Using Cover Crops for Italian Ryegrass Control
For several years, cover crops have garnered considerable attention because of the benefits they provide that contribute to the sustainability of crop production. In fact, during the past several years, myriad research projects have been initiated and/or completed that provide support for cover crop use in crop production systems. For a detailed discussion of just what benefits they can provide in a Midsouth soybean production system, click here for a White Paper on this website that provides details about how cover crops can be integrated into such a system to provide those benefits.
The presence of herbicide-resistant (HR) weeds prior to planting presents a problem for those producers who choose to plant a soybean crop without any preplant tillage, and have been using herbicides to kill weeds before planting. In the above-linked White Paper, considerable space is devoted to how particular cover crop species can be used to suppress weeds that would normally be present at soybean planting. This use of cover crops has become increasingly important because of the increase in herbicide resistance that has evolved in many of the problematic weed species that will be present prior to soybean planting.
As all Midsouth soybean producers know, Italian ryegrass is a major problematic winter annual weed that has developed resistance to multiple herbicide modes-of-action, and therefore requires special consideration for its preplant control (Click here, here, and here for more information about this). Thus, alternate control measures must be used where this HR weed is anticipated to be a problem in Midsouth fields that are to be planted to soybean. This issue is addressed in an article titled “Winter cover crops reduce the soil seed bank and infestations of Italian ryegrass in no-tillage system” by Cechin et al. that appears in the journal Crop Science (2022, 62:479-488). Details about the conduct of and results from the research reported in this article follow.
• The rationale for the study was that cover crops have the potential to suppress/reduce weed infestations and the soil weed seedbank.
• The objective of this research was to evaluate the potential of several winter cover crops to suppress infestations of Italian ryegrass and the subsequent entry of its seed into the soil weed seedbank.
• Field studies were conducted for 3 years at Capão-do-Leão, Brazil (31.8 deg. S lat.; compare to St. Joseph, La. at 31.9 deg. N lat.).
• Winter cover crops–wheat, canola, barley, common vetch, cereal rye, feral radish, and black oat–were evaluated for suppression of Italian ryegrass, and compared to suppression provided by weedy fallow.
• Individual cover crop species were terminated at their seed maturity, and their residue was allowed to stay on the soil surface. Ten days after cover crop termination, soybean was planted as a summer crop.
• The study was conducted on the same area for three consecutive years using a no-till system.
• Prior to study establishment, initial Italian ryegrass density and soil weed seedbank were measured. Suppression of the weed was documented during the winter growing season of the cover crops.
• Biomass accumulation and plant height of each cover crop species were used to determine the suppression level of Italian ryegrass at the end of the 3-year study.
• Overall, cereal rye had the best combination of plant height and biomass accumulation that resulted in the greatest suppression of Italian ryegrass growth.
• At the end of the study, cereal rye, common vetch, feral radish, and black oat resulted in the lowest population density and biomass accumulation of Italian ryegrass, and the lowest soil weed seedbank of its seeds, when compared to the weedy fallow, wheat, canola, and barley cover crops.
• The authors concluded from their results that cover crops (such as cereal rye, common vetch, black oat, and feral radish used in their study) that grow tall and produce a large amount of dry matter at maturity can be used as a tool to suppress HR Italian ryegrass. They surmised this was accomplished by reducing Italian ryegrass development that can significantly reduce the number of tillers, thereby reducing weed seed input into the soil. In fact, these four cover crop species reduced Italian ryegrass infestations by more than 95% as a result of its reduced development and reduced weed seed input into the soil.
Take home message from these results: The choice of cover crop species that is used for winter weed suppression should primarily be based on the potential dry matter or biomass accumulation of the cover crop species.
Composed by Larry G. Heatherly, Mar. 2022, larryh91746@gmail.com