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 in the next day or so and generation 6 will peak on August 12th.

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 Yolo/Colusa area generation 3 adults are projected to peak today and generation 4 adults will peak around June 27th.  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 and will reduce generation 4 thrips.

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 occur right around now (April 23rd) and adults from that hatch will reach peak numbers around May 6th.  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 thrips generation should be targeted for any insecticides that are planned this year.  Watch this space.

The recent rain front and cooler conditions are likely to have slowed thrips development and kept adult thrips from flying long distances, reducing the chances of spread of any TSWV that might be present.  The first generation of post-winter adults is expected to reach maximum numbers (i.e. "peak") today.  Currently we are projecting that peak egg hatch for the second generation will occur around April 27th.  The weather forecast for the week ahead is for temperatures in the mid to high 70s and no rain so we expect to see thrips activity begin to build. We are 5 days ahead of 2012 and 3 days ahead of the 30-year average for thrips degree day accumulation, indicating that thrips may be active relatively early this year.