Armyworms have invaded Cole County, according to lawn care specialists.
The University of Missouri Agriculture Extension Office has reported cases of armyworms in and around Morgan and Moniteau counties. These pesky creatures can easily devour a lawn in a short amount of time and are great annoyances to forage farmers of fescue or alfalfa grasses. They have also been known to feast on soybeans. Their population usually peaks around late summer and fall, according to a press release from the extension office.
"These are not new to Jefferson City," said Dan Schmitz, state licensee applicator with Ground Control Lawn Spraying Inc. "They came through en mass probably 10 years ago. They have been here before, and it has been a while, and people have forgotten about it. So people need to check their lawns."
Schmitz said of the 30 yards he has looked at in the last day around Cole County, 20 were infected with the worms. Also, many who had left town for the holiday weekend had green lawns when they left but brown dead ones when they returned, he said.
"If they lost their lawn from the worms, nine times out of 10 the grass will rejuvenate itself, because the worms don't eat the root system," Schmitz said.
The larvae are active in the early and later parts of the day, so scouting for them is best around these times. Three or more larvae per square foot indicates an infestation, according to the extension office. Schmitz said some of the yards had 10 times that amount per square foot. Another good indicator is a bunch of dead grass and a lot of birds, he said.
Pseuduletia unipuncta, or the true armyworm, requires 41 to 66 days to go from egg to adult worm. True armyworm larvae have two characteristics that distinguish them from other armyworm larvae: white-bordered with an orange line down each side of the body and a large, single dark spot at the base of each abdominal proleg. The proleg is the stub structure found on the ventral surface of the abdomen of most larval forms of insects.
There are also Yellowstripped armyworms, spodoptera ornithogalli. The larvae of which can be distinguished from other armyworm species by their paired, black, triangular spots along the back of each abdominal segment and a thin yellow line running lengthwise through each row of spots.
Then there is the fall armyworm, spodoptera frugiperda. These worms have no black spots on their prolegs and a inverted Y on their head. Finally, there is also the beet army worm, spodoptera exigua, which has green to black coloration with a dark head and black spots on the sides of the abdominal segments behind the head.
Pyrethroid insecticides are effective in controlling armyworm outbreaks. Two products recommended by the extension office for fall armyworms in pastures are zeta-cypermethrin (Mustang Max) and lambda-cyhalothrin (Warrior II). Control is achieved if 20 (or more) gallons of water is applied per acre.
For more information on armyworms, contact the local extension center and ask for MU guide 7115: "Managing armyworm complex in Missouri field crops."