Author
 |
Ludwig, Gerald |
|
Submitted to: Catfish Farmers of America Annual Meeting
Publication Type: Abstract Only Publication Acceptance Date: 4/27/2003 Publication Date: 4/27/2003 Citation: LUDWIG, G.M. AERIALLY APPLIED COTTON HERBICIDES-THEIR EFFECT ON FISH PONDS.. CATFISH FARMERS OF AMERICA ANNUAL MEETING. 2003. p.47. Interpretive Summary: Technical Abstract: Two aerially-applied cotton herbicides containing diuron were tested along with six others for possible adverse impacts from drift on fish pond plankton and water quality. Four treatments in triplicate 145-gallon outdoor tank mesocosms filled with fish pond water evaluated 1) simulated overspraying (100% field rate), 2) low level drift (1% of full field rates), 3) high level drift (10% of the full rate), and 4) no spraying (control). Herbicides were evaluated at the approximate dates of field application. Herbicide (without additives) was sprayed on the tank surface and plankton and water quality evaluations conducted at 24 and 48 h post application. If effects were noted, selective evaluations were continued until systems returned to normal. Of the eight herbicides tested only those containing diuron significantly affected water quality and plankton. Other herbicides tested were paraquat and quizalofop, and dimethipin, tribufos, ethephon and sodium chlorate as defoliants. Diuron (Direx) is applied in the spring as a burn-down. The full rate was equivalent to 0.2 ppm active ingredient concentration in the tanks. All treatments were added on March 5. As a result of the inhibition of oxygen production (by light/dark bottle) and reduced plankton levels, morning oxygen levels fell to 3 ppm at week 1 in the full and 10% treatments and slowly improved to near control levels by week 3. Positive impacts noted in the full and 10% treatments included reduced levels of geosmin/earthy off-flavor producing Anabaena beginning at week 1, with essentially complete elimination after week 3; and reduced pH levels and resulting lower UIA levels after 24 h and continuing into week 4. Numbers of adult and nauplii copepod zooplankton were reduced after week 2 and extending into week 3, presumably as a result of lowered phytoplankton levels. In the fall diuron (Ginstar) is used as a defoliant at approximately 1/10 the spring rate, equivalent to 0.02 ppm active ingredient in tanks at the full rate. The labeled rate for use in catfish ponds is 0.01 ppm per application. Following application on Sept. 23, similar effects to the spring application were only noted at the full rate. Oxygen production was halved from 24 h post application through week 1. Morning oxygen levels fell below 3.0 ppm at week 2, but returned to near control levels by week 3. Green algae were stimulated and bluegreen algae reduced. Copepod populations were reduced in the full and 1/10th strength applications of Direx during the second week of application results but returned to pretreatment levels by the end of the experiment. |
