Understanding the movement and spread of thrips is a giant step in managing both insect damage and reducing risk from tomato spotted will virus (TSWV) that is vectored by these tiny insects.
Peanut tests in Virginia indicate thrips damage is not related to variety, though tomato spotted wilt virus that is vectored by thrips is directly related to variety differences. The combination of variety selection and more effective management of thrips will significantly reduce the risk in peanut production.
Speaking at the recent Virginia Peanut Growers Association annual meeting, Virginia Tech Entomologist Ames Herbert said thrips infect peanut fields from a single flight, which he contends is good news. “If we can use weather patterns and other input data to determine when a thrips flight is most likely to occur, we can do a better job of managing these pests, he explains.
Thrips feed inside developing flower buds and in newly expanding leaves of plants. Their feeding damage is not seen until deformed flowers and leaves expand, leaving peanuts unmarketable. These tiny insect pests have a wide range of hosts, including many ornamentals and most native shrubs and grasses.
Though thrips are not influenced by peanut variety, tomato spotted wilt virus damage is significantly different among varieties. By doing a better job of managing thrips and planting varieties that are less susceptible to TSWV, growers can greatly reduce damage from both the insect and the virus.
Growers have some reliable tools to manage thrips and these will be more effective when more precisely timed. Herbert says it's hard to beat the proven combination of Temik or Thimet in-furrow, followed by a foliar application of Orthene.
A new product being developed by Bayer is an in-furrow application that is a combination of aldicarb and imidachloprid will be a good option for growers, if it is granted a full use label. Though still in development, this new product has performed well in both cotton and peanut tests, Herbert says. He explains that the future of this new product is directly tied to re-registration of aldicarb.
Thimet in-furrow followed by Orthene performed well, but there was some yield drag. Herbert explains there was a lack of virus in some of the test fields, which has been linked to increased plant damage when using Thimet.
Leaving off the in-furrow treatments and using two foliar applications did not provide control comparable to either Thimet or Temik used in-furrow, plus one application of Orthene.
Though there appears to be little difference in thrips levels or plant damage between in-furrow plus Orthene versus two foliar applications of Orthene, the big difference shows up in yield, Herbert says.
“It is important from an economic standpoint that growers understand either Thimet or Temik will give good thrips control, but only for 20 days or so. After that thrips populations begin to build and a foliar application is needed. However, Herbert stresses, in his tests there was no yield advantage from using more than one foliar application in combination with either Temik or Thimet.
In addition to the standard treatments, Virginia researchers tested a new pyrethroid that is in development and is similar to Karate. They also looked at Baythroid, another pyrethroid, but neither provided the level of control, nor final yield advantages of the standard in-furrow plus one foliar application.
The top performer in the thrips insecticide test, Herbert points out, was the experimental compound being developed by Bayer.
There was no correlation between variety and thrips damage — insect damage was equally spread among all the varieties in the test. There was a huge difference in thrips damage between treated and untreated, from nearly zero on treated plots to six on the damage scale, which is high, Herbert explains.
“As expected we saw less virus in plants treated with insecticide. We also saw a yield increase of over 1,000 pounds per acre with Temik or Thimet, compared to untreated plots. By adding one foliar application of Orthene, researchers saw an additional 256 pounds per acre increase,” Herbert says.
TSWV damage was significantly less in Georgia Green and other runner type varieties than with the Virginia type varieties. Georgia Green was the overall highest yielding variety in the test. Among the Virginia type varieties tested, Brantley, and Gregory had more damage than Wilson, which was the highest yielding Virginia type in the test.
Across all varieties, insecticides increased yields by 816 pounds per acre. Though different insecticides produced different yield increases, Herbert stresses the main point is to use something to control thrips, especially in fields with a history of TSWV.