A Trifling Place
9:41 am
Mon February 18, 2013

A Trifling Place, Episode 6: When Cankerworms Attack

Welcome to "A Trifling Place," a podcast dedicated to exploring the ins-and-outs of Charlotte.  

In our last episode (Charlotte's Tree Obsession), we ended with this sound bite: "Die, cankerworm, die!" 

That's city arborist Donald McSween back in 2008 when WFAE's Lisa Miller followed him on his war against the cankerworms.

He also had some help: citizen soldiers like Sophia Hollingsworth. 

"We picked them off and didn’t feel bad at all about mooshing them because we felt it was one less cankerworm," Hollingsworth says. "And I don’t feel bad about any of them dying. It’s the canopy that Charlotte is known for and the trees are more important than the caterpillars. Hate the green monster."

Five years later, the fight against the inch-long creatures continues.

Credit Tasnim Shamma

In fact, they're often called inchworms. They're light to dark green in color and they're moths, but the females don't grow wings. In the spring, female cankerworms emerge from a cocoon in the ground and climb the trees as high as they can – usually about 90 feet – to lay their eggs.

Entomologists don't know why, but a parasitic wasp that usually controls the cankerworm population has not been reproducing well in Charlotte for the last 25 years. The wasps lay their eggs in the cankerworms eggs, killing them off.

"The population went up and it never would go down," McSween says. "So the population was very high every spring. We had thousands, millions of caterpillars eating all the foliage of our trees. That can be a nuisance but the major thing was repeated defoliation of these large old trees, threatens their health."

McSween explains that trees store their food to get through the winter and use their energy to grow new leaves. When the cankerworms eat through all the leaves multiple times a year, large old willow oaks are especially prone to death.

Weapon #1: Insecticide

So McSween had to come up with a battle plan. There are two weapons he uses in combat. The first and most expensive is insecticide.

(Note: The city uses an organic insecticide called Bacillus Thuringiensis that kills only leaf-feeding caterpillars. It lasts 48 hours from the time it's sprayed.) 

The first time the city did an aerial spray was in 1992. Back then, the spray included the Cherry, Eastover and Myers Park neighborhoods. In 1998, the aerial spray spread to about 20 different communities. The most recent spray was five years ago in 2008. 

It went all the way from South Boulevard up to the University area and covered about 40 percent of the city. It required federal and state approval, six planes, one and a half million dollars and a year's worth of preparation. "The spray really worked well. We're hoping people won't become complacent and will keep up with the banding program to try to keep the population down to hopefully prolong the period of time where we would have to do another aerial spray."

Weapon #2: Tanglefoot

The banding program includes a sticky glue called Tanglefoot. It's a glue that traps cankerworms on the black tar paper that hug the trunks of many trees in Charlotte. The city bands about 5,000 Willow Oaks each year.

But there are still some cankerworms outside his office in west Charlotte.

"There you see 'em. Those are all females," McSween says. "They came out of the ground, climbed up the tree. They were going to lay their eggs at the very top and the trap caught 'em. And then the moths with wings are males. And what happened is the female puts out a pheromone, which is a perfume. And you ladies thought you were the first to have perfumes. But these attract the male and of course they get caught in the trap too. Each one of these females can lay 100 eggs. So you're looking at probably, oh … 1,000 females on there.

"In behind that is a batting material, kind of like cotton or insulation. And it keeps ... if the female gets under the trap, it'll stop her. And this is tar paper and then you have the Tanglefoot which is a sticky material which stays sticky all the time, even in cold rainy weather."

The black tar paper and Tanglefoot to band your tree can cost $15-20. The city relies on residents to band the majority of the trees and even distributes grants to communities with major cankerworm infestations. The Plaza Midwood neighborhood actually has a little fun with it.

Since 2006, it's hosted an annual festival called the Fall Crawl where people band their trees together. There's a costume parade, live music, food and games for kids. If residents don't band their trees, cankerworms can easily migrate to other trees because they're so light and can be blown from one tree to another. So the city promotes neighborhoods banding together. And if you're the only house on the block without a black band around your tree?

Perhaps your neighbors are cursing you under their breath for infecting their trees.

"In some neighborhoods, in the past, prior to the aerial spray, we had between 3 and 4,000 females caught on an individual tree," McSween says. "So in those cases sometimes there were so many of them they were overwhelming the bands and of course then you'd have some that could walk across the dead bodies of their sisters and get up in the tree. Good subject isn't it? Just think about that while you're asleep."

Umm … Sweet Dreams?