Army worms invade after summer rains

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The recent showers have brought out an increase in the army worm population. This seemingly small insect can do big damage to crops and hay fields overnight when conditions are right. The army worm is actually a caterpillar that hatches from the egg of a small grayish brown moth. They feed heavily on new growth which usually follows a good rain.

Armyworms in our area are most commonly found to affect Bermuda varieties, especially those that have been fertilized and are lush and green. However they will feed on other grass types as well. Most of their feeding is done at night when it is cooler. During the day they will take shelter from the heat low in the foliage or in the top layer of the soil. It is a good idea this time of year to frequently check for the caterpillars as they can destroy crops and forage rather quickly.

After hatching if not treated the caterpillars will feed for two to four weeks depending on temperature. However 85 percent of the food consumption happens in the last 4 days of development. When checking for the caterpillars walking the yard or pasture early in the morning, when the dew is still on the grass, in rubber boots can usually give you an idea of their presence because you will see them on your boot. When deciding if the numbers are high enough to justify the application of an insecticide you should mark a square foot and count how many caterpillars are present in that single square foot. The treatment threshold is 5 or more caterpillars found within 1 square foot.

There are several treatment options when dealing with Armyworms. The some common active ingredients are, Carbaryl (Sevin), S-Cyano (Mustang Max), 57% Malathion, cyfluthrin, and lambda cyhalothrin. Other name brands include Tombstone, Warrior II, Prevathon, Intrepid and more.

Always follow the label instructions when using chemicals.  Read and carefully consider the restrictions on the target crop before applying the chemical. There is often a waiting period on each chemical for harvesting crops, grazing, or hay harvesting. It is also recommended to treat in the cooler parts of the day, morning or late evening, to reduce chemical loss and deterioration.

For more information on this subject call the Texas A&M AgriLife Extension Office at 936-348-2234.

Chadd Caperton is the agricultural extension agent for Madison County. 

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