2009-10-29

Armyworms marching toward Bandera County?

Contributed

The recent rains throughout the region have brought on “armyworm” problems in “Bermudagrass” hay fields or pastures, fall-planted grain sorghum, sorghum Sudan, sweet corn or oats.

Recently planted grass crops or highly managed hay and pastures will be especially attractive to fall armyworm moths for egg-laying. Before the eggs hatch, heavy numbers of the larval insects can devastate hayfields and pastures due to their insatiable appetite for green grass. Grass crops can be seriously damaged or completely stripped of green leaf tissue.

“To date, there are no known cases of Armyworms in Bandera County, but they are all around us,” reported Warren Thigpen, County Extension Agent in Bandera for Texas AgriLife Extension Service.

Producers in the region are urged to scout their pastures, hayfields and recently planted grain crops for “armyworms” because any green grass crop may be at risk at this time.
Unlike fall armyworms that feed around the clock and will be up on the plants throughout the day, true armyworms feed primarily at night and will not be found up on plants during the day. During the day, producers should look for true armyworms in the crowns of plants and under debris on the soil surface.

Tips for locating armyworms include:
• Any green grass crop is currently at risk for “armyworm” damage and should be scouted.

• Large numbers of birds congregating in fields may be feeding on the caterpillars.

• Low areas in a field are particularly susceptible to infestation.

• Small, clear areas – referred to as “windowpaning” – on leaf blades are an indication that larvae have stripped away one surface of the green leaf tissue. This occurs because the mouthparts of a caterpillar are too small to bite all the way through the leaf.

• Small or elongated holes in leaf tissue can indicate larval presence.

• If clear areas or small or elongated holes in leaves are observed, “armyworm” larvae may be present on plant stems, leaf blades or in the crowns of the grass plants and under debris on the soil surface.

Producers should scout several representative areas of a field. A good scouting tool to use is a sampling ring that encompasses an area equal to one square foot. A very durable sampling ring is easy to make using a 42 _-inch length of shielded cable or other flexible cable. Abut the two ends of the cable to form a circle and secure them in that position using a short length of copper tubing of a diameter comparable to the cable.

The threshold for fall armyworms is three larvae, per square foot.

There are several ways to manage these “armyworms.” When “armyworms” are found in a hayfield, it may be possible to mow and let it dry down. Alternatively, the producer could turn livestock into an affected field so they can eat the grass before the armyworms consume it. These methods require close monitoring to ensure any surviving larvae don’t prevent grass from growing back.

Prevention of regrowth is more likely to occur if the larvae are predominately half-grown.

Chemical control can be very effective and recommended labeled products for armyworms typically have malathion, carbaryl, methomyl, or pyrethroids as active ingredients.

Contact the Bandera County office of Texas AgriLife Extension Service at 830-796-7755, if you need more information or have questions.