I now understand that these two pesticides (clopyralid and picloram) can:

pass through an animal

exist for several years (sometimes decades) in manure, compost and soil

can be found on grass hay, wheat straw, oat straw and barley straw

will continue to exist through the composting process

Picloram has a half life of seventeen years, but can be eliminated through UV rays (sunshine).

Clopyralid has a half life of 11 months and legumes are especially sensitive to it.

Laboratory testing runs about $200 to $400 per test.

A home-made test involving growing peas in pots with mixtures of potting soil can be indicative.

Anybody else have known data about these two herbicides and how to avoid them?

One thing I would like to know: Suppose a farmer used either of these on his wheat field one year. The wheat straw has it on it. The next year he grows oats on the same field, but sprays no herbicides. Does the oat straw have it in it?

Another way to ask the same question: The farmer grows grass hay and sprays one of these herbicides the first year. Does the hay from the second year contain the herbicides?

Anybody else have any other info to add on these two herbicides?

-- Paul Wheaton (paul@javaranch.com), April 10, 2002

Answers

Apparently Washington State Univ. has done some extensive research into this problem, has a place to get questions answered, suggest that you contact them.

Found this and it may be of help to you: Picloram, in the pyridine family of compounds, is a systemic herbicide used for control of woody plants and a wide range of broad-leaved weeds. Breakdown in soil and groundwater: Picloram is moderately to highly persistent in the soil environment, with reported field half-lives from 20 to 300 days and an estimated average of 90 days [11]. Photodegradation is significant only on the soil surface and volatilization is practically nil [58]. Degradation by microorganisms is mainly aerobic, and dependent upon application rates [58]. Increasing soil organic matter increases the sorption of picloram and increases the soil residence time [58]. Picloram is poorly bound to soils, although it is bound better by soils with higher proportions of soil organic matter [11]. It is soluble in water, and therefore may be mobile [1]. These properties, combined with its persistence, mean it may pose a risk of groundwater contamination. Picloram has been detected in the groundwater of eleven states at concentrations ranging from 0.01 ug/L to 49 ug/L [9].

Breakdown in vegetation: Picloram is readily absorbed by plant roots, less so by the foliage, and is readily translocated throughout plants. It remains stable and intact in plants [58].

Washington State Univ., http://css.wsu.edu/compost/compost.htm Clopyralid in Compost a new site from the soil management group at WSU-Puyallup. Includes links to: Question and answers for gardeners and farmers in western Washington, a research summary on clopyralid study with turf - Dissipation in Turfgrass Clippings: Effects of Formulation and Clipping Management, and photos of clopyralid-damaged plants. 1/15/02.

Charcoal can be broadcast applied and tilled into the entire garden or used in specific areas such as mixing into the planting hole for tomatoes. Test results have shown that charcoal is an effective method for reducing the damage from picloram, although it may not completely eliminate the damage if the level of contamination is high.

-- BC (desertdweller44@yahoo.com), April 10, 2002.

Thanks for posting this Paul, I had heard bits about this but didnt realize what a problem it was. Very scary to think the hay I feed my goats could contaminate my soil for years!

-- kathy h (ckhart55@earthlink.net), April 10, 2002.