UNL CropWatch June 16, 2010: Controlling Scouringrush
Figure 1. Scouringrush invading a corn field from a waterway. Scouringrush patches may have stem densities of up to 100 stems per square foot.
Figure 2. New scouringrush shoots growing from the rhizome of a parent plant.
June 16, 2010
Scouringrush (Equisetum hyemale) is a prehistoric plant that is being reported as a problem weed by many corn and soybean growers in eastern Nebraska. It grows along streams, waterways, and other moist areas, but can spread from these wet areas into the drier soils of fields and pastures (Figure 1). It forms dense patches with up to 350 stems in a 2.5 ft2 area. Stands this dense will interfere with planting, choke out crops, and reduce grain or harvestable forage yields.
Scouringrush is closely related to ferns and is believed to date back about 280-345 million years. It is in the Equisetum (horsetail) family. It is a perennial and has hollow green stems that grows to a height of 2-4 feet (Figure 2). The stems are segmented, stove pipe-like in appearance, and easily pulled apart at the nodes. Normally there are no branches or leaves, although some branching may occur at the nodes if the stems are damaged by mowing or certain chemical treatments. A spore-producing cone (Figure 3) that is yellow to brown forms at the top of the stem mid summer. Scouringrush has deep fibrous roots and extensive rhizomes. It spreads primarily by rhizome, although the spores are also believed to be fertile.
Scouringrush is called by many different names, including snake grass, jointed grass, horsetail and horsepipes. It gets its official name because its rough stem was used by pioneers to scour pans. The stems contain high levels of silica. Livestock that graze it heavily may experience scours, paralysis, abortion, and in rare cases, death.
Nebraska Herbicide Management Trials
We conducted research measuring scouringrush response to herbicides, mowing, and tillage in 2006-2008. We evaluated 24 herbicide active ingredients, individually or in various combinations, but only two (chlorsulfuron and dichlobenil) provided commercially acceptable control of scouringrush (Tables 1-3). Unfortunately, neither chlorsulfuron nor dichlobenil is labeled for use in corn or soybean.
Chlorsulfuron, labeled as Glean for use in wheat, or as Telar for use in non-crop areas, was very effective at controlling scouringrush for more than one year when it was applied at 3 oz /ac. Chlorsulfuron has a long soil residual and can cause significant injury to corn and soybean. The maximum use rate in wheat is 0.33 oz/ac (approximately 10 times less than what we applied), and the rotation interval to corn or soybean is 24 months. If chlorsulfuron were used to control a scouringrush patch that is expanding from a non-crop area into a corn or soybean field, only plant an IR-corn or STS soybean in the treated area in the subsequent three to five years. Even at that, you may still suffer some crop injury from herbicide carryover.
Dichlobenil is a herbicide used for weed control around woody plants and herbaceous perennials. It provided excellent control for at least one year; however, dichlobenil is not labeled for use in corn or soybean. It has very high use rates (150 lb/ac), and is most effective when it is incorporated by tillage.
Glyphosate was not effective at controlling scouringrush in our studies (Tables 1 and 2), and this is consistent with glyphosate performance on other Equisetum species (Torstensson and Borjesson. 2004. Pest Management Science 60:565-569).
Tilling an area will reduce stem and biomass measurements temporarily, but if other control tactics are not used, the stand will soon regain its earlier density. Repeatedly mowing an area also has little long-term benefit. We have received reports that deep tillage (moldboard plowing) can reduce stands. The best non-chemical approach to controlling scouringrush is likely deep-tilling an area and then immediately planting it to corn or a high population of soybean. Scouringrush is not competitive under dense canopies or in low light conditions. This aggressive management approach will likely need to be repeated for several years to eliminate or minimize a patch.
There are two cautions regarding tillage. First, the benefits of controlling scouringrush using deep tillage should be weighed against the risk of soil erosion along a waterway. Second, tillage, especially shallow tillage, can expand a scouringrush patch. Because scouringrush reproduces primarily by rhizome, if the tillage operation moves the rhizomes beyond the area of the original patch, new plants can form and the patch can grow larger. Scouringrush shoots can form from small sections of rhizomes, even when they are buried 6 inches or more.
Little information has been reported on scouringrush biology and control. Based on literature describing research on field horsetail (a closely related species) and observations in 2008-2009, we believe that tillage may be more effective if it takes place in the spring or first part of the summer while the shoots are still growing, and herbicides may be more effective after shoots stop growing mid-summer and rhizome growth accelerates. We hope to have more information in future years to share about how to best manage this ancient plant.
Extension Weeds Specialist, Lincoln
Former Graduate Student, UNL Department of Agronomy and Horticulture
Extension Educator, Weed Science, Lincoln