Question of the Week
Answer: Thank you for your recent request for information from ATTRA, the National Sustainable Agriculture Information Service. I am pleased to provide you with information on controlling bermudagrass in vegetable crops.
There are several options for controlling bermudagrass through sustainable farming practices. These options include fertility management, cover cropping, crop rotations, and the use of organic herbicides. I have suggested some bermudagrass control methods below and have also included information on a few good resources that you might be interested in reading related to weed management.
The use of fertilizers and amendments to control weeds is a non-conventional approach. Adherents of "weed-control-through-fertility management" draw on the concepts and practices advocated by Dr. William Albrecht and Dr. Carey Reams. Dr. Albrecht and Dr. Reams advised an approach to soil fertility based on the following:
• grassy weeds are an indication of calcium deficiency
• broadleaf weeds are an indication of improper phosphate-
Managing weeds through fertility is a long-term approach rather than a short-term solution. In other words, look for a shift in weed populations or an overall suppression of weeds after several years of alternative fertility management, but don't expect an immediate weed-free field after one application of some new fertilizer blend. For an understanding of this type of soil management, AcresUSA is a great resource (www.acresusa.com).
An example of a cultural method of reducing bermudagrass is spring tillage, as deep as 6 inches to pull up rhizomes. Rake up the rhizomes if you can and remove them from the plot. Follow this with a summer cover crop such as sorghum-sudan, closely spaced, and planted with high seeding rates. Sorghum-sudan produces a lot of biomass and can shade out bermudagrass. Tillage should be done again in the late summer or fall, and the upturned bermudagrass roots should lay on the soil surface to desiccate for a week or so. Plan this during a dry period if possible, as moisture can cause the rhizomes to sprout and continue to grow. A fall/winter cover crop such as annual rye and hairy vetch could then be planted. Rye and vetch will overwinter and continue to grow in the spring. The rye/vetch cover crop can be either tilled into the soil in the late spring. If you use annual rye as a cover crop, be mindful that rye has an allelopathic character, in that it produces a chemical that can impede the germination of small seeds. If you use rye, it is best to wait 10-14 days before planting small seeds, such as carrots. Large seeded crops are not a susceptible to rye allelopathic damage as small seeded crops. Again, be mindful that it may take two years or more to effectively reduce bermudagrass populations using these cultural controls.
Other cover crops you may choose, depending on your cropping system, are oats/field peas and buckwheat. Oats and field peas can be planted in the spring and terminated in the summer prior to a summer vegetable crop. Buckwheat is a summer crop that provides lots of biomass and can be followed by a fall vegetable crop.
Another way to get rid of bermudagrass is solarization. Placing a clear plastic sheet on the vegetable plots for 6 to 8 weeks in the heat of the summer causes the temperature to rise and kill the stolons and rhizomes. Make sure the plastic is air-tight and extends well beyond the vegetable plot to ensure adequate control. This method is most successful on smaller plots, and in areas that are not shaded.
Heavy mulching can assist in decreasing bermudagrass competitiveness. However, it is my understanding that your growing systems are mulched and that you are still fighting the bermudagrass. There are a few organic herbicides that do target bermudagrass. These herbicides use corn gluten meal as their active ingredient. For a list of these herbicides, please refer to the ATTRA Biorationals Database: http://www.attra.org/attra-pub/biorationals/.
NCCE. Cover Crops for Sustainable Production.
Available from: Chatham County Center, North Carolina Cooperative Extension, PO Box 279, Pittsboro, NC 27312. 919-542-8202. Online at http://www.ces.ncsu.edu/chatham/ag/SustAg/covcropindex.html.
Publications on Cover Crops: Benefits and Challenges, Research Review, Selecting Cover Crops, Cover Crops for Organic Farms - North Carolina State University and Center for Environmental Farming Systems, Winter Cover Crops for North Carolina, Summer Cover Crops for North Carolina, Peregrine Farm's Estimated Planting Dates for Piedmont North Carolina, Local Soil Management Grower Profiles from Peregrine Farm and Maple Spring Gardens, Sources for Untreated and Certified Organic Cover Crop Seeds, Cover Crops for Organic No-till Vegetable Production, and Web Resources.
SARE. 2007. Managing Cover Crops Profitably, 3rd Edition.
Available from Sustainable Agriculture Publications, PO Box 753, Waldorf, MD 20604-0753. (301) 374-9696. Online at http://www.sare.org/publications/covercrops.htm
"Managing Cover Crops Profitably" explores how and why cover crops work and provides all the information needed to build cover crops into any farming operation. Revised and updated in 2007, the 3rd edition includes new chapters on brassicas and mustards, six new farm profiles, as well as a comprehensive chapter on the use of cover crops in conservation tillage systems. Updates throughout are based on more than 100 new literature citations and consultations with cover crop researchers and practitioners around the country. Appendices include seed sources and a listing of cover crop experts.
Seth Kroeck. No date. Soil Resiliency and Health: Crop Rotation and Cover Cropping on the Organic Farm. Barre, MA: Northeast Organic Farming Assn.
Available from NOFA-MA, 411 Sheldon Road, Barre, MA 01005. Phone: (978) 355-2853.
This book describes the tool of crop rotation and its close relative, cover cropping, for their use in building soil in nutrient level, freedom from pest and disease and general balance and health. It is convincing as well about the financial benefits, and better use of a farmer’s time, that rotation planning can bring. Kroek clarifies the theory and practice by breaking down crops into groupings according to not just plant family, but also time of planting, time to maturity, nutrient needs and other parameters. Crop Rotation and Cover Cropping gives examples of relatively simple 6-unit rotations, along with more detailed and complex 12- and 24-unit examples.
NRAES. 2009. Crop Rotation on Organic Farms: A Planning Manual. Ithaca, NY: NRAES. Available from NRAES, PO Box 4557, Ithaca, NY 14852. Phone: (607)255-7654. Online at NRAES: www.nraes.org
This book provides an in depth review of crop rotation and its many applications, such as improving soil quality and health, and managing pests, diseases, and weeds. The authors consulted with expert organic farmers to develop crop rotation guidelines and strategies that can be applied under various field conditions and with a wide range of crops. In addition, the book includes instructions for making crop rotation planning maps using Microsoft Excel and discusses intercropping and crop rotation during the transition to organic farming.
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