- Author: Neil McRoberts
Welcome to the thrips population update service for 2014.
General situation Thrips populations seem to have come through the cold dry winter in high numbers and the warm spring is seeing the projected development rates for populations along the length of the Central Valley running ahead of the 30 year average.
Fresno Co The first generation of post-winter thrips probably peaked in mid March. Peak egg hatch for the second generation was predicted approximately a week ago and second generation adults is peaking right now. These early generations of thrips are not a significant threat for spread of TSWV, although some TSWV has already been found around the Huron area and thrips numbers are high. For growers considering an insecticide to reduce thrips/TSWV risk the generations to target are generations 3, 4. Given that TSWV has already been detected and thrips are active, we suggest earlier rather than later action for growers considering insecticide applications. For this part of the Valley, the current forecasts are:
Generation 3 adults projected to peak on May 19th. Control of this generation would require pesticide application in the 2 weeks prior to this date; i.e. in the window from May 5th through 19th.
Generation 4 adults projected to peak on June 12th. Control of this generation would require pesticide application in the 2 weeks prior to this date; i.e. in the window from May 30th through June 12th.
- Author: Neil McRoberts
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.
- Author: Neil McRoberts
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 San Joaquin Valley. In the Fresno area generation 3 adults peaked on May 29th and generation 4 adults will peak around June 18th. TSWV incidence is still low so the the next 10 days to 2 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 are at higher risk from TSWV damage because thrips numbers are already high and the virus is more damaging when plants are infected while still young.
- Author: Neil McRoberts
The temperature has started climbing over the last week and the next seven days will see figures in the mid to high 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 was projected to occur on April 15th and adults from that hatch will reach peak numbers around April 28th. 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.
There is some TSWV in radicchio around the Fresno/Kings Co border but levels are low. Trace levels of TSWV were also reported in lettuce in the Huron area, but these reports have not been confirmed by diagnostic testing and the situation does not appear to have worsened since our last post.
- Author: Neil McRoberts
There are reports of low incidence of TSWV in spring lettuce in the Huron area. We are working with California Leafy Greens Research Board and lettuce growers in the area to assess the situation. The presence of TSWV in another host crop is a risk factor for early movement of TSWV into tomato. For more information about the current situation contact Tom Turini.
The first generation of post-winter adult thrips were expected to peak (i.e. reach maximum size) on March 28th. We are currently projecting that peak egg hatch for generation 2 will occur around April 15th. 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 3 days ahead of 2012 and 2 days ahead of the 30 year average for accumulation of thrips degree days, indicating that thrips activity is more or less typical this season so far.