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KC Permaculture Extension Bulletin # M100 February 2016 Author: Steve Mann

Herbicide Carryover in Straw, Manure and Compost

You may be getting more than you bargained for in your straw, compost or manure ifthe crops they were derived from were treated with persistent herbicides (Table 1).

These herbicides can persist on vegetation such as straw, in the soil and even in the

manure of animals who ingested crops and grasses treated with these chemicals for

many years.

A class of herbicides formulated from pyridine carboxylic acids such as Clopyra ,

Aminopyralid, Aminocyclopyrachlor and Picloram, all manufactured by Dow

AgroSciences, are the main culprits.

Table 1. Some herbicides containing picloram, clopyralid, and aminopyralid.Source: North Carolina Cooperative Extension

Organic straw and manure from animals on certified organic farm should be free of thisdeath-a cide. Its important to ask the sources of your materials if they used any of

these chemicals.

Symptoms reported by growers include poor seed germination reduced yields;seedling death; reduced yields; twisted, cupped, and elongated leaves and misshapenfruit. Species most affected are listed in Table 2.

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KC Permaculture Extension Bulletin # M100 February 2016 Author: Steve Mann

Table 2. Some plants affected by picolinic acid based herbicides.Source: North Carolina Cooperative Extension

If you suspect your material might be contaminated, you can do a simple test forpersistent herbicides. A pot bioassay involves growing beans, peas, or tomatoes in thesoil, manure, compost or straw that you suspect is contaminated.

Gather 6 -10, 1 qt random samples of the material and thoroughly mix together.Prepare a sample by mixing one part of the mixed test material with one partcommercial growing mix. Place in 4 pots and plant 3 -4 seeds in each. Two controlpots should be filled with only the commercial potting mix and planted with the sameseed. If you are testing straw, thoroughly chop up straw and mix one part straw to fourparts growing mix then fill and plant test pots . Be sure to label each test pot and keeprecords of planting dates and species being tested.

Two to three weeks after germination there should be two to three sets of true leavesgrowing. If the control pots have normal looking plants and the test plants aremisshapen and stunted then it is highly likely the material is contaminated.

These herbicides eventually break down through exposure to sunlight, soil microbes,heat, and moisture. Herbicides can be deactivated in as few as 30 days depending onthe conditions but deactivation and breakdown can take several years. Hay has been

reported to have residual herbicide activity after three years storage in dry, darkbarns. Degradation is particularly slow in piles of manure and compost.

Solarization of contaminated fields and piles is a possible method of hasteningbreakdown. Specially designed compost teas and mycoremediation with inoculatedwoodchips are also possible methods for mass decontamination.

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KC Permaculture Extension Bulletin # M100 February 2016 Author: Steve Mann

References:

CDMS Agro-chemical database with access to all the herbicide labels:http://www.cdms.net/Label-Database

Davis, J., Johnson, S. E. , Jennings, K. and Yelverton, F. 2014. HERBICIDE CARRYOVERIN HAY, MANURE, COMPOST, AND GRASS CLIPPINGS. North Carolina CooperativeExtension.

US Composting Council 2015. Persistent Herbicide FAQ. Alailable online at:http://www.cdms.net/; last accessed February 7, 2016.

http://www.cdms.net/Label-Databasehttp://www.cdms.net/Label-Databasehttp://www.cdms.net/http://www.cdms.net/http://www.cdms.net/http://www.cdms.net/Label-Database