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.

Thrips populations and TSWV risk  At the moment the second post-winter adults are projected to peak around the end of the month, with the third generation peaking around May 30th.  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 in tomato 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.

Resistance-breaking TSWV  Strains of TSWV with the ability to overcome SW5 resistance are now established in the San Joaquin Valley and you should expect to see them throughout in the Central Valley in the near future.  Do not assume that SW5 varieties will be able to escape TSWV damage without additional disease management practices.  Our advice is to target early generations of thrips entering tomato (see above) and, where possible, to rogue out infected plans showing symptoms of TSWV early in the season.  Remember, the impacts of TSWV are much smaller in plants infected after fruit set, so the aim should be to delay infection as much as possible, to avoid economic impacts.

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 mightsee our first 90+F days around mid-week, although mid to high 80's F are possibly more likely  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 in the week ahead. 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 peaked around March 25th.  Our current projection is showing generation 2 egg hatch around April 19th and generation 2 adults to peak around May 8th.  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.