Vegetation Management

Vegetation management for U.S. Applicators' purposes can be defined as the use of mechanical, chemical (herbicide) and other techniques to ensure the safe and reliable operation of utilities, agricultural operations, wildlife habitat, forestland, etc. These practices are used to encourage the growth of healthy vegetation beneficial to the particular site. Where chemical controls are used all applications are done in accordance with the Environmental Protection and Enhancement Act and with the environment and all its parts as primary concern.

Herbicide safety and toxicity 

Unfortunately, I hear herbicides commonly referred to as "poisons." The implication is that they pose as an extreme hazard to the environment, much in the way of long-lasting pesticides. General toxicity to fish and wildlife is expressed as LC50 or LD50.

  LC50 is the lethal concentration of a chemical in air or water that kills 50% of the test organisms in specific conditions.

  LD50 is the dose of a chemical that kills 50% of the organisms in specific test conditions. It is expressed in weight of the chemical per unit of body weight and the toxicant may be fed (oral LD50), applied to the skin (dermal LD50), or administered in the form of vapors (inhalation LD50).

  LC50 levels have been established for fish and wildlife and examples are presented in Table 3. Values there, serve as a base for ecotoxicity. Acute oral LD50 values presented in Table 3 are commonly >5000 mg/kg. In comparison, the acute oral LD50 for aspirin is 1,240 mg/kg and for table salt is 3,320 mg/kg. This means that under test conditions, acute doses of aspirin or table salt are more lethal than acute doses of the forest herbicides called amino acid inhibitors. 

Chronic ingestation of commonly used herbicides seems to pose limited health risk for malformations in the embryo or fetus, as reproductive toxins, or inducers of tumors (Table 3). These data do not justify unsafe use practices. Instead, they provide a minimum justification for continued product use in conjunction with accepted safety standards.

   Parameters such as acute and chronic toxicity, combined with product solubility, persistence (Half-Life) and agents of degradation can be used to indicate potential hazards, and when combined with common sense, help users apply herbicides safely. Users and workers need a simple, prominently displayed assessment of overall herbicide safety.

   The EPA assesses each product for safety and uses a one-word system to rate herbicide safety. The signal word - Caution, Warning and Danger - is the EPA's rating of overall product safety and it is clearly displayed on the product label. "Caution" is the lowest risk to health while "Danger" is the highest risk. Additional safety information is provided on product material safety data sheets (MSDS). Copies of MSDS may be acquired from a distributor, company representative, consultant or the web at Crop Data Management Systems, Inc. (Acrobat Reader needed). Additional information on toxicology and the fate of herbicides in the environment and in plants can be found in Ahrens (1994).

Contributed by Dr. Jimmie Yeiser, T.L.L. Temple Chair,

Arthur Temple College of Forestry and Agriculture, Stephen F. Austin State University

Adapted from a two-part series originally published in The Monitor, Fall 2000 and Spring 2001.

http://www.fri.sfasu.edu/index.php?option=com_content&view=article&id=60:herbicide