at the moment but the virus has been detected in one or two crops in the Colusa area. The virus multiplies quickly in infected crops so this is an important time of year to take action to manage the disease.
Projections and thrips management
The weather over the coming week is predicted to have highs in the mid 70s to the mid 80s F which means that thrips will be fully active. Generation 3 adult numbers are projected to peak on June 14, with generation 4 projected on July 7. The build up in thrips numbers over the next 2 months will be moderately fast and these generations are the ones which will really spread any TSWV that is present now. For this reason suppressing thrips now will be important to staying ahead of TSWV and avoiding economic damage. 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 tsw resistance
TSWV resistant pepper varieties rely on the tsw resistance gene. The availability of effective TSWV resistance in peppers is a huge bonus for the industry and a valuable shared resource that needs careful management. Growing tsw 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 tsw varieties grown without insecticide protection, the greater the risk of resistance-breaking developing. For this reason, we strongly recommend that tsw varieties are treated like susceptible varieties and, if at all possible, you do not rely on the resistance alone to manage TSWV in pepper.