General situation

Temperatures over the past few weeks have been in the 80s and 90s, ideal conditions for thrips development. The hot weather coming up is also expected to accelerate thrips development and activity. I'm seeing some TSWV infection in nearly every field in Yolo and Solano counties that I visit, though generally at low (<1%) incidence.

Thrips population and outlook

We're in generation 3, with adults predicted to peak in the next week or so and generation 4 adults to peak in early July. Generations 3 and 4 represent the major risk of TSWV getting into crops before fruit set, so if you're planning to use insecticides to knock down thrips numbers, the next month or so is an important period. TSWV is only likely to reduce yields when infection occurs during or before fruit set, so all but very late-planted fields should be far enough along by Generation 5 (predicted to come towards the end of July) to shrug off any new strikes.

General situation

Above-average temperatures this week compensate for below-average temperatures last week, and thrips population projections remain similar to earlier predictions.

Thrips population

Generation 2 adult thrips are peaking now, and will be laying their eggs. Thrips population will be predominantly Gen 3 nymphs through the second half of May. Again--for growers considering treatment, if the field is high risk (in an area that has been heavily affected in the past or you are seeing early infections) spraying in the next few weeks could be beneficial. Otherwise waiting until Gen 4 may pay off in terms of investment in thrips control.

The resistance-breaking TSWV strain from Fresno has been detected in the northern counties since 2021, and last year another resistance-breaking strain was identified and appeared to be the dominant strain in Sutter and Colusa. I'm working with Bob Gilbertson's lab at UC Davis to understand more about the range and severity of these two strains. Feel free to contact me (530-219-5198; palazicki@ucdavis.edu) if you're seeing possible infections and would like confirmation.

Additionally, a reliable immunostrip test is available, which can be performed in the field to verify the presence of TSWV. The cost is $170 for a package of 25 test strips. https://orders.agdia.com/agdia-immunostrip-for-tswv-isk-39300

General situation

Unseasonably cool weather has slowed thrips population projections slightly. However, temperatures may be into the 90s by the end of the week and we expect to see populations continue to develop.

Thrips population

Generation 2 adult thrips are peaking in the coming week. Thrips population will be predominantly nymphs through the second half of May.  I've been seeing a few scattered infections in early-planted fields here in the north. There's a risk that when these Gen 3 nymphs become adults they will be able to spread the virus further. In  historic hotspots, growers considering treatments should think about targeting these Gen 3 nymphs, especially if they are seeing any signs of the virus. Otherwise, generation 4 seems the more likely source for any significant chance for TSWV to spread around, and the more likely to pay off in terms of investment in thrips control.

General situation

Temperatures remain close to historic normals, and are predicted to remain moderate for the next few weeks. Planting is progressing throughout the Sacramento Valley. I've started to see some early TSWV infections in March-planted fields in Yolo County.

Thrips population

We're heading into the second generation of thrips; egg hatch peaked last week, and adults are predicted to peak May 12th (Fig. 1). 3^rd generation adults are predicted to peak in early June, and 4^th generation in early July.

In typical years like this is shaping up to be so far, our normal recommendation is that if you don't know of any local sources of TSWV and crops are not in the ground or are just planted it might be worth delaying any treatment until mid-June. It would allow generation 3 adults to breed and lay eggs, but will catch juveniles developing from generation 3 eggs and suppress the spread of any TSWV that has come into crops with generation 3 adults.  If you do have local sources of TSWV, or if you've planted early and are worried about early entry of TSWV to your crop, consider treatments in weeks 2 or 3 of May to suppress generation 3 thrips, which could be carrying TSWV.

During this important period for thrips management decisions (Generations 2-4), I'll be posting weekly updates to this blog. Please feel free to contact me (palazicki@ucanr.edu, 530-219-5198) if you have any questions.