VALLEY — Mountain meadows occur in areas with deep fertile soils and good moisture. Rocky Mountain Iris’s are one of the pretty wildflowers in bloom this time of year found in these areas. Iris’s start blooming in the spring and continue on into the summer. However, they are also an invasive weed in many pastures or hay meadows.

As you drive around the San Luis Valley, Iris’s can be seen in many areas where there is a good supply of moisture in the soil. Wherever you see an Iris plant in a pasture or meadow it is almost always a Rocky Mountain Iris.

Mountain meadows grazing opportunities for livestock and wildlife can be improved by removing the Iris. A large grass response is seen when the iris is removed or reduced in a field. Grass or grass like plants is the first to recover. Which grass replaces the Iris depends on the grasses available. 

Iris is not palatable to either wildlife or livestock. The bulbs and root system is resistant to trampling when animals graze a pasture with Iris in it. The bulbs and roots also allow the plant to spread quickly when competition from other plants is reduced.

Iris control was best when 2 lbs of 2,4-D were applied during the late vegetative to late bloom stage. This seems to be the low end of the effective application range for herbicides. Research was done by applying 3 or 4 lbs of 2,4-D per acre. These treatments were similar in effectiveness of control. When less than 2 lb per acre of 2,4-D were applied the effectiveness was severely reduced. 

There are other herbicides that can be used to treat Iris. They are often more expensive and may impact more desirable plants. Some herbicides also require a “Pesticide Applicators License” to purchase. The effectiveness of these herbicides is often no better than 2,4-D when controlling Rocky Mountain Iris. 

Mowing of Iris is also a treatment option. When Iris is mowed, during the bloom stage, for several years in a row the amount of Iris is reduced. They must be mowed every year and it will take a few years before an impact is finally noticed. 

In some areas, spot treatment can be done. Whether mowing or using an herbicide Iris control must be done at the right time. Persistence is also important as a one shot treatment might not be as effective as hoped for. 

While Rocky Mountain Iris is an attractive plant, like all plants if it is in the wrong place it is a weed. By reducing or removing Iris from pastures and meadows we can increase the amount of forage for wildlife and livestock. Let’s keep our Iris’s in the flowerbed and out of the meadows.

For more information on Rocky Mountain Iris control, contact your County Weed Manager or the Colorado State University Extension Office in Monte Vista at 719-852-7381

Please feel free to visit our website at: http://sanluisvalley.colostate.edu for information about services provided.

Extension programs are available to all without discrimination. Colorado State University Extension, U.S. Department of Agriculture and Colorado counties cooperating.

References:  R.E. Eckert, Jr. , A.D. Bruner, G.J. Klomp, F.F. Peterson, Control of Rocky Mountain Iris and Vegetation Response on Mountain Meadows, USDA, ARS

J.A. Gale, D.R. Drake, T.D. Whitson, C. K. Chapman, Utah State University Extension, University of Wyoming Extension Respectively, Rocky Mountain Iris and Golden Pea Control in Pastures.

R. E Eckert Jr., Methods for Improving Mountain Meadow Communities, 1980, USDA, ARS