In case the heavy rains high humidity have kept you inside most of the summer, you just might now be noticing that Woodbury (and most of the metro) has been invaded by Japanese beetles.
Woodbury resident Lisa Thor first noticed the beetles in August last year. Thor, who lives in the city’s Highland Heights neighborhood, said this year she noticed the bugs when she put out her flowering annuals.
“I think I was finally able to get my annuals out about mid-June, and the beetles flocked to them immediately,” Thor said. “I just noticed the beetles on my birch tree about three weeks ago.”
Thor said her birch tree is dying a slow death anyway, so she’s choosing not to treat the tree this summer.
“If it were a healthy tree, I definitely would look into treating the tree,” she said. Throughout the summer, Thor has been spraying her annuals with an insecticide so the beetles don’t ruin her flowering annuals.
According to Allen Sommerfeld, communications coordinator for the Minnesota Department of Agriculture, the state established Japanese beetle regulations in 1992, after first detecting the insect.
The department last conducted a formal survey of the Japanese beetle in 2002, Sommerfeld said, and by that time, the beetle was detected in more than 30 counties and considered to be widespread throughout the state.
Jeff Hahn is an entomologist with University of Minnesota Extension service.
“The Japanese beetle first appeared in 1968. In the 1990s the numbers of beetles really started going up and by 1999, there were about half a million of them,” he said.
Around 2001, there were 1 million of them and 99 percent of them were found in the Hennepin and Washington counties, but Hahn can’t explain why these pests are flocking to these particular counties.
“The Japanese beetles like to feed on over 300 types of vegetation, so it’s really hard to say why these beetles favor these counties,” said Hahn. “Beetles do attract other beetles, so once they find food sources, you can bet on others showing up.”
What To Do
As far as getting rid of these pests, Hahn suggests first assessing the damage to your vegetation. For instance, these beetles tend to prefer roses, gardens, and birch, crab and linden trees, so look at these types of vegetation first.
“If it’s a low-lying vegetation, we suggest hand picking the beetles off and putting them in jars of soapy water,” Hahn said. “This kills the beetles without harming other useful insects such as bees.”
Hahn said systemic insecticides work well for certain trees if started in June, but unfortunately, it's a little late for that option. If you use insecticide, be careful not to use them on any vegetation that attracts bees.
“If you’re going to use a systemic insecticide, do not use them on blooming vegetation such as roses and flowering trees, as they are toxic to bees, and we don’t want to kill the bees,” Hahn said.
As far as controlling the insects for the rest of the summer, to kill adult beetles Hahn suggests spraying smaller trees yourself or hiring a tree service for larger trees.
Hahn said homeowners should not use the Japanese beetle traps that are being sold commercially.
“Research does not support these types of traps and it actually attracts more beetles to an area, so you are doing more harm than good,” he said. “As far as trees go, assess where the trees are in your landscaping and if the trees are an important focal point of your yard, I’d get them sprayed."
Beetles feed from July through September, so if you don’t spray your tree, be prepared to not have any leaves left by fall. The beetles won’t kill a tree, Hahn said, but after a few years of munching on foliage, it can open the tree up to disease and stress, which in turn, can kill a tree.
Trees such as birch, for instance, are stressed fairly easily anyway, and with the past couple of summers being dry, it has put some stress on the trees, Hahn said.
Bob Klatt, Woodbury’s Parks and Recreation director, said the city is seeing widespread damage to foliage due to the Japanese beetle bugs, but officials are not treating trees right now.
“The golf courses are the only areas being treated at this time,” said Klatt.
Those who opt not to treat their healthy trees this year might want to consider it next summer, Hahn said.
“With this year’s bumper crop of eggs being laid, it’s an indicator of what next year’s adult population will be,” he said.