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 high 80's to mid 90's F - perfect conditions for thrips development.  Late-planted crops could have a long way to go before flowering and fruit set, which is when the threat of serious yield loss from TSWV decreases.  The take-home is that with thrips activity certain to increase and crops relatively late, the risk of damage from TSWV could be high if the virus shows up in the near future.

Thrips generation timing We have extended the projections out to the end of July.  Generation 3 adults are projected to peak in the next 5-6 days.  Generation 4 will peak in the last week of June, with Generation 5, peaking around the third week of July.  If you are planning to apply treatments to control thrips/TSWV, the next 4-6 weeks will be the period that will provide the best result for the investment.  Since reported TSWV levels across the area are low, suppression of Generation 4 with treatments applied soon will delay the development of TSWV and allow crops a chance to grow past the most vulnerable period. 

General situation With the cool, wet spring crops and thrips alike are somewhat behind their usual schedule. Temperatures over the coming week to 10 days will start to climb and we will see mid 90's F days around mid-week, with temperatures in the low to mid 80's F the rest of the time.  Combined with an absence of prolonged rain, this pattern should see thrips development accelerate.  There is a possibility of scattered thunderstorms and rain showers over the next 10 days, but it's not clear at the moment if the low pressure area that would cause those will track across northern California.

Thrips generation timings  We have extended the projection interval out to the end of June.  The current projection shows generation 2 egg hatch peaked around mid April and generation 2 adults will peak around May 9th. We are currently projecting generation 3 adults will peak in the first week of June, with generation 4 adults possibly peaking right at the end of June.  So far this season TSWV incidence is still low so generation 2 adults probably do not represent a high risk of spread of the virus.  Remember, controlling thrips numbers early in the season delays the spread of TSWV and gives crops a chance to get past the most susceptible stages, pre-flowering, before the virus incidence begins to increase.  If you're planning to invest in thrips treatments this season, treatments will be most cost-effective if applied to control generation 3 or possibly generation 4.  Treatments can be scheduled from now onward through the end of June.

Update on resistance-breaking TSWV  So far, resistance breaking strains of TSWV have only been detected in Fresno Co, not in the upper San Joaquin Valley, but we know from surveys this year that the resistance breaking strains did over-winter, so there are likely to be some further outbreaks this year, most likely close to the areas where they occurred last year.  We will be providing updates as the season progresses.  If you want more information about the situation, contact your local UCCE adviser.

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 February 21st and adult numbers peak around March 27th.  Our current projection is showing generation 2 egg hatch around April 21st and generation 2 adults to peak around May 9th.  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.

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 is expected to peak on 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.