Peanut planting is about to get real serious in Georgia, and we are once again monitoring tobacco thrips flight activity for the spring planting season. Producers who have already planted or who are planting this week should be watching peanut fields closely for thrips and signs of thrips injury as seedlings emerge.
We saw thrips numbers increase slightly on our traps from 3 March to 6 April, and we are currently counting thrips collected last week. In previous years, ten or more tobacco thrips per trap represented significant thrips flight activity and high risk for susceptible plants in the field. Our Colquitt County site at the Sunbelt Expo averaged just over 10 thrips per trap two weeks ago.
Current thrips population prediction models suggest that we are currently in a high risk period for thrips. If the predictions are accurate, risk will decline quickly as we approach May planting dates.
Regardless of computer model predictions, we know that the risk of thips feeding injury and Tomato Spotted Wilt is greatest on Georgia peanuts planted prior to 10 May.
Below is a list of the most common thrips management options updated for 2017:
1. Phorate (Thimet 20G) in furrow: Thimet has been around for a long time, and we have years (decades really) of data that show Thimet does a good job of reducing thrips injury. It is the only insecticide that can reduce the incidence of Tomato Spotted Wilt Virus.
Thimet is an organophosphate insecticide, and as with all pesticides, growers should read and follow label instructions carefully. Some phytotoxicity (aka “Thimet burn”) is commonly observed when Thimet is applied to peanut, but this injury has not been associated with lost productivity.
2. Imidacloprid (Admire Pro, Velum Total, various generics) liquid in-furrow: Imidacloprid applied as a liquid in the furrow at planting has given good control of thrips in trials at UGA and other Southeastern universities in recent years. Imidacloprid has been shown to be compatible with most liquid inoculants and fungicides (not all combinations of products have been tested).
Imidacloprid will not reduce the risk of tomato spotted wilt in peanut. Growers should also take careful note of the formulation of the product they plan to use as rates vary by formulation. Applying a 2F product at a 4F product rate will result in significantly less active ingredient than the label recommendation.
Velum Total contains both imidacloprid and an active ingredient targeting nematodes. Growers who want to use imidacloprid for thrips but who do not have a nematode problem do not need to invest in the additional AI, but should choose a stand alone imidacloprid product (e.g. Admire Pro).
3. Acephate (Orthene) foliar spray: Orthene will still kill thrips, and we use it regularly in GA when at-plant insecticides “run out of steam”. The problem associated with leaving off an at-plant application in favor of a foliar spray alone is timing.
This approach requires careful scouting (something that is much less common on our peanut acreage than it should be) and the ability to get into the field on short notice to make an application. Given the hectic schedule of most growers in the spring and the potential for unfavorable weather, being able to cover large acreage with a foliar application is a gamble most growers should avoid.
4. Aldicarb (AgLogic 15G): AgLogic was available commercially on a very limited basis in 2016, but the product performed well in the UGA Peanut Entomology testing program last year. For growers who liked Temik, I expect AgLogic to perform similarly against thrips. We should remember that AgLogic has no effect on Tomato Spotted Wilt.
5. Thiamethoxam (CruiserMaxx Peanut) seed treatment: Thiamethoxam is the active ingredient in CruiserMaxx Peanut seed treatment. Growers should be aware that moderate to severe thrips feeding injury has been observed on thiamethoxam treated peanut when thrips pressure is high.
While we do not currently recommend an automatic foliar insecticide application for thrips on CruiserMaxx Peanut, we highly recommend that growers regularly scout their fields for the presence of adult and immature thrips beginning soon after seedling emergence. The presence of reproducing thips may signal the need for a foliar insecticide application. Thiamethoxam does not reduce the risk of tomato spotted wilt in peanut.
NOTE ABOUT INSECTICIDE RESISTANCE
Thiamethoxam and imidacloprid are in the neonicotinoid class of insecticides. Populations of tobacco thrips with reduced susceptibility to neonicotinoids were documented in 2015. No control failures have been reported in Georgia to date. Resistance monitoring will continue in 2016.
No matter what thrips management tactic is chosen, scouting is still a good idea. Nothing provides 100% control 100% of the time, and the only way to know if a problem is developing is to monitor fields regularly. Price of inputs will be an important factor in decision making in 2017.
We need to be sure not to cut labeled rates in an effort to save money…reduced rates will likely lead to reduced efficacy and can ultimately cost more in supplemental treatments and/or lost productivity.
Another thing to consider is that peanuts planted before 10 May are at an increased risk for tomato spotted wilt virus; none of the insecticides registered for thrips control in peanut will reduce the risk of the disease except Thimet.