Cereal Rye Cover Crop for Pigweed Management
Cover crops [CC] should be considered an integral part of any cropping system that seeks to become more sustainable and supportive of conservation agriculture. Cover crops are grown in most cropping systems to provide environmental and soil productivity benefits. Click here to access a White Paper that provides details about how CC’s can do this.
With the advent of herbicide-resistant [HR] weeds in recent years, CC’s are now being promoted to aid in the management of these weeds. In particular, a cereal rye [CR] CC that precedes soybean planting is being touted as a tool that can be used to manage problematic weeds in U.S. crops.
A 2024 article titled “Planting soybean green: how cereal rye biomass and preemergence herbicides impact Amaranthus spp. management and soybean yield” reports results from research that was conducted to evaluate the feasibility of planting soybean green on two dates when integrated with PRE herbicides for the control of pigweed. Details about and results from the research follow.
• [Planting green is the practice of planting the cash crop–in this case soybeans–into a living CC vs. one that has been terminated/killed 1 to 2 weeks before soybean planting].
• Weeds of the genus Amaranthus [includes Palmer amaranth or pigweed] are the most problematic weeds in soybean cropping systems across multiple regions of the U.S.
• Cereal rye is the most common CC used by U.S. farmers for weed suppression because of its high biomass production. However, if CR is terminated before accumulating the level of biomass needed for weed suppression, it will not provide the desired benefit. Thus, management practices that delay CR termination should result in a greater amount of biomass accumulation.
• Regardless of how CR is managed to accumulate maximum biomass, it alone is unlikely to provide adequate control of problem weeds in soybeans. Thus, combining a CR CC with the use of PRE herbicides is perceived to be a viable integrated weed management [IWM] approach.
• Field studies were conducted in 10 states [including Arkansas, Kansas, and Missouri] during the 2021-22 growing seasons.
• The following three factors were used in the study: 1) early and late planting of soybean [early planting occurred as soon as conditions at a site allowed, whereas late planting occurred an average 17 days after early planting at a site]; 2) CC management practices of no-till [no CC], early termination of no-till-planted CR [CR chemically terminated an average of 13 days before soybean planting], and soybean “planted green” into CR that was chemically terminated at soybean planting; and 3) either a PRE herbicide applied at “plant green” termination time or no PRE.
• Both “plant-green” and late soybean plantings resulted in large increases [33% and 41%, respectively] in CR biomass compared to that from early soybean planting and early CR termination.
• Planting soybean into “green” CR resulted in the greatest CR biomass and the lowest pigweed density of the three practices shown in 2 above. Thus, weed suppression was associated with CR biomass production.
• PRE treatment reduced pigweed density in both the early and later plantings.
• The higher biomass produced by the CR in the “planting green” system combined with an effective PRE herbicide application to soybeans is likely the best IWM approach for pigweed suppression.
• Selection and proper setup of the planter that is used to plant soybeans “green” will be of paramount importance if this system is adopted by soybean producers. Also, producers should be aware that seeding rates may need to be increased if soybean stand from a common seeding rate is reduced by the greater CR biomass in this system.
Click the above-linked article for additional details about the study, and here for a video presentation about planting soybeans into “green” CC’s.
Composed by Larry G. Heatherly, Jan. 2025, larryh91746@gmail.com