Risk evaluation to fish ponds of drift from common aerially-applied herbicides to five major row crops of the delta

Authors: PERSCHBACHER, PETER - UAPB; Ludwig, Gerald

Submitted to: Proceeding of World Aquaculture Society
Publication Type: Abstract Only
Publication Acceptance Date: 12/10/2008
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Row crop herbicides were tested for possible adverse effects on fish production pond plankton and water quality in triplicate 500-L outdoor, pool mesocosms. Treatments were drift at low (1% of full field rates) and high levels (10% of the full rate) to production ponds of 5 ha and larger, and no drift (control). Herbicide (without additives) was sprayed on the pool surface and evaluations repeated at 24 and 48 h post- application, and if effects were noted continued until morning oxygen levels did not differ from controls (ie. recovery). Herbicides were applied to fish pond production water and algae communities at approximately the same time of year as in fields. Forty herbicides were tested, including 11 soybean, 13 rice, 10 cotton, 5 corn and 1 wheat aerially-applied herbicides. Only diuron (cotton) affected phytoplankton and oxygen production in relation to dose. However, morning oxygen levels fell to critical levels of 3 ppm and below after one week in the high drift treatment. Zooplankton were also reduced relative to control levels at both drift levels. Positive impacts noted from diuron high drift were reduced bluegreen algae and reduced unionized ammonia. Two additional herbicides, atrazine (corn) and carfentrazone (soybean) primarily affected zooplankton. Although propanil (rice) drastically reduced photosynthesis in laboratory test, in outdoor mesocosms no adverse affects were seen and enhanced chlorophyll a levels and reduced pH and bluegreen abundance were seen as positive results. Additional research focused on drift effects of propanil on different species pond production systems and on floating algae masses (scums) and propanil and atrazine on smaller fry and fingerling ponds. Greater impact was noted on midlevel algal levels (50-200 ug/l as in catfish ponds) than in low and midlevel chlorophyll a levels (below 20 and above 300 ug/l as in freshwater shrimp and goldfish ponds, respectively). Scums were more susceptible than populations mixed in the water column and impacts approximated direct application levels (ie. overspray). Smaller ponds were found to have potential drift levels of up to 3 times larger production ponds. Greater effects were found accordingly, however chlorophyll a was low and reduced the impacts. Ph and unionized ammonia was also reduced. Thus, little impact from propanil was expected on fry production.