| Abstract/Contents: | "Inclusion of nitrogen-fixing legumes is a proposed means of increasing the sustainability of certain turf scenarios. However, little is known about managing for legumes within maintained turf. Noxious weed succession is problematic during the establishment of mixed turf-legume swards. Selective weed control within mixed swards proves challenging, often because of legume susceptibility to herbicide injury. Clovers (Trifolium spp.) are common turf "weeds" throughout the United States and are likely large net contributors to nitrogen fertilization within poor soils. For these reasons, our objectives were to identify herbicides that are safe on clovers and turf as well as describe their effects upon important phenological characteristics of clover stands. Research was conducted in Auburn, AL on naturalized stands of three clover species, including: white clover (T. repens), ball clover (T. nigrescens), and small hop clover (T. dubium). Herbicide treatments were applied March 1, 2011 via a CO2 pressurized back-pack sprayer at 280 L Ha-1 utilizing Tee-Jet 8002 nozzles. Studies were randomized complete blocks by design (4 blocks) and were repeated at two locations per species. Treatments included a non-treated control and fourteen herbicides: 2,4-D amine (15.8 g ae 100 m-2), 2,4-DB amine (15.8 g ae 100 m-2), clopyralid (4.2 g ae 100 m-2), imazaquin (5.6 g ai 100 m-2), imazethapyr (0.7 g ai 100 m-2), imazamox (0.5 g ai 100 m-2), glyphosate (11.2 g ai 100 m-2), halosulfuron-methyl (0.5 g ai 100 m-2), metsulfuron-methyl (8.4 g ai 100 m-2), nicosulfuron (0.3 g ai 100 m-2), pronamide (2.8 g ai 100 m-2), simazine (11.2 g ai 100 m-2), bentazon (8.4 g ai 100 m-2), and metribuzin (4.2 g ai 100 m-2). Flower- and trifoliate leaf- density, as well as clover stand height, were measured 4 WAT, during flower senescence, and are presented as reduction relative to the non-treated. Clover injury was visually assessed relative to a non-treated check 1, 2, 4, and 6 weeks after treatment (WAT). We discuss 6 WAT assessments, as they are indicative of the long-term control expected from these herbicides. Basic normality assumptions were confirmed within SAS procedure MIXED. Species response did not differ due to location; therefore, herbicide main-effects were separated by LSD (α = 0.05), and results are presented for each species. White clover was uninjured by bentazon, simazine, imazamox, imazethapyr, halosulfuron, pronamide, and 2,4-DB when assessed 6 WAT. Like that of previous research, 2,4-D and metribuzin injury to white clover was acceptably low (< 35%). However, nicosulfuron, imazaquin, glyphosate, clopyralid, and metsulfuron injured white clover greater than 65%. When assessed 4 WAT, trifoliate leaf-densities and stand-heights were similarly affected by herbicides. An interesting observation was that 2,4-D and 2,4-DB equally reduced leaf-density (18%), but of the two, only 2,4-D reduced clover height. White clover flower-density was highly variable, though 2,4-D, glyphosate, clopyralid, and metsulfuron clearly reduced flower-density to zero. Ball clover was uninjured by bentazon, pronamide, and 2,4-DB when assessed 6 WAT. Imazamox and simazine injury was less than 25%, while 2,4-D and imazethapyr injury was less than 45%. All other treatments injured ball clover greater than 77%. Trifoliate leaf-densities and clover heights generally confirm visual assessments. Only pronamide and imazamox did not affect leaf-density, while 2,4-DB, bentazon, simazine, 2,4-D, and imazethapyr reduced leaf-density less than 41%. Unlike previous greenhouse experiments, metribuzin was highly injurious to ball clover, with nearly 90% reduction in trifoliate leaf-density and greater than 75% reduction in clover height. Ball clover height was unaffected by pronamide and 2,4-DB but actually increased due to treatment with bentazon and simazine. Similar increases in plant vigor have been reported due to other photosystem-II inhibiting herbicides. Flower-densities were not affected by 2,4-DB or bentazon but were slightly reduced (< 50%) by pronamide and simazine. All other treatments reduced flower-density by greater than 79%. Hop clover was uninjured by bentazon, pronamide, imazethapyr, and 2,4-DB when assessed 6 WAT. Imazamox injury was less than 30%, while nicosulfuron injury was 50%. All other treatments injured hop clover greater than 80%. Pronamide, simazine, bentazon, and imazethapyr did not reduce clover height. Pronamide, simazine, imazamox, and imazethapyr did not reduce hop clover leaf-density, while other herbicides reduced leaf-density greater than 40%. These results demonstrate a range of herbicides tolerated by Trifolium species. They include pronamide, 2,4-DB, bentazon, simazine, imazamox and imazethapyr. They also demonstrate a range of effects upon phenological responses, such as height, flowering, and leaf characteristics. Future research must determine the effects of application timing as well as define injury to other important amenity turf-legumes." |
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