Iowa bracing for latest tree pest: the gypsy moth

Iowa will use pheromones to control a skyrocketing population of gypsy moths that threaten the state's oaks and other trees.

Tivon Feeley, forest health specialist with the Iowa Department of Natural Resources, said just 82 adult male gypsy moths were captured in Iowa in 2009. That number jumped to 2,260 last year.

The moths, which have few natural predators, had been found in small numbers since 1972, when monitoring began.

“Last year it was a huge increase,” Feeley said. “It looks like they're getting established in the state of Iowa.”

Unlike the emerald ash borer, which was detected in Iowa last year and decimates ash trees, the gypsy moth feeds on 300 types of trees, including spruce, though their favorite is oak, Iowa's state tree.

Imported to Boston in 1869 as an experiment to provide silk for the textile industry, gypsy moths have become the major cause of hardwood tree defoliation in the Eastern United States.

Feeley said pheromone flakes will be used in June in Winneshiek, Jackson and Allamakee counties in northeastern Iowa, where the majority of moths have been trapped.

The scent overwhelms adult male moths into not finding a female during the mating season. 

“Hopefully, we can stay on top of it in Iowa,” Feeley said.

The pheromones are safe and only target gypsy moths, he noted.

Foresters with the Iowa DNR will work with the Iowa Department of Agriculture and Land Stewardship, APHIS-PPQ, the U. S. Forest Service and the USDA Gypsy Moth Slow the Spread Foundation.

The foundation is funding the pheromone treatment, which costs $7 per acre. Feeley said the goal is to treat 73,000 acres.

Feeley said especially in Jackson County, the moths appear to be spreading naturally, as opposed to being brought in to the state on boats, campers and other places where the moths lay their eggs.

Northeastern Iowa was also the site where state officials confirmed an ash borer infestation in May, along the Mississippi River in Allamakee County. 

Damage from gypsy moths is most noticeable from May through July, when the caterpillars defoliate trees, but the caterpillars also crawl over homes, RVs in campgrounds, vehicles, outdoor furniture and lawns, leaving waste from their feeding. Hairs on gypsy moth larvae can also cause allergic reactions, resulting in rashes on the inside of legs and arms and the stomach.

Losing leaves early in the growing season stunts the tree's health and inhibits oaks from growing acorns. Repeated defoliation can allow other diseases, pests or drought to kill the tree.

“It is a concern for all Iowans,” said Patty Petersen, field coordinator for Marion-based Trees Forever. “We learned we can't eradicate it, but at least we can slow the spread.”

Petersen said homeowners can monitor their trees for defoliation and ask their county extension office to identify caterpillars.

Topical treatment, especially of mature oak trees, is impractical because few homeowners have sprayers that could reach the treetops, she said.

Both the hunting and wood industry would be adversely affected by gypsy moth damage.

Acorns are an important food source for deer and turkey.  The DNR notes that hunters spend hundreds of millions of dollars each year pursuing Iowa whitetails and gobblers.  Sawmills and timber buyers buy oak trees for the popular wood.  The wood industry supports 18,000 jobs in Iowa with an annual economic benefit of nearly $1 billion. 

Forest ecosystems suffer from the loss of shade the leaves would have offered as protection for birds and their offspring. More light reaches the forest floor, leaving invasive plants to grow and spread faster.  

According to the DNR, of the 26 million trees that line city streets in Iowa, 5.5 million are preferred host trees for the gypsy moth. That would cost nearly $3 billion to remove if they died as a result of not controlling the moth.