Herbicide dissipation studies in southern forest ecosystems

Abstract

Results of research on the movement of hexazinone, imazapyr, picloram, and sulfometuron in first‐order watersheds in the southern United States are presented. Herbicides contaminate surface waters to varying degrees, depending on application rate, method of application, product formulation, and site‐specific characteristics. Highest concentrations are observed in streams in ephemeral pulses during the first three storm events after application. Streamside management zones greatly reduce the amount of herbicide entering streams from forestry applications. Soil persistence of herbicides is highly variable and a function of many site characteristics. Plant residues have been monitored and found to dissipate rapidly, with half‐lives < 40 d.

Lixiviação e persistência dos herbicidas sulfentrazone e imazapic

“…A atividade biológica e o seu movimento no solo são grandemente influenciados por numerosos fatores ambientais. Entre esses fatores, tem-se demonstrado que a textura, o tipo de argila, a umidade e o pH influenciam diretamente a adsorção e, consequentemente, a mobilidade do imazapyr no perfil do solo (Michael & Neary, 1993;Ismail & Ahmad, 1994). Wehtje et al (1987) observaram maior mobilidade do imazapyr em solos argilosos e, também, que essa mobilidade diminuiu com a redução da umidade e do pH do solo.…”

Best Management Practices for Silvicultural Chemicals and the Science Behind Them

“…The residence time of silvicultural chemicals in a given layer of soil (e.g., 0-15 cm depth) is described in terms of half-life or the time required for dissipation of half of the beginning concentration (Michael and Neary, 1993). Half-lives of some silvicultural chemicals currently in use are presented in Table III.…”

“…Overland flow occuring shortly after herbicide application potentially contains very high concentrations of herbicide which it carries to streams. Because of its short residence time prior to entry into streams, overland flow results in higher levels of stream contamination than that observed from herbicide which has leached through the soil profile and entered streams through baseflow (Michael and Neary, 1993;Michael et al, 1999;.…”

“…The results of several studies, which monitored the environmental fate of forestry herbicides used in the southern United States, have been reported (Michael and Neary, 1993). Another report (Michael, 2000) summarized surface and groundwater contamination data from reports for North America published between 1974 and 2000.…”

“…Michael and Neary (1993) have reported stream contamination from herbicide applications utilizing very conservative application technology. Both single-stem injection and soil spot treatments applied with 32.8 ft (10 m) SMZs resulted in stream contamination at levels up to approximately 0.04 mg L −1 .…”