Tom's Blog

Wednesday, February 22, 2012

Control of smooth brome and other clonal grasses

I have posted on this topic in earlier years, but it deserves repeating. Now is the time to think about using the technique described below.

Smooth brome (Bromus inermis) is one of the more persistent problems in any restoration in our area. Any former ag field that remains fallow for any length of time is soon taken over by it, or by quack grass or some other grass that spreads by rhizomes. Roadsides also become dominated by such grasses.

Although some sources state that smooth brome can be controlled by carrying out late spring (May or later) burns, we were never able to eradicate it that way. However, we have been very successful in eradicating it without damaging native plants by carefully timed herbicide (glyphosate) treatment.

The principle of this method, first suggested to me by Jim Sime, is based on the fact that smooth brome is a cool-season grass and appears quite early in the spring, long before any native species are evident. The herbicide glyphosate has the useful characteristic that it is completely inactivated by soil particles so that there is no residual activity. Only plants that are above ground will be affected. If it's green it will be killed. Timing is critical, and leaves about 4 inches tall are ideal.

The technique works very well, and we have used it in four of our planted prairies (Barn, Crane, Ridge, and Valley), as well as at the Gateway Prairie at Black Earth Rettenmund State Natural Area. Also on the road cut of Pleasant Valley Road.

For small areas, Kathie and I have used backpack sprayers, but for fields or roadsides it is much cheaper to have the local agriculture co-op come in with a big boom sprayer. At least in our area (Premier Cooperative) they have been very helpful and will come on a day's notice.

Because the weather varies from year to year, it is essential to monitor the target site carefully. The first of April or the last few days of March have been ideal in our area of southern Wisconsin. The photo below shows the Barn Prairie being sprayed. This was the first prairie we sprayed and I think it should have been treated a few days earlier, as it looks a little lush. In fact, golden Alexanders, one of the early prairie plants, was set back noticeably by this treatment, although it was fine the following year.
Roadside spraying is where the co-op rig really comes into its own. As the photos below show, the rig has a long boom. The operator is a whiz at moving it around all the small trees and signs. The whole half-mile-long road cut here was sprayed in about 15 minutes, a task that would have taken hours or days with backpack sprayers.

The roadside spraying was done in 2005 and was very effective. Smooth brome died and left mostly bare soil. A week after spraying, the whole road cut was planted with a mixture of prairie grasses and forbs, and we planted again the following year.

A view of this roadside five years later (2010) is shown below. Smooth brome is virtually absent, and the site is dominated by little bluestem. Earlier in the season, before the grass takes over, this roadside is lush with prairie forbs.

There is one downside to this technique, although it can be rectified. Some prairie species, such as thistles, overwinter as vegetative rosettes, and will be killed. Indeed, we lost swamp and pasture thistle virtually completely when we treated the Crane Prairie. However, since these are both biennials, they establish well from seed, and can be replanted a few days after spraying.


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