The use of straw mulches and manure fertilizers can be either a boon or a problem, when it comes to weed management. A good mulch will save many hours of weeding through the summer months and it can eliminate the need for herbicides in those areas. And good manure fertilizer can boost plant vigor and yield, releasing the needed nutrients at a steady rate throughout the growing season and adding that all-important organic matter to the soil.
However, the down side of these materials is that they can contain long-residual herbicides. The presence of toxic residues can occur in mulches or manure if herbicides were used when raising crops or if cattle fed on crops that contained those herbicide residues. When you use straw or manure that has been produced under those conditions, the residual herbicides can damage the plants with which they come in contact.
You can avoid the problem altogether by simply asking the grower if herbicides were used that might have left residues in the straw or manure. Many herbicides, such as Roundup, break down quickly and do not have residual action after several weeks. Other herbicide residues, such as picloram (Tordon) can affect plant growth for several years. In most cases, the straw or manure will contain no residues, so continue to use these environmentally sound methods of weed and nutrient management; just ask before you buy.
One last thought; if herbicides were not used by the grower, be aware the
materials might contain weed seeds that can germinate in your field,
introducing serious perennial weeds that are extremely difficult to control, or
annual weeds that are prolific and can cause problems for years to come. Again,
the grower can help you determine if this could be a problem.
References:
Controlling Pests and Diseases; Rodale's Successful Organic Gardening. 1994. Rodale Press, Emmaus, Pennsylvania 18098. 422 pp.
Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608- 1239. Pub. #3332. 276 pp.
Olkowski, W., S. Daar, and H. Olkowski. 1991. Common-Sense Pest Control; Least-toxic Solutions for Your Home, Garden, Pets and Community. Taunton Press, Newtown, Connecticut. 715 pp.
Disclosure. Common chemical and trade names are used in this publication for clarity by the reader. Inclusion of a common chemical or trade name does not imply endorsement of that particular product or brand of herbicide and exclusion
Categories: Weed, Integrated Weed Management, Herbicide Residue
Date: 04/28/2005