They’re tiny, they’re hungry, and they’re coming for your lawn.
Autumn army worms have decimated at least 40 lawns in Burlington since late August, when army moth eggs began to hatch and a voracious army of inch or two inches long caterpillars was unleashed.
“They’re called army worms because they’re known to come in flocks and take away entire pastures, so it’s like a small army of marching caterpillars,” said Morgan Hoenig, local food coordinator and master gardener for the Iowa state’s Des Moines County office University Extension and Outreach.
Army worms are usually a problem in southern states like Florida, but after a fertile breeding season, the moths that produce them have fanned out and ride storm winds and the jet stream into the Midwest.
“This is widespread damage across the country,” said Adam Thoms, a turf enhancement specialist for the state of Iowa, explaining that they were seen from Georgia and Alabama to Ohio and Indiana and Iowa. “In the Burlington area in particular, we believe there was alleged damage from the army worm.
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While the caterpillars are yet to be spotted even in Burlington or anywhere else in the state, there have been numerous sightings of army moths and eggs that resemble small, clumped styrofoam balls that are placed on everything from house walls to flags, according to Thoms.
“The moth lays eggs everywhere it lands and they really have a wide range of food sources,” Thoms said.
Thoms first received a report on suspected army worm damage from Burlington on August 29. Images he received show a once lush garden that has turned brown. The caterpillars, said Thoms, also damaged a neighboring alfalfa field.
“They stay in one area until they run out of food and then they move to the next area and eat that,” Thoms said, explaining that the caterpillars have decimated entire golf courses in states like Florida and Texas.
Thoms suggested that the damage seen so far in Iowa may only be the tip of the iceberg.
“For this to really happen, as with any pest, the population has to be built up in such a way that it is harmful, so we could be at the forefront of the population and it is just not enough to have that damage yet,” said Thoms.
Which vegetation is at risk?
Army worms like some grasses more than others, which is why Matt Hall believes Burlington Golf Club’s lawn has not suffered any damage.
Hall, the golf club’s superintendent, said he had noticed masses of eggs and moths all over the course.
“They’re pretty much everywhere,” Hall said, noting that he had seen the eggs on flagpoles and tee markers, but had not yet seen any signs of damage. “The planes, tees and fairways are all made of bentgrass.”
What armyworms like is perennial ryegrass and blue grass.
“Unfortunately, most Iowa yards are made up of perennial ryegrass and blue grass,” Thoms said.
The caterpillars are also known to feed on alfalfa and hay fields, including one in Lee County.
“There was a hayfield or a pasture field that was completely eaten up,” said Hoenig.
They have also been found in corn fields, but they do not eat corn kernels, and the Iowa corn fields are now mature enough that serious damage from army worms is unlikely.
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What can you do to prevent armyworms?
Hoenig said the easiest way to keep armyworms from entering your lawn is to keep a vigilant lookout for the egg masses. If one is found on your property, you can just throw it in the trash.
Thoms said the eggs can be easily wiped off with soap and water.
Hoenig cautioned against treating the lawn with insecticides as this would harm the beneficial insects in your garden.
Army worms have also been shown to be tolerant of some insecticides, although Thoms noted that it is unclear what insecticides these could be as he does not know that they are used against Army worms in Iowa.
“There are certain classes of insecticides that they were likely exposed to in the south, and that is the pyrethroids, so chances are these won’t work as well,” Thoms said.
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The armyworms and army moths that do not devastate lawns or fields will not survive the first frost, so it is only a matter of time before they die.
“That’s a lot of pests in the warm season,” said Thoms. “You’re not going to hibernate here. You have a hard time hibernating in North Florida.”
How can you help your garden recover from an army worm invasion?
The summer rains helped ensure that the lawn did not sustain irreversible army worm damage, and water is key to the lawn’s recovery.
“When (army worms) expose the crown of these more grassy plants, the crown can dry out and die,” Hoenig said.
She and Thoms said that watering the lawn frequently after an army worm invasion can help the grass recover fully in the spring. Thoms said using fall manure and overseeding brown spots might also be required.
“Water your garden and fertilize it,” said Thoms. “That will help him recover.