Insect Guidebook
2017 Insecticide Updates Defoliation yanava Majumdar, Alabama Extension entomologist, has been updating growers on the status of several newer insecticide products. He has developed a peanut IPM slide chart as a handy tool for producers and crop advisors to quickly find pest scouting practices and management options. Always read the insecticide label before use as recommendations may change. n Imidacloprid is the active ingredient in Sherpa and Velum Total (neonicotinoid insecticides). Majumdar says imidacloprid is very good in early season applications to protect against small insects such as thrips. Thrips later in the season can be controlled with foliar insecticides such as spinetoram and acephate. n Besiege is a broad spectrum premix insecticide with a synthetic pyrethroid (Group 3, similar to Karate) and chlorantraniliprole (Group 28, similar to Prevathon registered in peanuts). Prevathon and Besiege attack the nervous system of insects in a different way than pyrethroids. Coragen rapidly stops insect feeding but kills the insects in one to three days. Coragen is primarily a stomach poison with long residual and translaminar action, meaning the product can move into the leaf tissue for greater effectiveness against pests. n Xentari is a Bacillus thuringiensis (Bt) or natural selective insecticide that can be used in situations where there is insecticide resistance. As a Bt product, Xentari is biorational with short residual and stomach action, according to Majumdar. Bt acts only on caterpillars and is not likely to harm natural enemies. Bt insecticides can be tank-mixed with other products, and are ideal for use as preventive sprays where insect pest pressure is low. Xentari is a Bt product that is very effective on some tough-to-kill caterpillars such as armyworms, but needs to be sprayed every week to prevent caterpillar outbreaks. n Radiant is a good material for thrips control in pre-bloom peanuts, according to Majumdar. He notes that it will not control thrips located inside peanut flowers. Radiant provides quick knockdown of thrips populations, and offers residual control for 10-14 days. n Belt insecticide was an excellent control for caterpillar pests, but Majumdar says manufacturer Bayer has cancelled its registration due to EPA regulations. Belt is a selective insecticide just like Bt and has a very good residual with translaminar action. Majumdar says growers can use existing supplies of Belt until these supplies are depleted. It is a good idea to contact your pesticide dealer or company representative for any sudden change in regulations with existing stocks. n Intrepid Edge is another new premix insecticide with spinetoram (similar to Radiant) and methoxyfenozide (insect growth regulator). Majumdar says the insecticides Diamond or Dimilin will also target caterpillar pests, and either can be used to help space out applications of pyrethroids during hot summers. Growth regulator insecticides belonging to groups 15 and 18 are very useful for late-season caterpillar outbreaks during drought conditions when there is a strong chance of getting spider mites. He adds that growers should not overuse any one insecticide to reduce insecticide resistance. Overall, Majumdar suggests that the pesticide industry is moving toward more selective and long residual products that can reduce the number of applications and increase grower profits. Research in Alabama and Georgia is continuing to look at major pests like burrower bugs, spider mites, and caterpillars supported by grants from the National Peanut Board and producer associations. t
A
BY JOHN LEIDNER
risks Chad Abbott, a Mississippi State University graduate student, has completed a study that shows what can happen when insects defoliate peanut plants. His research assessed the impact of defoliation or leaf loss at various times during the growing season and how this leaf loss impacted yields. In these tests, peanuts were defoliated at 35, 50, 65, 80, 95 and 110 days after emergence. The goal of his research is to come up with thresholds that growers and consultants can use in deciding to use insecticides to kill defoliating pests. He says insect treatment thresholds now in use may be outdated. “The defoliation in our tests simulates the insect defoliation we see from the green cloverworm, corn earworm and armyworms,” Abbott says. He found that the time of the defoliation makes a big difference in how peanut plants can respond. “If peanuts are defoliated early in the growing season, they can compensate,” Abbott says. “But if the defoliation occurs at 11 to 12 weeks after emergence, that’s when we see yield loss.” Abbott says peanuts are most vulnerable to defoliation during peak pod filling, about 80 days after emergence. “We found that 10 to 20 percent defoliation during this time resulted in significant yield loss,” Abbott says. “A 10 percent yield loss would warrant spending $19 to $22 per acre for a Prevathon insecticide treatment.” Mississippi State University entomologist Jeff Gore says, “No grower would allow 100 percent defoliation, but in this study we wanted to see when defoliation is damaging.” Gore said Abbott’s study showed more yield loss with defoliation at 80 days after emergence than at 40 days after emergence. The studies suggested that at 40 days after emergence, each 1 percent defoliation would lose 4.15 pounds per acre, while at 80 days after emergence, 1 percent defoliation would lose 13.6 pounds per acre. “You can lose 136 pounds of peanuts per acre with 10 percent defoliation at 80 days after planting,” Gore says. t BY JOHN LEIDNER
April 2017 Southeastern Peanut Farmer
21