General outlook & thrips population
Planting will be wrapping up over the next couple of weeks, though the heat wave coming up next week may cause delays. In general, it’s been good spring weather and earlier plantings are progressing well.
The warm weather in the forecast has pushed up population predictions by a few days from last update. We’re currently at the peak of generation 2. These adults are feeding and laying their eggs. The 3rd generation juveniles that hatch will need to acquire TSWV by feeding on infected plants before they are able to transmit it as adults. Generation three adults are predicted to peak in the first week of June.
For fields in areas which have had high TSWV pressure in the past the 3rd generation can be a strategic time to spray,especially if you are seeing infected plants. In general, the 3rd and 4th generations are considered to be a good target for sprays to processing tomato, as earlier generations of thrips are less likely to carry the virus and later generations are less likely to cause yield loss.
Thrips and TSWV monitoring
The first TSWV infections have started to show up on pepper and tomatoes in the south Sacramento Valley. However, incidence is still very low in the fields I have walked. Yellow sticky cards placed in historic hot spots show a relatively high thrips pressure, and we’ve heard from others who are monitoring that they’re seeing the same. As the weather warms up, it will be interesting to see where things go.
Field scouting
Symptoms of TSWV in tomato vary considerably depending on the variety. The plant on the left shows a typical symptom of bronzing and necrosis on the young leaves. The plant on the right has very marked leaf yellowing and necrosis. Foliar symptoms of TSWV on tomato almost always include some necrosis and where only part of the plant is affected, it will be on younger rather than older leaves.
Young pepper plant with TSWV. This field was at early fruit set. Note the combination of mottling, chlorosis and necrosis, tending to affect the younger leaves
Alfalfa mosaic virus, in the same pepper field. The chlorosis is more marked, and there is relatively little necrosis.
AgDia produces a reliable immunostrip test for TSWV that can be performed in the field: https://orders.agdia.com/agdia-immunostrip-for-tswv-isk-39300 . These are very helpful given TSWV’s wide range of symptoms and the fact that there are many lookalike diseases. Or feel free to contact me (Patricia; 530-219-5198) if you have a suspected infection you would like to confirm.