The Big Sandy Mountaineer -

New Montguide for Gardeners is available at the Extension Office

A new Montguide (MT201612AG) is available at the Chouteau County Extension office or on-line at orderpubs@montana.edu. The Montguide is titled “How to Prevent Non-Target Injury of Broadleaf Crops and Vegetables by Residual Herbicides”. The Montguide was written by Katrina Mendrey at Ravalli County Extension and Noelle Orloff (Associate Extension Weed Specialist). Segments of the Montguide are included in this article.

In 2016 the Schutter Diagnostic Lab received 17 vegetable samples with symptoms consistent with herbicide carryover from contaminated amendments like compost, manure, hay, or grass clippings. Residual herbicides can present a long-term problem for growers of broadleaf plants. Residual herbicides include aminopyralid (Milestone), clopyralid (Stinger), and picloram (Tordon). These herbicides are in a class known as plant growth regulators (PGRs). In Montana, PGRs are labeled for weed control on pasture, rangeland, roadsides, hay, cereal crops, and turf.

When plant material treated with PGRs, resulting manures, or composts produced from these materials are used as soil amendments they can injure non-target broadleaf plants. Topsoil containing residues from these herbicides can also be a source of contamination. Labels on PGRs are designed to prevent such contamination by specifying proper use of both the herbicides and end-products. It is important for herbicide applicators and vegetable growers to understand that applying soil amendments contaminated with PGR herbicides to susceptible plants can have the same effect as applying the herbicide to them.

Symptoms of PGR injury include upward cupped leaves, fringed or frilled leaf margins, distorted growth at growing points, and in extreme cases poor seedling emergence and plant death. Other factors can create similar symptoms including insect damage, drought, excess water, extreme temperature fluctuations, and ammonia toxicity. Call in to your local Extension office to determine if herbicide carryover may have been a factor in plant symptoms.

Montana State University, U.S. Department of Agriculture and Montana Counties Cooperating. MSU Extension is an equal opportunity/affirmative action provider of educational outreach.