perrenial ryegrass vs medusa head rye

Asked September 20, 2013, 3:35 PM EDT

My husband and I bought 66 acres of dry-land pasture near John Day. It contains mostly crested wheatgrass, ryegrass, alfalfa and cheat-grass. However, our neighbors' land is about 90% medusa head and it is spreading onto our place. We now have several acres of Medusa Head on the north, south and west sides of our fence-line. I have heard that certain ryegrass species are effective in competing with Medusa Head. Is this true? If so, which species is best for competing with Medusa Head in Eastern Oregon? Thank you.

Grant County Oregon weed issues pastures and forages

1 Response

Greetings and thanks for your question. Congratulations on your purchase; the John Day area is certainly a nice place to own property. We've done quite a bit of work on medusahead control and post control revegetation of medusahead-invaded areas in southeast Oregon at the Eastern Oregon Agricultural Research Center in Burns, OR. I'll try to answer your question in two parts. First is preventing further spread of medusahead onto your property. We've found that the best insurance for preventing the spread of this annual grass is to maintain a desirable, competitive plant community. The key ingredient is such a plant community is a good cover and density of deep-rooted perennial grasses, either native or desirable nonnative species. The reason for this is perennial grasses are typically the component of the plant community that occupies a greater proportion of the rooting zone that medusahead is trying access. When these grasses are lacking from a plant community it makes resources available and exposes the plant community to invasion by medusahead and other weedy species. Now, the number of mature deep-rooted perennial grasses per square yard (here is where I put on my ecologist hat) depends on several factors, but mostly on which precipitation zone you find yourself in. On the drier rangelands (usually less than 12" of annual precipitation) that we manage in southeast Oregon on which medusahead is most invasive and problematic, we have found that 3-5 mature perennial bunchgrasses. This number would need to be larger on rangelands receiving more precipitation (i.e., resources) to limit available resources to medusahead. With that said, we found that medusahead is typically not as invasive, or at least persistent, in areas with higher annual precipitation amounts under proper management. So, preventing further spread of medusahead on your property will primarily require maintaining your perennial grasses within the plant community. Fire and grazing are probably the two most important factors that impact the persistence and natural recruitment of perennial bunchgrasses in eastern Oregon. Grazing management that incorporates periodic (every other year is probably best if the goal is maintenance of perennial grasses on rangelands), complete growing season rest from grazing (deferring grazing until after seed set of perennial grasses, i.e., not grazing plants while they are trying to actively grow) allows plants to periodically reclaim vigor and produce seed for recruitment of new plants. The impact of fire depends on fire severity. Many factors influence fire severity on rangeland, but the factor that we as managers probably have the influence over is the amount of fuel loading on rangelands, which influences fire risk and severity. The risk of fire increases as the amount and continuity of fine fuels increase on the landscape; which is one of the reasons the risk of wildfire is elevated with increasing amounts of medusahead (and cheatgrass) on rangelands. Perhaps the best tool for managing fine fuels on rangelands is grazing. Properly applied so as to maintain perennial grasses long term (see above), grazing can reduce the amount and continuity of fine fuels, thereby reducing fire risk and fire severity when wildfire does occur. There are other methods for reducing fire risk on the landscape such as green stripping (strategically planting less continuous and flammable plant communities) or annually dozing in fire breaks, but strategic grazing is perhaps most practical to apply on an annual basis. Okay, so that was a long-winded answer to the prevention part of the question, now what to do about areas that are already invaded by medusahead on your property? Again perennial grasses are the key. So, my recommendation is to prioritize control efforts and focus on areas that still have a residual perennial grass component in the invaded plant community. Establishing perennial vegetation on rangeland (dryland) can be difficult; we often simply don't get the needed precipitation at the right time. Therefore, focusing control efforts on areas that still have some established mature perennial grasses makes the most sense to me. Likely these areas lack the density of mature perennial grasses needed to exclude medusahead (that is why invasion occurred in the first place), so these areas would need to be carefully managed post control (proper grazing) to encourage an increase in the abundance of perennial grasses. Davies (2010) found that effective control of medusahead was achieved with a fall application of imazapic (6 oz per acre). Imazapic is the active ingredient in certain herbicide formulations that maintains a relatively long period of residual activity in the soil. Essentially it prevents emergence of medusahead seeds in the soil the fall it was applied through the subsequent growing season, providing perennial vegetation a chance to recover and establish if revegetation is part of the treatment. Imazapic applications are done in the fall prior to medusahead seedling emergence and when perennial vegetation is dormant to prevent injury to desired vegetation. The plant community will need to be closely monitored the growing season after imazapic application to ensure the response of perennial vegetation is adequate to prevent reinvasion by medusahead. Seeding of perennial grasses may be required during the fall after imazapic treatment if the desired response is not observed. In areas of medusahead invasion that lack residual perennial grasses, establishment of perennial grasses will be required post control to prevent reinvasion by medusahead. In this case, a fall application of imazapic at a 6 oz per acre rate followed with drill-seeding (if possible) of perennial bunchgrasses the subsequent fall can successfully control medusahead and establish a perennial bunchgrass-dominated plant community (Davies 2010). Perennial bunchgrasses need to be seeded one year after imazapic application to reduce the likelihood of perennial bunchgrasses seedling mortality from imazapic. In lower precipitation zones (8-12") we have consistently found native perennial grasses exceedingly difficult to establish following medusahead control. For instance, in southeast Oregon, areas seeded with an introduced and native species seed mix after medusahead control had perennial grass establishment of 5-10 and 0-2 plants per square yard, respectively (Davies and Johnson, unpublished data). The introduced species in this study and most studies where successful establishment has been observed on drier rangelands that I'm aware of has been crested wheatgrass. In drier rangelands, seeding with crested wheatgrass is probably the most efficient and effective strategy, but in sagebrush communities that receive more precipitation (>12”) seeding with native grasses or desired introduced species other than crested wheatgrass (e.g., bluebunch wheatgrass, intermediate wheatgrass, Idaho fescue, dryland orchardgrass, etc.) may be just as effective (Davies et al. 2011). Lastly Davies (2010) found that the effectiveness of imazapic could be dramatically improved if the persistent litter accumulation that tends to develop in medusahead invaded areas was reduced. He used both spring and fall prescribed fire treatments in his study to accomplish this. Grazing or mechanical treatments could possibly be used if using prescribed burning is not an option. Imazapic, being a soil active herbicide, works best when most of the product comes in contact with the soil. The persistent litter mat often associated with medusahead patches can act as a physical barrier that prevents herbicide contact with the soil. Therefore, reducing this litter mat can increase herbicide effectiveness greatly. If this is not an option, using a greater amount of water per acre during the application (at least 10 gallons per acre) can help carry the product down through the litter mat to the soil surface. I would encourage you to visit with your county weed control folks or cooperative weed management area to get specific recommendations on imazapic applications to control medusahead. I hope you find the information I’ve provided helpful and please don’t hesitate to follow-up with questions. Thanks again for your question and wish you the best of luck. Dustin Literature Cited: Davies, K.W. 2010. Revegetation of medusahead-invaded sagebrush steppe. Rangeland Ecology and Management. 63:564-571. Davies, K.W., C.S. Boyd, J.L. Beck, J.D. Bates, T.J. Svejcar, and M.A. Gregg. 2011. Saving the sagebrush sea: an ecosystem conservation plan for big sagebrush plant communities. Biological Conservation 144:2573-2584.