It’s that time of year again.  Hay fields, pastures, and home lawns are green and productive.  There could be a problem right around the corner though.  

As summer progresses the subject of fall army worms should be fresh on the minds of livestock producers, hay producers, and homeowners.  These pests can destroy an otherwise healthy stand of bermudagrass in a matter of days.

Fall armyworms prefer well managed bermudagrass, but they can also feed on other forage grasses and agricultural crops including corn, rice, sorghum, and millet. 

The reference for this article is the Mississippi State University publication “Fall Armyworms in Hayfields and Pastures”.

Life Cycle

Fall armyworms cannot survive the winters in Mississippi.  The armyworm is the larval stage of moths that spend the winter months in South America, the Caribbean Islands, and southern Florida.  

 

The timing and severity of fall armyworm infestations can vary from year to year.  Temperature and rainfall have a large impact on population numbers.  Cool/dry years have a negative impact on fall armyworm populations.

The fall armyworm moths are rarely seen, because they travel at night and rest during the day.  The moths are around three fourths of an inch in length.  The moths have gray to dark brown forewings, with white underwings.  They appear to be pale white in flight.

Female fall armyworm moths lay around 1,500 eggs in their two-week lifespan.  The eggs are laid on the grass in white fuzzy masses containing about fifty eggs.  After two to five days, the eggs will hatch.  

The young armyworms begin feeding on the undersides of grass blades.  The top portion of the leaf remains, giving the grass blade a transparent appearance, and making it look like a window pane. This can give the grass a frosted appearance that indicates the early stage of an infestation.  

Fall armyworms consume more grass in the last two days of their fourteen-day lifespan.  This explains why the grass can disappear so quickly.  The armyworm caterpillars then dig into the soil to pupate.  The adult moth will then emerge to complete another cycle.  There can be up to five generations a summer.  Populations increase with each generation.  

Mature fall armyworm caterpillars reach a length of an inch and one half in length. The caterpillars are covered with dark spots and are green or tan in color.   There are four spots at the rear of the caterpillar that form a square.

Control in Hayfields and Pastures

To effectively manage fall armyworms, cattlemen and hay producers must be ready and prepared.  Producers need to check their fields two to three times per week.  When numbers are greater than three caterpillars per square foot, the field should be sprayed. 

Producers should have their equipment prepared, clean and calibrated when fall armyworms appear. Time cannot be wasted repairing spray equipment.  If the caterpillars are allowed to reach the pupa stage, another generation will emerge causing a new wave of destruction.  

Producers should also ensure their private applicator license is up to date in order to use the effective pyrethroid insecticides now on the market.  These insecticides include Mustang Max, Baythroid XL, and Karate. For additional insecticides and application rates see the Mississippi State University Publication 2717, Fall Armyworms in Hayfields and Pastures.  It should be noted that bifenthrin is not labeled to be used on hayfields or pastures.

Control on Home Lawns

Home lawns can be treated with products containing permethrin (38%) (Hi-Yield 38 Plus Turf, Termite & Ornamental Insect Concentrate), bifenthrin (Ortho Bug-B-Gone), or Gamma-cyhalothrin (Triazicide Insect Killer Concentrate).  For a complete list of insecticides and rates refer to page 8 of Mississippi State University Extension Publication 2331 “Control Insect Pests in and around the Home Lawn”.

Small lawns are best treated using a ready-to-use product that attaches to the end of a garden hose.  Treatment of large lawns requires using spray equipment that employs the use of a lawnmower, ATV or tractor. Often the most convenient and easiest way to treat large lawns is to hire a licensed commercial applicator.

Use the above information and techniques to be prepared to defend your lawn, pasture, or hayfield from a possible fall armyworm invasion.

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