By CELESTE BAUMGARTNER
Ohio Correspondent COLUMBUS, Ohio — Giant ragweed is a native annual plant which produces few seeds – yet, as farmers well know, is an entirely successful weed. Researchers at The Ohio State University found that part of its success may be caused by a surprising culprit: Earthworms.
When the ragweed seeds are on the ground, most of them are eaten by mice and completely destroyed, said Dr. Emilie Regnier, OSU weed ecologist. In looking for ways that the seeds escape from predators, the researchers made an interesting observation.
“We saw that the seeds were being moved around ... and to a sort of disbelief, we saw that the earthworms were taking the seed from the surface and burying them in their burrows,” she said.
That’s how the research – conducted in Ohio, Indiana and Illinois – started, Regnier said. They wanted to learn what the effect was on giant ragweed and how active the earthworms, specifically night crawlers, were in gathering the seeds.
It is well known that earthworms, usually considered the “good guys,” collect leaves that they stuff into their burrows; these burrows then act as mini compost heaps.
“Earthworms are beneficial in recycling nutrients into the soil, causing faster breakdown of litters, and that’s beneficial to the soil,” Regnier said. “Their burrows, which are permanent, create channels for air and water and roots to follow, so that’s quite beneficial.”
While earthworms are known to swallow and disperse tiny weed seeds, giant ragweed seeds are large – they can be up to half an inch. The way earthworms forage is by leaving their tail region in the burrow and skimming the soil surface with their anterior region, or the mouth, Regnier said.
Once they get a firm grip on the seed, the earthworm withdraws into its burrow and drags the seed with it. The critters are so stretchy that they can snake out about a foot or up to 18 inches from their burrow.
Why the earthworms want the ragweed seeds, which are too big for them to swallow is “the question of tantalizing interest,” Regnier said. They line their burrows with the seeds and even put them in little side chambers off the burrow near the top of the soil.
One hypothesis is that the earthworms might graze on the woody hull of the seed as it decomposes, she said. Also, earthworms enter a chamber and go into a quiescent period in winter and summer, Regnier said. They line that chamber with pebbles. It is possible they are using giant ragweed seeds as a structural support.
Why the earthworms store the seeds is a mystery, but that they do it is a fact.
“Our study shows that night crawlers are some of nature’s most effective weed farmers, Regnier said. “They actively forage for weed seeds, pull them into their burrows and then ‘plant’ them under up to several inches of soil.”
Researchers are interested in seed predation – that is, not tilling the soil so that weed seeds are left on the ground surface for mice, beetles or birds to destroy, Regnier said.
However, if there are earthworms in the field, chances are they will get a large proportion of the seeds and protect them from predation by putting them in their burrows.
It’s important for farmers to be aware of this and to not allow the seeds to mature, Regnier said.
The research was funded by USDA’s Cooperative State Research, Education and Extension Service. The researchers included Regnier, weed ecologist Dr. Kent Harrison and entomologist Dr. Clive Edwards, all of OSU.
The Weed Science Society of America issued a press release on the research in which Lee Van Wychen, policy director, stated: “Giant ragweed should be vigorously controlled in fields and gardens in order to minimize further seed production and protect plant growth and crop yields.”
For more information, visit www.wsssa.net |
