County takes first step in biological control for pesky weed
As a former horticulturist and current noxious weed agent for Washington County, Duane Bruna has a history of battling bindweed. It goes way back into his childhood on his dad’s farm, where bindweed was ever-present. Chemicals knocked it down, thinned it, sickened it, even killed some of it, but like a Timex watch it took a licking and kept on ticking.
That might change in the near future. Bruna and the other agents of the county noxious weed department have implemented the first phase of a trial planting of bindweed infested with Aceria malherbae, the bindweed mite.
“It sounds crazy,” Bruna said, “but I’ve been watering bindweed.”
Planting it, too. On August 17 at 3 p.m., Bruna, with Larry Leck and Brian Kolle, planted seven six-inch pots of mite-infested bindweed within a six-foot circle in an undisclosed location. The test plot had to remain undisturbed and not sprayed for two years. “I picked an area I could kind of control,” Bruna said. They watered the seedlings the next day, and returned two days later for another dousing. Rains the following week did the work for them. Now they’re watching, and waiting, for what promises to be a very long and very slow process.
Field bindweed has been a problem for agriculture since the first Europeans settled in America. Like other non-native invasive species, once established it spreads fast through seeds and lateral roots, or rhizomes, some of which can reach a depth of 30 feet. That makes the use of mechanical or chemical control nearly hopeless. Plus, seeds can remain alive for as long as 60 years. Studies have shown that bindweed’s root and rhizome mass can reach two-and-a-half to five tons per acre.
So cosmopolitan is it that it’s earned 84 names in 29 languages, most of them unflattering. Its Latin name, Convolvulus arvensis, “to entwine, of the fields,” is derived from its nature, though it’s commonly known as wild morning glory, creeping jenny and other names, some of which can’t be printed in a newspaper.
According to the Kansas Department of Agriculture, an estimated 1.9 million acres in Kansas were infested with bindweed during 2005, making it one of the most damaging invasive species of non-native plant.
Chemical agents have been developed to control bindweed, but are generally nonspecific to one plant. In an effort to reduce the amount of toxins in the soil, researchers have begun to look for biological controls, using living organisms to control pests, whether insect or plant. In 1989, bindweed mites were imported from southern Europe by the Texas Agricultural Experiment Station in Bushland, Texas, and various control studies have been implemented in Texas and New Mexico since 2000.
In Kansas, the Field Bindweed Biocontrol Program was instituted in 2006 by the Kansas Department of Agriculture, with assistance from the K-State Department of Entomology. When Bruna heard of it, he immediately wanted to be a part of it.
What he wasn’t expecting when he picked up his plants in Manhattan was what appeared to be a complete absence of mites. He had expected them to be small, along the lines of spider mites, tiny insects best found by placing a white sheet of paper beneath a plant and shaking them loose.
“You can’t see them with the naked eye,” he explained. But the plants looked sickly, with shriveled leaves that folded in on themselves. “They looked bad,” he said, and it was evident in his voice that he wasn’t too upset by this.
Withering is the main symptom of mite infestation in bindweed. The mites are microscopic and cause gall-like formations on plant leaves. In heavily infested plants, shoots are misshapen and growth is stunted. Recently infested plants have newly emerged leaves that appear folded, thickened and with a fuzzy texture. All are indications that mites are active.
Transferring mite-infested plants to non-infested areas is as simple as breaking off plant parts such as vines and twisting them around other vines. Once the plants within a controlled area are infested, in ten days to two weeks, they can be moved around by mowing the weeds, which spreads the infestation.
If the mites take over and kill the bindweed in the test plot, Bruna said his crew will transplant some and plant at it different locations, or wherever the state tells us to.
Questions invariably arise over the ethical use of biological controls. Introducing a new species to a different biota can occasionally have disastrous results, as in the 1970s when the USDA released the multicolored Asian lady beetle to combat tree-climbing aphids affecting pecan orchards in the southeastern U.S. At first they did a superb job—so superb that native species of ladybugs were left with too little to eat. That the new lady beetle had wanderlust exacerbated the problem for much of the rest of the country, and they were even responsible for the extinction of New York’s official state insect, the nine-spotted lady beetle. Endemic birds in Hawaii have suffered tremendously after mongooses were introduced to kill rats. And the release of rabbits in Australia is blamed for one-eighth of that continent’s mammal extinctions.
One problem with biological controls is that once they’re released, there’s no way to round them up. Though somewhat cautious, Bruna said enough studies have been done to prove the mites safe.
“The mites are a biological control,” he stressed. “They won’t be perfect. They’ll be a help but not a hundred percent solution.” Nor does he think they’ll ever be the only source of bindweed control. “I think using sprays and mites together will be necessary,” he said.
And even so, considering the long history of mankind’s war on bindweed, he remains philosophical on our chances of eradication. “Bugs and weeds have been here before us and will be here after us,” Bruna said. “Our lifetimes are short. What we need to do is manage them. Will we get rid of bindweed? Not in our lifetime. There’s some that always gets by. But—I like a challenge.”
The question now is whether they can over-winter successfully. The mites spend winters beneath the ground on bindweed rhizomes. Prior tests have shown them capable of surviving winters in Canada and Montana, so Kansas should not be a challenge. “If they over-winter and survive,” Bruna said, “they’ll help us.”
One environmental factor that might limit the success of bindweed mites is excessive moisture. Studies have shown the mite to be more effective in arid climates, which Washington County can hardly lay claim to.
For now, nothing is certain. The mites have been planted and autumn is approaching. The noxious weed crew waters the test plot and keeps an eye on the plants for signs of damage. Next spring, when bindweed begins creeping from the soil, they’ll know a little more. But it will still be decades, Bruna thinks, before the mite becomes a regular part of our arsenal against weeds.
But, he said, it’s a start. The real problem he’s struggling with is the idea of cultivating his old nemesis. “My dad would spin in his grave if
he knew I was planting bindweed,” Bruna said.