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ARS Home » Southeast Area » Stuttgart, Arkansas » Harry K. Dupree Stuttgart National Aquaculture Research Cntr » Research » Publications at this Location » Publication #149580
Title: EFFECTS OF DIURON AND OTHER AERIALLY-APPLIED COTTON HERBICIDES AND DEFOLIANTS ON THE PLANKTON COMMUNITIES OF AQUACULTURE PONDS

Author
item PERSCHBACHER, PETER - UAPB
item Ludwig, Gerald

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2003
Publication Date: 2/5/2004
Citation: Perschbacher, P., Ludwig, G.M. 2004. Effects of diuron and other aerially-applied cotton herbicides and defoliants on the plankton communities of aquaculture ponds. Aquaculture. 233:197-203.

Interpretive Summary: Aquaculture ponds are often located near cotton fields. Cotton cultivation usually requires the use of herbicides and defoliants to prevent invasion of weeds and to prepare the crop for harvest. Crop-dusting airplanes often apply the herbicides and defoliants and the spray frequently drifts due to wind currents. If the drifting spray reaches the aquaculture ponds it may have an adverse effect on plankton populations in the ponds and subsequently the fish or other aquaculture product being grown may also be damaged. This study determined the individual effects of diuron as an herbicide, paraquat, quizalofop, dimethipin, diuron as a defoliant, ethephon, tribufos, and sodium chlorate on phytoplankton and zooplankton communities and critical water quality properties in mesocosms filled with water from aquaculture ponds. Concentrations of chemicals tested included the equivalent of a direct over-spray, and one-tenth, and one-hundredth of that amount. Effects were measured at 24 and 48 hours after application and compared to a control that had not been exposed to the chemical. If an effect were found additional sampling was conducted. Except for the diuron compounds, the cotton herbicides and defoliants produced no measurable impacts on pond plankton or associated water quality. Diuron, used as an herbicide, depressed phytoplankton levels and reduced photosynthesis and dissolved oxygen levels significantly. Copepods, a zooplankton group were also reduced in concentration. Recovery was slow. Three weeks after application phytoplankton chlorophyll a levels were still only a third of untreated water. Even when diuron was used at one tenth the strength as a defoliant it adversely affected pond plankton.

Technical Abstract: Seven, aerially-applied cotton herbicides and defoliants were tested for possible adverse impacts on pond phytoplankton and zooplankton and critical water quality variables. Treatments simulated direct spraying of ponds and high and low amounts of drift judged able to reach the pond, 1/10 and 1/100 direct rates respectively. The study was conducted in 12, 500-l outdoor pool mesocosms, filled with pond water from an adjacent goldfish brood pond. Plankton and water quality samples were taken just prior to application and at 24 h and 48 h after application. Sampling for chemicals showing effects were continued approximately weekly until treatments returned to no significant difference from control. Chemicals tested and direct rates (kg active ingredient ha-1) were diuron as herbicide (1.4), paraquat (0.83), quizalofop (0.05), dimethipin (0.15), diuron as defoliant (0.1675), ethephon (0.176), tribufos (0.99) and sodium chlorate(5.28). Except for the diuron compounds, the cotton herbicides and defoliants produced no measurable impacts on pond plankton or associated water quality. Following application on March 5 of diuron, used as an herbicide, chlorophyll a levels and photosynthesis were significantly depressed in relation to treatment. Recovery occurred slowly, and by week 3 chlorophyll a levels at the high drift dosage had returned to 1/3 the control. Copepod adult and nauplii zooplankton levels were depressed at week 2. Fall application of diuron, as a defoliant at 1/10 the spring rate, produced similar effects when compared by concentration.