The effect of annual spring PRE applications of fenac, metribuzin, and terbacil on the competitiveness of sugarcane with bermudagrass during a 3-yr crop cycle was evaluated. For each herbicide treatment, bermudagrass was allowed to interfere with sugarcane during the growing season for 0, 1 (plant-cane crop only), 2 (plant-cane and first-ratoon crops), or 3 (plant-cane through second-ratoon crops) yr. Predicted total yields of cane from the three harvested crops was 3600 kg ha−1 higher on average in plots maintained free of bermudagrass and treated with metribuzin than where fenac and terbacil were applied. Bermudagrass biomass increased with each growing season. Greatest biomass production occurred in the fenac plots and the smallest in terbacil plots. Bermudagrass did not reduce the predicted total yields of cane where metribuzin or terbacil was applied. With fenac, predicted total cane yields were 4, 7, and 11% lower than the weed-free control where bermudagrass interference was allowed for 1, 2, and 3 yr, respectively. Season-long bermudagrass interference in the fenac plots reduced actual cane yields 10% (plant-cane crop), 6% (first-ratoon crop), and 14% (second-ratoon crop) when compared with plots maintained free of bermudagrass for the entire growing season.

Several chemicals were evaluated in the laboratory for their ability to inhibit growth of hydrilla [Hydrilla verticillata (L.f.) Royle] from tubers. Fenac [(2,3,6-trichlorophenyl)acetic acid] and dichlobenil (2,6-dichlorobenzonitrile) were effective in controlling regrowth in outdoor aquaria. In field tests, hydrilla regrowth was controlled for over 13 months by single applications of 34 kg/ha rates of fenac and over 48 months in one of three replicates treated with 11 kg/ha dichlobenil. Regrowth occurred in controls within 2 to 6 months. There were no differences in the number of viable propagules found in hydrosoil before and 13 months after treatments. Regrowth occurred from root-stocks and from tubers. Regrowth was associated with disappearance of the herbicides from water.