- Author: Neil McRoberts
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.
- Author: Neil McRoberts
Dixon Area General situation It has been an up and down start to the year for thrips development. Through February the relatively dry winter, and somewhat warm start to the year in the San Joaquin Valley meant we were running ahead of the 30 year average for degree day accumulation. The last couple of rain events have slowed things down, but we are still ahead of the long-term average. Temperatures in the week ahead are predicted to be in the mid 60's F to mid 70's F, with the chance of further rain in the second half of the week.
Dixon Area Thrips populations and TSWV risk At the moment the first post-winter adults are projected to peak around the end of the week, with the second generation peaking around May 20th. If things warm up significantly those two generations may peak a few days earlier. Currently we don't have any reports of TSWV activity in overwintering hosts and with the very low thrips populations now, the overall risk is low. Our best guess at the moment is that we won't see significant thrips/TSWV activity until the third generation this year, which will be the first one to target, depending on whether TSWV has appeared, but please speak to your local UCCE adviser for more specific advice if you are concerned.
Hollister/Gilroy Area General situation Similar to elsewhere, it has been an up and down start to the year for thrips development. Through February the relatively dry winter, and somewhat warm start to the year in the Pacheco area meant we were running ahead of the 30 year average for degree day accumulation. The last couple of rain events have slowed things down, but we are still ahead of the long-term average. Temperatures in the week ahead are predicted to be in the mid 60's F to low 70's F, with the chance of further rain in the second half of the week.
Hollister/Gilroy Area Thrips populations and TSWV risk The first post-winter adults peaked around the end of the March, with the second generation expected to peak in early May. Assuming things warm up and hit a stable pattern this month we can expect the third generation toward the end of May or first week in June. Currently we don't have any reports of TSWV activity in overwintering hosts and with the very low thrips populations now, the overall risk is low. Our best guess at the moment is that we won't see significant thrips/TSWV activity until the third generation this year, which will be the first one to target, depending on whether TSWV has appeared, but please speak to your local UCCE adviser for more specific advice if you are concerned.
- Author: Neil McRoberts
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.
- Author: Neil McRoberts
Dixon area
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.
Gilroy/Hollister area
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.
