- Author: Patricia Lazicki
- Author: Neil McRoberts
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). 3rd generation adults are predicted to peak in early June, and 4th 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.
- Author: Patricia Lazicki
General situation
The colder weather has delayed thrips population development by a few days, but overall the outlook hasn't changed much from last report. The oldest tomatoes have been in ground for more than a month, and planting is progressing rapidly.
Thrips population
Most thrips are currently 1st-generation adults (Fig. 1). These adults are feeding and laying their eggs; second generation egg hatch is predicted to peak in the next 1-2 weeks. Generation 2 adults are predicted to peak in the second week of May.
Figure 1. Predicted thrips population development, based on current temperatures and seasonal long-term averages
For newly hatched thrips to acquire TSWV, the larvae have to feed on an infected plant (Fig. 2). Only thrips that have acquired TSWV as larvae can spread it by feeding as adults. In known hotspots, promptly controlling winter weeds like little mallow (cheeseweed), mustards, and prickly lettuce which may have served as overwinter hosts for TSWV reduces the likelihood of these early thrips generations acquiring the virus and spreading it to young tomato plants.
Figure 2. Thrips life-cycle and relationship to TSWV transmission. Time at each stage is shorter in hotter weather. **The pupal stage, which is in the soil and does not feed, can last much longer in cold weather. Graphic courtesy of Prof. Diane Ullman. Photos by Jack Kelly Clark, UC IPM Program emeritus.
- Author: Patricia Lazicki
General situation
Winter rainfall accumulations and average temperatures in the Sacramento Valley this year are looking similar to the long-term averages. The drying wind and higher temperatures last week mean our first tomatoes are going into the ground this week.
Immediate outlook
Thrips are likely 1st-generation juveniles (1st-gen egg hatch peaked 2/23, and adults are predicted to peak 3/29). Currently 2nd-generation egg hatch and adults are predicted to peak at 4/22 and 5/8, and 3rd generation adults predicted to peak in early June. Thrips control is most effective in the 2nd and 3rd generations.
TSWV isn't transmitted to the eggs, and juveniles must acquire it while feeding on infected plant tissue. Infected adults then transmit the virus to new host plants during feeding. This generation of juveniles can acquire it by feeding on infected host winter weeds, winter crops, or cover crops. Many winter weeds can host the virus, including include prickly lettuce, little mallow (cheeseweed), and sow thistle. Fava bean is a common cover crop plant which can also host the virus. Controlling these weeds can help reduce thrips' ability to acquire and transmit the virus to newly planted tomatoes. This is especially important in old TSWV hotspots.