Jul 30, 2024Adding cover crops into integrated weed management programs
Cover crop adoption in the U.S. increased 17% from 2017 to 2022. While government incentives like those through the USDA Environmental Quality Incentives Program (EQIP) have encouraged this growth, the majority of growers implementing cover cropping are motivated by the role cover crops can play in improving soil health, including increased soil water infiltration (Figure 1).
However, as weed scientists, we believe cover crops can play an important role in weed management as well.
Here are four ways cover crops can be implemented into vegetable production systems with the goal of weed management. We realize that not all of these methods will work where you farm, but we hope that you will consider this a starting point.
1. Fall-planted cover crops
Fall planted-cover crops are typically planted after the cash crop is removed from the field, although in some instances growers will “fly on” cover crops into standing cash crops with drones or agricultural aircraft. From a weed management standpoint, this can serve a couple purposes. Fall-planted cover crops can compete with and suppress winter annual weeds. This has been an effective way to manage multiple herbicide-resistant Italian ryegrass (Figure 2) and occasionally glyphosate-resistant marestail.
Fall-planted cover crops can then be terminated in a way that leaves the residue on the soil surface, providing a physical barrier to weed emergence. The termination method can vary by cover crop and cropping system. The most common example from the Midwest is fall-planted cereal rye that is roller-crimped for pumpkin production.
2. Between-crop “smother cropping”
Weeds thrive in bare soil and can take advantage of the time between crops to emerge, grow, and set seeds. You can fill this void with cover crops. We’ve seen great success from buckwheat in this situation (Figure 3). Under optimal conditions, it can grow quickly and outcompete weeds. When it’s time to plant the next crop, it can be terminated with a burndown herbicide, mowing, or tillage.
3. Between row weed management
In plasticulture production systems, weeds in- between rows are often managed with cultivation and/or herbicides. Cover crops can be used in these row middles in place of herbicide. This works best for upright crops that will not grow into the row middles. In the case of our plasticulture-grown multi-year strawberry research, a row middle cover crop not only competes with weeds, but can also compete with and prevent strawberry runners from establishing in the row middles. This results in decreased hand-removal of strawberry runners in this system.
4. Cover crops as a rotational crop
In 2022, we transitioned a portion of a neglected hay field into vegetable production. After mowing, the field was plowed, cultivated, and planted with buckwheat for the summer. The buckwheat was mowed when it flowered, and the field was intermittently cultivated until early fall when a mix of vetch and cereal rye was planted. The following summer, we terminated the cover crop and planted vegetables. This provided an effective way to manage perennial weeds and forages that would have proved difficult to manage without this transition period.
Challenges and considerations
Despite the numerous benefits of cover crops, they are not without their challenges. Cover-cropped land, especially in combination with reduced tillage, can provide a safe haven for ground-dwelling mammals (ground squirrels and voles, for example), that love to eat crops and crop seeds. Cover crops can deplete soil moisture as they grow, resulting in less available soil moisture to the subsequent cash crop.
While this may be fine in a wet spring, it can be counter-productive during periods of dry weather. Cover crop residue can tie up nutrients while they decompose, resulting in necessary modifications to crop fertilizer management. All of these challenges can be managed, but they require thought and preparation.
So, is cover cropping a fit for your integrate weed management program?
Article written by Stephen Meyers and Jeanine Arana, Purdue University
Stephen Meyers and Jeanine Arana are both in the Department of Horticulture and Landscape Architecture at Purdue University. Meyers is an associate professor or horticulture crops weed science and leads a team that investigates weed-crop interactions and integrated weed management in commercial vegetable, fruit, and ornamental production systems. Arana is a Ph.D. student whose dissertation research focuses on the development a multi-year plasticulture production system, including the use of cover crops for row middle weed management and runner suppression. They can be reached via email [email protected] and [email protected].
