With more and more weeds becoming resistant to herbicides, many experts are recommending a return to a set of practices called integrated weed management (IWM). Like integrated pest management, IWM relies on the biology of the pest—in this case, the weed—to reduce weed populations to manageable levels and prevent future weed introduction. IWM refers to the integrated use of cultural, physical, biological and chemical control strategies to contain or eradicate a population of weeds.
Because IWM is a broad topic and includes a variety of possible practices—from hand-pulling to hoeing to mulching and cover cropping—this post will focus on one aspect of IWM: good soil management.
Organic farmers know the importance of maintaining good soil balance, especially since they don’t have a chemical arsenal at hand. Of course, having good soil doesn’t always deter weeds; many weeds love a nutrient-rich soil as much as flowers and vegetables do. The trick is to cultivate the soil around the plants you want to grow and maintain a temporary deterrent for the plants you don’t want, until your crop grows large and strong enough to shade out potential weed seedlings.
According to Dr. Mary Peet, currently the USDA NIFA National Program Leader for the Integrated Organic Program, good soil should be well drained, have a deep rooting zone, be easily penetrated by air, water and roots, have a good water-holding capacity, have a balanced nutrient supply and resist erosion.
Scientists have a variety of theories on how to enrich soil and reduce weeds, and most theories depend on the individual site. Many growers use cover crops, a crop that grows between regular crop seasons to infuse the soil with natural chemicals that are toxic to many weed species. Ryegrass and buckwheat are two common cover crops.
Crop rotation is another technique that discourages weeds and pests by introducing a new crop species incompatible with the pest that has been feeding on the crop. Growers choose crops that complement each other, either by contributing nutrients that the next one needs or by extracting nutrients before they build to high levels. Rotation pairs also tend to need similar tillage and care, so no additional equipment is necessary to take care of the second crop. Crop rotation can also discourage weeds that tend to grow with the same crop year after year. In Oklahoma, for instance, many wheat growers are rotating with canola to discourage grassy weeds that typically accompany the wheat.
According to an article by Mark Schonbeck of the Virginia Association for Biological Farming, weed control is most important during the early stages of crop development. Good weed management allows the crop to develop to a stage where it can outcompete developing weeds. Weeds that grow faster and more robust than a crop can affect yields, often significantly.
Weed and soil management success can vary based on crop variety, as researchers in Michigan report in a paper published in HortScience in 2009. Scientists tested three soil management techniques in apple orchards: mulching with alfalfa hay, flame burning and a Swiss sandwich system. While each technique had advantages and drawbacks, the Swiss sandwich system—a strip of vegetation between two crop rows—worked best for a specific rootstock of ‘Pacific Gala’ trees. The alfalfa hay mulch treatment created the best soil conditions for ‘Pacific Gala’ trees and improved the appearance of all trees, regardless of rootstock or variety. However, it was one of the most expensive.
To learn more about integrated weed management, call the IPM program or local extension office in your state.
Filed under: Crop rotation, Weed Control Tagged: | Crop rotation, organic weed management, resistant weeds, soil management, weed control
