For the second summer in a row, a high number of small green-and-black inchworms called cankerworms have made Bismarck trees their homes and fed on their leaves.
Though these worms are not considered a "major threat," according to the city forester, in recent weeks they've wreaked havoc on trees along the Missouri River bottom, including at Mike Beck's farm off River Road.
About a week ago, Beck started to notice the green on his trees diminishing.
"Within two days it looked like a hail storm hit the trees," he said.
Days later, Beck said, it was like "living in a sea of worms." He couldn't mow his grass without being covered in worms, which he said "decimated" his apple trees.
"I've seen (the worms) in years past, but nothing like this," he said.
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Bismarck City Forester Doug Wiles said the worms come in cycles, not every year, and that populations began increasing last summer.
"It's not so much in town. It's in the native woodlands in those neighborhoods close to the river bottom where we're seeing the most damage," Wiles said.
The worms mainly attack hardwood trees, including basswood, bur oak, green ash and maple, but they'll feed on the leaves of other types of trees as well, according to Beth Burdolski, a North Dakota State University Extension Service agent for agriculture and natural resources in Burleigh County.Â
Burdolski said the worms can feed on the leaves for about three to four weeks before leaving the trees via a silken thread and burrowing in the soil. They emerge in the fall as moths.
Even if a tree is completely defoliated, a healthy tree should re-leaf in about a couple of weeks after the worms have stopped feeding, she said.
In the past, when the worms were at their worst, Bismarck did aerial spraying to protect the trees, with the last time around 2007, Wiles said. But the worms have not reached that point yet this year.
"If I were to observe that happening in the city for a couple years, then we would look at proposing something to (the city commission) about doing some aerial spraying," he said.
For now, residents are advised to water trees affected by cankerworms to help them restart the process of growing back their leaves.
Insecticidal treatments are effective when applied at the right time, usually in late spring or early summer prior to the worms feeding, according to Burdolski. Banding trees using a stick substance called Tanglefoot also can prevent cankerworms from reaching elevated levels.
Beck said he applied a pesticide to his apple trees, but now all he can do is wait.
"The trees are actually coming back. I see the faint, green," he said. "Four or five days ago there was just nothing left."