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 organic control methods for common milkweed.
Common milkweed, Asclepias syriaca, is a perennial plant that commonly grows in patches. It prefers dry soils and is often found in woody areas, along roadsides, and in gardens and fields, especially if they are unmowed. Milkweed is a good source of nectar for pollinators and is a major food source for the monarch butterfly. Yet, common milkweed is considered a noxious weed in many regions of the U.S., particularly in the east. Milkweed can be toxic but common milkweed tends to have less toxicity than many other milkweeds. In fact, the toxicity levels are dependent upon certain conditions. As a noxious weed, milkweed can reduce crop and forage yields. If milkweed stands are not controlled, they become more established and the economic impact increases over the years.
Common milkweed spreads by rhizomes and by seeds that are carried by the wind. There are no approved biological or chemical controls for common milkweed that are acceptable in organic production. Therefore, controlling common milkweed is a challenge. Since it can spread by rhizomes, cultivation is not an effective control method as each root segment can regenerate a new plant. Even minimum tillage can increase common milkweed populations. Common milkweed can be confused with hemp dogbane (Apocynum cannabinum), which also spreads by seed and rhizomes. However, hemp dogbane can be controlled through flame weeding. Flame weeding is not effective for common milkweed and can actually stimulate new growth. The burning of young seedlings and dead stalks causes new growth to have taller straighter stems with longer fibers. It also stimulates flower and seed production.
There are a few suggested organic control methods for common milkweed. Pulling or digging up plants is effective, getting as much of the root system as possible. Hoeing or cutting the shoots every week or two will reduce and possible stop the plant from resprouting as well as reducing the root reserves. This can also be done by repeated mowing every three weeks. Further, adding a dense mulch layer can be effective once the plants are cut down. Please note that if you are planning on composting the plants and roots, they should be thoroughly dry so that they do not resprout.
In addition to these control methods, organic soil fertility management will also help reduce common milkweed populations. This involves proper crop rotations and the use of cover crops. Below are three resources on organic soil fertility management that may be of interest to you. All three books are available for purchase through SARE (www.sare.org).
Clark, Andy (editor). 2007. Managing Cover Crops Profitably, 3rd Ed. Beltsville, MD: SAN Publication.
- explores how and why cover crops work and provides all the information needed to build cover crops into any farming operation
Mohler, Charles and Sue Ellen Johnson (editors). 2009. Crop Rotation on Organic Farms: A Planning Manual. Ithaca, NY: NRAES.
- provides an in-depth review of the applications of crop rotation-including improving soil quality and health, and managing pests, diseases, and weeds. Consulting with expert organic farmers, the authors share rotation strategies that can be applied under various field conditions and with a wide range of crops.
Magdoff, Fred and Harold Van Es. 2000. Building Soils for Better Crops, 3rd Ed. Waldorf, MD: SARE Publication.
- a practical guide to ecological soil management; provides step-by-step information on soil-improving practices as well as in-depth background.
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