Nutsedge (cyperus Spp) Control in Alfalfa

The competitive advantage of purple and yellow nutsedge in low desert alfalfa production areas of Southern California and Arizona is due to a combination of factors. These include frequent harvest and irrigation, high incident solar radiation, high summer temperatures that are supraoptimal for alfalfa growth, and the presence of C4 photosynthesis and vegetative reproduction (e.g., tubers) in nutsedge species. Research in Arizona has shown that only three herbicides have the ability to suppress the growth of purple nutsedge in alfalfa in the low desert: Eptam (EPTC), Zorial (norflurazon) and glyphosate (Roundup, Touchdown and other trade names). Multiple Eptam granule applications can reduce the amount of nutsedge foliage in alfalfa hay and the density of purple nutsedge shoots (stem/ft) compared to untreated areas but nutsedge density in both treated and untreated areas increased during the first two years of the alfalfa stand. Zorial granules applied at 1 to 3 lb ai/A in a heavily infested alfalfa field (60 to 80% nutsedge cover) resulted in poor control (30 to 40% control) following a single spring application and 76 to 94% control in treatments receiving two applications per year (i.e., spring and summer) for 2 years. Zorial was not applied in the third year of the study but residual soil concentrations of norflurazon continued to provide substantial suppression of purple nutsedge. By August of the third year, the 2 lb ai/A per year and lower rate treatments did not keep purple nutsedge densities from rebounding to pretreatment levels while the 3 and 4 lb ai/A per year rate provided 51 and 75% suppression, respectively. Similar purple nutsedge suppression was observed in a second study where treatments were initiated in the spring following a fall alfalfa planting in a field with a lower initial density. In another study, glyphosate was applied in the summer and fall in a fallow field infested with purple nutsedge that mimicked the appearance of heavily infested, recently cut and irrigated fields in Parker Valley, AZ. Two to 4 glyphosate applications at 1.5 lb ae/A greatly reduced nutsedge tuber sprouting and shoot emergence in the following spring. Experiments to date suggest that reducing purple nutsedge tuber populations in alfalfa fields may be greatly facilitated by the commercial introduction of Roundup Ready alfalfa.