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Title: Dissipation of Clomazone, Imazapyr and Imazapic Herbicides in Paddy Water under Two Rice Flood Management Regimes

item SCHREIBER, FABIO - Federal University Of Pelotas
item SCHERNER, ANANDA - Aarhus University
item Massey, Joseph
item ZANELLAY, RENATO - Universidade Federal De Santa Maria
item AVILA, LUIS - Federal University Of Pelotas

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2017
Publication Date: 3/1/2017
Publication URL:
Citation: Schreiber, F., Scherner, A., Massey, J., Zanellay, R., Avila, L. 2017. Dissipation of clomazone, imazapyr and imazapic herbicides in paddy water under two rice flood management regimes. Weed Technology. 31 (2):330-340.

Interpretive Summary: Intermittent rice flooding, where floodwaters are allowed to subside to mud before resuming irrigation, reduces irrigation use by up to 50% over conventional flooding methods. Rice herbicides are tested under continuous flooding. This study was conducted to determine if intermittent flooding, also known as alternate wetting and drying, changes the persistence of three common rice herbicides in rice fields. If intermittent flooding changes the dissipation rates of the herbicides this could alter weed control and/or environmental profile of the herbicides. The study found that for two of three herbicides tested, dissipation rates were slower under intermittent versus continuous flooding while the dissipation rate of the third herbicide was unaffected by flooding regime. These data suggest that testing of herbicides under conditions of intermittent flooding, used to reduce water use in rice production, may be required as agriculture strives to grow more food with less water while maintaining yields and minimizing environmental impacts.

Technical Abstract: Pesticides are frequently detected in rivers, lakes and groundwater sources in regions where rice is cultivated in Brazil. The transport of these compounds to water sources is strongly related to the irrigation system adopted in paddy fields. However, information on the dissipation of clomazone, imazapyr and imazapic in paddy water under different irrigation system is not available in the literature. The objective of this study was to investigate the effect of two irrigation systems (intermittent (IF) and continuous (CF) flood) on the dissipation of clomazone, imazapyr and imazapic in paddy water in two sowing dates. RESULTS: The single first-order model provided the best fit to describe the dissipation of all herbicides across the irrigation treatments. Imazapic was the least persistent herbicide in paddy water, with DT50-values of ca. 3 and 5 days under CF and IF, respectively. Imazapyr required a twofold increase in time to reach its half-life in water in contrast to imazapic, with DT50-values of ca. 6 and 11 days under CF and IF, respectively. Clomazone showed the highest DT50-values, varying between 7-21 days under CF and IF respectively. CONCLUSION: Imazapyr and imazapic dissipation was faster under CF, while clomazone was not affected. Sowing date did not significantly affect the dissipation of imazapic or imazapyr but clomazone dissipation was nearly twice as fast in the second sowing date. The manipulation of irrigation management may provide a means to reduce the negative effects of rice production on susceptible water bodies.