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Fighting invasive species

By Staff | Apr 15, 2011

Teasel, an invasive species, grows wild along a drainage ditch on the east edge of Fort Dodge.

FORT DODGE – Invasive species are constantly changing the native ecosystem, but Bill Johnson, of the Iowa Department of Natural Resources, wants to help landowners in a fight to restore native plants to Iowa’s grasslands.

Johnson, who addressed a habitat workshop for landowners in Fort Dodge on April 1, raises native grass and wildflower seed for the DNR at Brushy Creek State Recreation Area. He said there are more than 100 species in production there.

The goal of the DNR is to maintain its areas in a natural state, and when there are invasive species, it changes the ecosystem by replacing the native species and competing with them.

“Invasive species gain a foothold, they prosper and they replace the native species, the ones that were growing here naturally, that were here before human settlement.

“There is a tendency for people to think that if something’s new, it’s better,” Johnson said. “What we have here naturally is adapted to these conditions, and one of the problems with bringing in that new stuff is that while it may grow in a similar climate … they bring the seed over, but they don’t necessarily bring the critter that keeps it in check.”

CROWN?VETCH, an invasive species, was originally used for controlling weeds along road ditches.

There is a rule of 10, Johnson said.

“One out of 10 plants that you bring in from somewhere else becomes established. They may not be a problem, but one out of those 10 becomes invasive,” he said. “So basically, one out of 100 plants will become invasive that you bring in from outside.”


Canada thistle – “This is the big one, the one most farmers have dealt with. No. 1, it’s a perennial; No. 2, it grows vegetatively. So, you may kill the above-ground growth, but it has lateral roots that will come up in future years,” Johnson said.

In a prairie situation, there is only one strategy to control it, he said. The prairie basically goes dormant after a frost, but Canada thistle doesn’t, so spraying herbicide after the frost is effective. Also, because the thistle is translocating all of its energy from its leaves to its roots at that time, it also translocates the herbicide.

However, there are downsides, he said. It’s cold in the fall, and many co-ops that do spraying have already stored their equipment for the year.

Leafy spurge (Euphobia esula) – “This is another tough one,” Johnson said. “I used to think it was a western Iowa species until I relocated to Webster County about five years ago. It’s all over Webster County. There are a couple of herbicides that do a fairly good job of controlling it, but it is a tough one to ever get rid of.”

Sweet clovers (Melilotus officinalis, M. albus) – For the most part, in low-level populations, sweet clover isn’t a problem species, Johnson said, but it can get to a point where it takes over a system. It’s a biennial, non-native legume that likes burning. So, if burning is part of a farmer’s CRP mid-contract management strategy, two years later, the sweet clover will make its reappearance.

The best and easiest strategy, he said, is “when it gets to the flowering stage, mow it or cut it off. Once it’s flowered, it’s completed its life process and will basically stop. There next year, it won’t be there.”

Wild parsnip (Pastinaca sativa) – “This is a coming problem all over the state,” Johnson said. “You see it in road ditches quite a bit, disturbed areas. This one you can also do mowing to get rid of, or I believe you can spray it in the fall in the rosette stage.”

In small populations, it can also be dug out with a spade, he said.

Crown vetch (Coronilla varia) – “This is another you see a lot in roadsides because 20 years ago, it was used to control erosion in road ditches. But they found out it really didn’t,” Johnson said. The good news is that it isn’t mobile; it slowly invades. It will, however, dominate 100 percent.

“It’s also a legume, so it likes fire. So, if you burn this one, sometimes you will invigorate it,” Johnson said. “But, it’s easy to control with spray. The downside is, because it is a legume, the seed lasts a long time. You can spray the existing plants out, but there will be a number of those seeds that will survive and come up in future years. This may not be a one-and-done proposition when you spray; it may be over several years.”

Birds foot trefoil – It’s used for pasture improvement, very similar to crown vetch, he said. Since it’s also a legume, the same strategies will kill it. Unlike crown vetch, Johnson said, birds foot trefoil will not dominate a system.

