Harvest is now well underway and despite high numbers of thrips TSWV incidence remains low across the region.  Only late-planted crops are now at risk from serious yield loss from TSWV. Yield loss is worst when plants are infected before fruit set.  If any crops are still pre-set they should be considered as priorities when considering insecticide application over the next couple of weeks.  Generation 5 of the thrips is expected to reach peak hatch on July 27th and generation 6 will peak on August 17th.

Temperatures are predicted to peak at 100+ F at the end of this week before returning to the high 80s F early next week.  Thrips will develop rapidly under these conditions.

Thrips numbers are now high throughout the southern Sacramento Valley and San Joaquin Valley.  In the eastern half of San Joaquin Co. generation 3 adults are projected to peak on June 10th and generation 4 adults will peak around July 3rd.  TSWV incidence is still low so the the next 3 weeks are an ideal period for insecticide application if you are considering treatment for thrips/TSWV.   Spraying at this time will reduce egg laying by generation 3 to some extent and will reduce generation 4 thrips numbers.

Recently planted crops will be most at risk from spread of TSWV because the impact of the disease is greater the younger the plants are at the time of infection.   

The temperature has started climbing over the last week and the next seven days will see figures in the high 70's to mid 80's F.  This is the ideal range for thrips development so we can expect the current (second) generation to develop right on schedule.  Peak egg hatch is projected to on April 27th and adults from that hatch will reach peak numbers around May 11th.  These thrips are the first generation which will have had a chance to grow on tomato as juveniles this year, so with very low levels of virus around, there is only a small risk of any immediate spread of TSWV.  Depending on how much TSWV we see in crops over the next few weeks we'll be able to give an indication of which generation should be targeted for any insecticides that are planned this year.  Watch this space. 

The first generation of post-winter adult thrips were expected to peak (i.e. reach maximum size) on April 7th.  We are currently projecting that peak egg hatch for generation 2 will occur around April 28th.  Generation 2 juveniles from that egg hatch will be the first opportunity for thrips feeding on tomato to acquire TSWV if there is any present.  Given the very low levels of TSWV in planting material the risk of this happening is likely to be low.  The recent period of unsettled weather will give way to more stable, warmer conditions next week with temperatures in the mid to high 70s.  We can expect thrips activity to start to increase under these conditions.  At this point in the season we are 1 day ahead of  the 30 year average for accumulation of thrips degree days. This suggests that thrips activity is more or less normal for this time in the year and there is no elevated risk for spread of TSWV at this time.