Early spring clipping and herbicide treatments delay alfalfa maturity

Delays in harvesting first-crop alfalfa (Medicago sativa L.) at recommended maturities for optimum forage quality are caused by untimely rainfall and the logistics of harvesting large acreages. Our objective was to determine the effect of spring preharvest clipping and herbicide defoliation treatments on first harvest maturity and leaf:stem ratio (L:S), on first harvest and total season forage yield and forage quality, and on total season returns over costs. A 2-yr field study was conducted at Grand Rapids, MN, on a Cowhorn very fine sand (Aeric Haplaquepts, coarse-loamy, mixed, nonacid). Spring defoliation treatments consisted of clipping to a 3 in. stubble height when alfalfa was 6 or 9 in. tall and application of MCPA amine at low (average of 0.16 lb a.i./acre) and high (average of 0.23 lb a.i./acre) rates when alfalfa was at a 6 in. height. An untreated control was harvested at bud stage (about 10 June) and a set of defoliation treatments along with untreated controls were each harvested 1 and 2 wk after the bud harvest. Spring clipping and herbicide treatments consistently delayed alfalfa maturity and enhanced alfalfa leafiness compared with untreated controls harvested the same day and often resulted in similar maturity as a control treatment harvested 1 or 2 wk earlier. Spring clipping at a 9 in. height or application of a high rate of herbicide delayed maturity compared with clipping at a 6 in. height. All spring clipping and herbicide defoliation treatments reduced first and total season yields compared with controls harvested the same date and resulted in yields equal to or less than a control harvested 1 or 2 wk earlier. Yield reduction was usually less for the 6 in. clipping or the low herbicide rate. Forage crude protein (CP) and fiber concentration of clipping and herbicide treatments was similar to those of an early control harvested 1 wk earlier, but only clipping at a 9 in. height and use of a high herbicide rate maintained forage quality for 2 wk. Total nonstructural carbohydrates (TNC) and residual yields taken the following spring were not affected by spring treatments. Spring defoliation often resulted in less net return than the controls due to reductions in yields and added costs of applying treatments, but it may still be a useful practice for producers with large acreages who wish to minimize the risk of rain damage.