A cool front will move through the region over the next 24 hours with a some 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 peaked around 4/20.

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 in late May (5/23) and mid-June (6/15) 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. 

Welcome to the UC Davis Western Flower Thrips generation time projections for the Fresno area for 2015. The phenology clock is telling us that overwintering adults are present at this time.  Thrips degree-day accumulations are running slightly ahead of the 30 year average so far this year and we're projecting the peak dates for the first two post-winter adult generations at March 26th and May 5th.  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.

General Situation Maximum temperatures over the coming week are forecast to be in the lmid 90's F, which is ideal for thrips development.  TSWV has now been reported in all areas of the Central Valley, especially in Fresno County.  The area around Huron in particular has some crops with relatively high disease incidence. Because of the relatively high disease pressure, 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 17th 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 9th.  Adults from this generation will already be appearing.  Spraying between now 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 will 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 June 30th.  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. However, generation 6 is projected to peak on July 20th.  Particularly on late planted and late developing crops, consider maintaining an active control program for thrips through to mid July.

General situation The situation remains unchanged since our last update on May 1st.  There are numerous reports of  TSWV symptoms in crops from Stanislaus Co down to Fresno and Kings Co's, particularly around the Huron area. The current risk in Fresno  Co  is high and we are recommending that growers who plan to use an insecticide program against thrips/TSWV take immediate action. The current mini heat wave will accelerate thrips development slightly and further bump up thrips numbers. 

If you are planning to use an insecticide program against thrips/TSWV this season, you should target the next generation of thrips (generation 3).  If it is not possible to arrange for treatment in time to catch generation 3, target generation 4. Delaying treatment until later in the season will be much less effective at preventing damage from TSWV.  Coordinated spraying across large areas has an additional effect on thrips populations because it makes it difficult for them to avoid treatment by migrating.

Generation 3 adults are projected to peak on May 18th, one day later than in our last update.  To check the development of  this generation of thrips you need to take immediate action.  If treatment cannot be scheduled in the next couple of days you should consider treatment to check generation 4.

Generation 4 adults are projected to peak on June 11th.  Sprays applied in the 14 day period before this peak date will check generation 4 and delay further population build up and TSWV spread.  Treatment in the 14 days immediately following the generation 3 peak date will also be effective.