In 2020, University of Georgia Extension agents measured the levels of tomato spotted wilt virus in 292 peanut fields in 34 Georgia counties.
The survey verified some trends and the use of at-plant treatments for tomato spotted wilt. Mark Abney, UGA Extension peanut entomologist, discussed the survey findings during a UGA Peanut Team production meeting in February. It's a survey, so it has stats and percentages that can veer the mind sideways at times. Abney will give his take on the data after you take a look.
The agents conducted their surveys in August and September. Of the fields surveyed:
- 35% had less than 5% incidences of TSWV present.
- 54% had between 5% and 20% incidences of TSWV present.
- 10% had greater than 20% incidences of TSWV present.
"Growers might say they didn't have a lot of spotted wilt in 2020 and that's good. Thirty-five percent of the fields that were surveyed had less than 5% spotted wilt. It's not a surprise growers had fields with low levels of spotted wilt," he said, but he added that things get concerning in the next category between 5% and 20%, he said.
"If you're down on the lower end of that range, we're probably not too concerned. If a grower is getting up to 15% or 20% of spotted wilt in a field, you're losing yield. You probably want to think about what you can do, whether it's through Peanut RX and managing cultural practices, or changing your at-plant insecticides to get those numbers down."
More concerning is that last category. One in ten fields surveyed had greater than 20% TSWV. That level of TSWV results in tremendous yield losses, he said.
So, what can growers do about it? Last year, growers faced weather-related setbacks and early season issues with seed germination caused by harvest weather on seed peanuts in 2019. But again, he said, growers can still use the Peanut RX tool to assess and reduce their risk to tomato spotted wilt, along with white mold and leaf spot diseases, in 2021.
It's good to remember that TSWV is vectored by thrips. He also said growers who have had too much TSWV for too many seasons may want to focus on something else the survey measured: the number of fields treated with a given insecticide or not treated with one.
Again, take a look at some numbers from the survey, and Abney will give his take after.
Of the 292 fields surveyed:
- 149 were treated with Thimet and had an average of 7% TSWV and 3% of these fields had greater than 20% TSWV
- 82 were treated with imidacloprid and had an average 13% TSWV and 17% of those fields had greater than 20% TSWV.
- 31 were not treated with an insecticide and had an average of 16% TSWV and 26% of those fields had greater than 20% TSWV.
- 11 were treated with orthene and had an average of almost 12% TSWV and 18% of those fields had greater than 20% TSWV.
"As you see with Thimet, when we look at the severe incidence of virus, 3% of the fields treated with Thimet had greater than 20% spotted wilt. Thimet is not perfect at reducing spotted wilt but that's pretty good. You had only 3% chance of getting spotted wilt in 2020," he said.
The second most-used in-furrow insecticide was imidacloprid. "The average virus incidence was almost 13% across the board, but what's probably more important than that is the percent of fields that had more than 20% spotted wilt. So 17%, or almost one in five of the fields treated with imidacloprid had greater than 20% spotted wilt virus. You are losing a noticeable amount of yield in that situation," he said.
Of the fields not treated with insecticide at plant, one in four had spotted wilt greater than 20%. "So if you're in that category where you put nothing at plant or if you think you are in a category you don't want to be in, think about how much spotted wilt you had in 2020 and whether or not you want to try to do something different in 2021 to manage this disease," he said.