Monday, July 30, 2018

Fall Army Worms

Hay producers and cattlemen should be alert for fall armyworms for the remainder of the growing season. Fall armyworms are the most damaging insect pests of bermudagrass hayfields, and undetected infestations can eat a lot of grass in a surprisingly short time. A hay field that looks beautiful and almost ready to cut on Thursday morning may be nothing but stems by Saturday. As the name implies, populations are highest in the fall, but damaging infestations often begin occurring in July. This insect does not
overwinter in the state, but moths migrating from more southern regions return each year to produce several generations, with numbers increasing each generation. Some fall armyworms are present every year, especially in southern Mississippi, but heavy outbreaks sporadically occur, reaching damaging numbers earlier in the year and/or farther north and resulting in the need for more insecticide treatments throughout the state. Fall armyworms will also damage bermudagrass in sports fields and home lawns.

Control: Fall armyworms are easily controlled with timely insecticide sprays, but you have to detect infestations early and have your spray equipment ready to go. For hayfields, treatment is recommended when counts exceed three caterpillars per square foot (only count caterpillars that are ½ inch long or longer). Mature caterpillars are about 1 ¼ inches long and vary in color, from light green to beige to almost black.


Key Points for Fall Armyworm Control in Hayfields

  • Check fields two to three times per week
  • Check your sprayer and have it prepped and ready to go!
  • Treatment is recommended when populations exceed 3 caterpillars per square foot
  • Only count caterpillars that are 1/4 inch or longer
  • This is a very conservative/aggressively protective threshold, some states say 3 to 5, or more.
  • But, right now at least, hay is expensive and insecticides are cheap.
  • Medium range rates of pyrethroid insecticides work well on fall armyworms
  • Mustang Max at 1 gallon to 40 acres, or Karate Z at 1 gallon to 80 acres, are examples
  • Many dealers sell generic pyrethroids—be sure they are labeled for pastures
  • Bifenthrin is not labeled for use on hayfields or pastures!.
  • Pyrethroids are restricted use products—buyers need a current private applicator card.
  • Adding a growth regulator (Dimilin or Intrepid) to the pyrethroid will increase residual control
  • Under heavy pressure it is not unrealistic to have to spray a cutting two, even three times
  • Keep on checking!
Submitted by: Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service