To Manure or Not to Manure

Russ Poston
Home & Garden Information Center

Many homeowners consider manure to be a safe, organic fertilizer for use in the flower or vegetable garden.  The belief is that manure is something that is naturally produced, and therefore, is a safe product to use. So why is it that after application of some manures, plants show symptoms of damage? These symptoms can include leaves that are twisted, cupped and elongated; fruit that is deformed; reduced yield; death of young plants; and poor seed germination.

The possible cause of the damage is the presence of certain herbicides in manure and compost. These herbicides are in a class known as pyridine carboxylic acids. Some examples of these are aminopyralid, clopyralid, picloram and triclopyr. They are used to control a range of broadleaf weeds in pastures, grain crops, lawns, some vegetables and some fruits. These products don’t harm the animals grazing or eating the hay from pastures. The problem arises because some of these chemicals are persistent and can remain active even after passing through the animal. The chemicals can be present in the hay, grass clippings, straw and manure, even after being composted. Some of the herbicides degrade quickly, but aminopyralid, clopyralid and picloram may take 3 or more years to become inactive. The problem arises when the manure or compost is applied to areas where vegetables or flowers are to be grown. The vegetables and flowers that show the most sensitivity are tomatoes, potatoes, lettuce, spinach, peas, beans, dahlias and some roses.

The best way to deal with this problem is to know more about your source of manure. If you raise animals and feed them hay, ask the person who produced the hay when and what herbicides were applied to the field. If you are getting manure from a farmer, ask about the source of the hay for those animals, what was fed to the animals and what herbicides were applied to the fields. If you are unable to get answers to these questions, don’t use that source of manure, hay, grass clippings, straw or compost on sensitive crops. You can test the material by gathering several samples of the product, mix with a commercial potting soil, place in pots and plant bean seeds in the pot to see if any problems occur. Have a control sample by planting beans in a pot containing only the potting soil. If the plant sprouts and grows normally, then you will know that the product is safe to use on sensitive crops. If not, don’t use on these crops.

Animal manure is a great source of nutrients and organic matter. However, as a good home gardener, you must be aware of the sources of materials you are using and use care in their application.

Resources:

http://www.manurematters.co.uk/
http://www.extension.umn.edu/distribution/livestocksystems/M1197.html
http://www.tilthproducers.org/tpqpdfs/108.pdf
http://www.tilthproducers.org/tpqpdfs/60.pdf
http://www.puyallup.wsu.edu/soilmgmt/CopyrGarden.htm

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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.