The Minnesota Department of Agriculture (MDA) is warning consumers to be aware of potentially invasive weeds and destructive pests that could unknowingly ruin the holiday season this year.
Oriental bittersweet, an invasive weed that can easily be mistaken for the common decorative holiday vine called American bittersweet, has been found in the Twin Cities, Red Wing and Winona in addition to establishing its presence in many eastern states.
"We've been very concerned about the Oriental bittersweet, which has very attractive berries," said Geir Friisoe, MDA plant protection director. "People are fond of collecting those vines for garland, but unfortunately, if they sprout, they're a highly-invasive and destructive weed."
The American bittersweet is non-invasive, but the Oriental version, which is native to Asia, can turn ugly in a forest environment by strangling and smothering trees, MDA experts said. Oriental bittersweet is a prohibited noxious weed on Minnesota's eradication list, so every part of the plant is required to be destroyed.
"The invasive weed can reproduce by seeds or by rhizomes," Friisoe said. "The longer distance spreading is through birds eating them. If people are collecting berries to make garland and throw them out in the woods somewhere, they can get started there. It's really phenomenal to see. It reminds me of a bad science fiction movie."
The Oriental bittersweet can wrap around trees, Friisoe said, including large pines and oaks.
"It's like a big python, crushing the tree," Friisoe said. "The vines are so large that the weight will actually pull over the trees with time."
American and Oriental bittersweets have red fruit and look very similar but are easy to distinguish in the wintertime by the color of their fruit capsules, which surround the red fruit. The native American version has orange fruit capsules, while Oriental bittersweet has yellow fruit capsules.
"Right now, the two areas with a fairly large infestation is in the Red Wing and Waseca area," Friisoe said. "They were just discovered in Minnesota this past spring, but clearly, these infestations have been here for over 20 years, according to the number of rings that were counted in the vines."
A few small pockets of infestations were also found in the Twin Cities on highway right-of-ways.
Friisoe estimates that the problematic Oriental bittersweet accidentally got into the nursery trade at one time and hopes people learn to differentiate between the two species to prevent further spreading.
"It was being sold for a time in mail-order catalogs," he said. "People ordering from those catalogs need to be conscious of whether they're getting American and not Oriental."
The MDA encourages consumers to remove any invasive vines and treat the stumps with an herbicide.
The University of Minnesota has an Arrest the Pest Hotline (1-888-545-6684) people can call for information.
The MDA also warns about the possible spread of several forest-damaging pests such as the gypsy moth, sirex woodwasp and the pine shoot beetle, especially with the growing popularity of online and mail-order tree sales.
"In the past, MDA has found live-cut Christmas trees, indoor decorative artificial trees and even potpourri shipped into Minnesota contaminated with insects," Friisoe said.
Recently, the MDA came across Christmas trees being sold in Minnesota that came from a gypsy moth quarantine area in Wisconsin.
"Unfortunately, a lot of these trees were already sold before we came across them," Friisoe said. "We did do an inspection and were able to determine that there were no egg masses on any of those remaining trees."
The MDA is preparing a news release to alert people who may have already purchased those trees, which were sold by a parking lot dealer.
"We'd like people to take a close look at their Christmas trees," Friisoe said. "The large distinctive egg mass is fairly easy to see. They're a tan, buff color, kind of powdery-looking, and about 1 inch wide."
If infestations are found, trees should be disposed of properly, preferably by burning or chipping.