Creative Weed Management Approaches Using Forage Crops

By Drew Lyon & By Gale Perez

In my previous position as the Extension Dryland Cropping Systems Specialist with the University of Nebraska Panhandle Research and Extension Center in Scottsbluff, I focused my research efforts on intensifying and diversifying the winter wheat-fallow cropping system. The addition of summer crops into the rotation was a first step. Inserting summer crops such as proso millet, sunflower, or corn reduced the frequency of summer fallow from every other year to once every three years. Summer crops also helped in the management of winter annual grass weeds such as downy brome, jointed goatgrass, and feral rye. As I looked for ways to eliminate summer fallow from the rotation, my attention turned to forage crops.

Forage crops are typically harvested at about 50% heading (grass crops) or flowering (broadleaf crops). This is often six or more weeks earlier than if the crops were harvested for grain. This earlier harvest provides a couple of benefits. First, it decreases soil water depletion. Water use by crops is typically greatest from the boot or flower bud stage through early grain fill. By harvesting the crop shortly after the start of this heavy water use time, valuable soil water is conserved for the following grain crop, which in western Nebraska, was often winter wheat. The earlier harvest also prevented seed production in many weeds growing in the forage crop. Taken together, these two benefits made forage crops a good alternative for summer fallow. However, there were obstacles to the use of forage crops such as a lack of forage harvesting and handling equipment and limited local markets.

When I arrived in Pullman, WA in 2012, the focus of my program shifted to weed management in wheat production systems. One of the first new weed species I learned about was Italian ryegrass. Italian ryegrass biotypes have developed resistance to eight different herbicide modes of action, which makes managing Italian ryegrass with herbicides very difficult. Some growers have turned to forage crops to help them manage Italian ryegrass.

At a Washing State University (WSU) Weed Science Field Day a few years back, we had a grower tell us that one of his approaches for managing Italian ryegrass was to plant forage barley and harvest the forage barley and Italian ryegrass before they headed and sell it in small bales to horse owners. Italian ryegrass is an excellent forage, and the bales fetched a good price. I thought that was an excellent out-of-the-box approach for managing this very troublesome weed. I could see a similar approach working for feral rye or wild oat management.

I have also noticed that some growers with Italian ryegrass issues have planted alfalfa to manage the problem. Here, Roundup Ready alfalfa could help in the establishment year, but after that, the simple act of harvesting the alfalfa before Italian ryegrass sets seed is all that would be needed. A perennial crop like alfalfa also brings other crop rotation benefits for weed control. Once established, alfalfa competes strongly with annual weeds. The seed of most annual grasses do not survive long in the soil, so keeping alfalfa in for just three or four years will significantly decrease the soil seedbank of annual grass weeds and allow a return to annual cropping with much lower grass weed pressure.

Despite the obstacles to the adoption of forage crops in our dryland cropping systems, forage crops do offer several benefits for weed management. As herbicide resistance becomes more problematic throughout the region, non-chemical approaches to weed management will become more important. I would love to hear how you have used forage crops in your rotation to manage weeds. Please leave a comment so that others can learn from your experience.