Sericea lesperdeza, L. cuneata – This plant is primarily a southern Iowa problem, he said, because it sets seed really late in the fall and Webster County is on the edge of the seed-maturing stage for the species.

Teasel – Because teasel has a “pretty little seed head,” it’s often used in dried flower arrangements, which explains why it’s often found near cemeteries. “The decorations they put on the graves blow off and into the neighbor’s field, and you get a population of teasels. It’s not a terrible problem to control. It’s a coming problem and it gets spread by mowers,” Johnson said.

Pampas grass – “A lot of people see these light, feathery seed heads and think, ‘Ah, it’s a beautiful thing; I’ll put it in my yard,'” he said. However, it grows vegetatively and with lateral roots. “So, the nice little clump that you started will (take over) the whole road ditch.”

Spotted knapweed – “This is more of a western species that gets transported by hay a lot.”

Reed canary grass – “This one is kind of interesting because it is a native species,” Johnson said, but apparently a hybridized composition of the plant got released and has become very aggressive. “It takes over areas, especially flood plains or very moist areas.”



For success in growing native flowers, Johnson said, they need to be planted in their dormant time.

“They have a seed coat on them, and if you think about it, if a prairie flower seed drops in the fall on the ground and germinates, it would get about so big,” he said, measuring a couple of inches high with his fingers. “And when the frost comes around, it’s going to die. Our native prairie plants have adapted a strategy to get around that. Before that seed germinates – if it drops in August, September or October – it has to go through a cold period first – winter because that’s what we have here in Iowa.”

Another plus with native plants, Johnson said, is that they don’t have to be fertilized or watered once they’re established because they have adapted to Iowa conditions.

Most prairie wildflowers are cool season plants. Since most of them haven’t emerged at this time of year, this would be a great time of year to burn, he said. “Fall is a good time to burn, but I like to see the habitat out there, the winter cover. If you have forbs in the mix, try to burn early; if it’s just native grasses, you can burn any time.”

Johnson also suggested some native species that would be desireable in a seed mix.

Butterfly milkweed – “It’s fairly high-priced seed, but it’s a pretty easy seed to grow.”

Prairie blazing star – “It’s one of my favorite plants in the prairie,” he said. “It doesn’t do very well in your garden or around your house. It needs companions. If you plant it around your house, it gets about 8 foot tall and falls over. In the prairie, where it has competition, it’s a beautiful plant.”

Blue-eyed grass – “This is actually an iris, and it gets about 6 to 8 inches tall. It’s a great one to plant around your house,” and likes lots of sun.

Bottle gentia – “This one actually likes a little bit of shade,” he said. “They’re really, really expensive seeds but you don’t need many seeds. This is a nice one to grow in wet areas.”

Prairie dropseed – “This is the native grass that has the most potential for wildlife, and it has the most potential to use around your house,” Johnson said. It’s a finely leaved grass that looks like a fountain and has a seed head that comes up in the middle. It grows about 18 inches high.

“The downside,” he said, “is when it’s pollinating, it has an odor that’s not pleasant.”

Ground plum – A native legume, it grows on dry hillsides on the prairie. “It’s great for CRP mix, and it’s great around the house, too,” Johnson said. “It’s got a really interesting bright red fruit that looks like a plum, but it’s actually a bean.”

Purple prairie clover – It’s another easy-to-grow, native legume, he said.

Pale purple coneflower – While purple coneflower is native to only about five or six Iowa counties, pale purple coneflower is native to the entire state, Johnson said.

New England aster “This is another one that’s easy to grow. It flowers in the fall or late summer,” Johnson said. It is extremely attractive to deer, which can work two ways, he said. It can draw deer in – for those who want to do so or it can lure them away from other plants.

Prairie onion – This species is native to northern Iowa. “It smells like an onion and has a beautiful flower in the fall or late summer,” he said.

Contact Barbara Wallace Hughes at (515) 573-2141 or bwh@messengernews.net.

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