Herbicides Forest

U.S. Department of Agriculture, Pesticide Background Statements, Vol. I, Herbicides, Forest Service, U.S. Department of Agriculture, Agriculture Handbook No. 663, 1984. 

H Br Effective non 776 selective herbicide in controlling weeds in orchards and forests ... 

S.R. Shewchuk, K. Wallace, and J. Maybank, An Evaluation of the Rotorod Sampler for a Forest Herbicide Drift Monitoring Program, SRC Publications, E-2310-2-E-90, Saskatoon Research Center, Saskatoon, Canada, p. 19 (1991). 

Rapid growth of chemical weed control did not occur until after World War II when a herbicide was introduced by Jones in 1945 at the Imperial Chemical Industries of England 2,4-dichlorophenoxyacetic acid (2,4-D). Its utility has come from its ability to kill selectively broadleaf weeds in cereal grains, com, and cotton. It does not disturb the soil and is not persistent. 2,4,5-T was launched commercially by American Chemical Paint Co. in 1948 (now Union Carbide) to combat brush and weeds in forests, along highways and railroad tracks, in pastures, and on rice, wheat, and sugarcane. 

The production of compounds which may act as allelochemicals is not restricted to higher plants. For example, Heisey, DeFrank and Putnam (41) have discussed substances produced by soil microorganisms which may have herbicidal activity. Bacteria may also mediate allelopathic activity in economically important situations such as forest regeneration (Line, personal communication) crop/weed associations ( ), and reduced cultivation systems where plant residues are retained ( ). 

Dioxins are sometimes—but rarely—produced in nature, most commonly during volcanic eruptions and forest fires. Their most common source in the environment are industrial reactions in which they occur as by-products of other chemical changes or during the incineration of certain synthetic organic compounds. For example, trace amounts of 2,3,7,8-TCDD occur as an impurity in the herbicide Agent Orange (a mixture of 2,4,5-trichlorophenoxyacetic acid [2,4,5-T] and 2,4-dichlorophenoxyacetic acid [2,4-D]), which was... 

In an attempt to obtain a fairly good nation-wide picture of the present practices in regard to weed control in forest nurseries and methods of application of the herbicides, the author wrote to some 20 nurserymen and investigators, representing major geographic regions of the United States. The results of the survey are reported below. 

There are a number of mechanisms of selectivity that are found in the herbicides that are used today. Diuron is used as a residual broad-spectrum herbicide in a number of situations such as plantations and forests. It is, however, phytotoxic to most perennial species and the selectivity shown by the established trees is because the compound does not move within the soil profile to a depth where established tree roots will absorb the compound in sufficiently high concentrations to exert an effect. This is selectivity by placement. 

Thompson, D.G. and Stephenson, G.R. (1999) Effects of seven forestry management herbicides on Myriophyllum sibiricum, as compared with other nontarget aquatic organisms. Can J Forest Res Rev Can Rech Forest, 29, 1158-1169. 

The spatial distribution of pesticides in streams coincides with the types and intensity of land uses in basins. Many herbicides, such as atrazine, are used exclusively or predominantly on row crops, while other pesticides, such as the herbicide prometon and the insecticide diazinon, are usually used in urban areas. Atrazine concentrations were higher in the row-crop basins than in the urban or pasture/forest basins. Diazinon concentrations were higher in the urban basins than in the row-crop or pasture/forest areas. 

T excreted by the 21 forest workers in two exposures under typical field conditions. The highest dose was received by mixers who handled the herbicide concentrate, followed by applicators using backpack sprayers, spray tractor drivers, helicopter... 

Development of weed resistance to triazine herbicides has necessitated alternative weed control strategies. Rotation of triazines with other herbicides and combining triazines with other chemistries has been effective in ornamentals and Christmas tree plantations (Van Himme, 1989). Supplemental treatments in Christmas trees have been effective, using directed sprays of phenoxy herbicides or glyphosate before resistant weeds mature and produce seeds. Weed resistance from triazines is not a problem in most forest settings where the herbicide is applied only once or twice in a rotation, since 1 or 2 years of herbaceous weed control normally ensures survival and eventual dominance by conifers. When the conifer canopy closes, virtually all herbaceous vegetation is shaded out for some decades hence resistant weeds, if present, fail to survive from one generation to the next. 

Role of Triazine Herbicides in Production of Forest Conifers 231... 

Triazine herbicides are primarily effective in controlling herbaceous weeds. A notable exception is the use of granular hexazinone for controlling woody invaders such as oaks (Quercus spp.) or aspen (Populus tremuloides) in conifer stands on medium- and fine-textured soils in the South or in boreal forests. Hexazinone also is used in the Maritime Provinces of Canada for controlling woody and herbaceous growth in natural Christmas tree stands (Townsend, 1995a). The impact of herbaceous plant cover is somewhat different from that of woody plant competitors, so control strategies on various forest conifer sites may differ. 

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