Cutting Interval and Irrigation Timing in Alfalfa: Yellow Foxtail Invasion and Economic Analysis

Yellow foxtail ( Setaria glauca (L.) Beauv.) is the most serious summer annual weed in alfalfa ( Medicago sativa L.) in the Central Valley of California. The experiment evaluated the importance of cutting interval and timing of irrigation on invasion of the weed into established alfalfa. The crop was cut on a 25‐, 31‐ or 37‐d interval. Irrigation was applied on the same day as cutting or after a delay of 7 or 14 d. A factorial treatment combination was used in a randomized complete block fielld design. The experiment was continued for 3 yr. Alfalfa yield increased with increased length of cutting interval but was not affected by irrigation regime. Yellow foxtail invasion was minimal at the 37‐d cutting interval, was intermediate at the 31‐d interval, and reached 20 to 30% of late‐season harvests at the 25‐d cutting interval. Delaying irrigation following cutting reduced yellow foxtail invasion 2 yr out of three; this effect was largest for hay cut on the 31‐d interval. Cash‐flow economic analyses showed that cutting at a 25‐d interval resulted in the lowest net return due to low overall yield and substantial yellow foxtail invasion late in the season. Hay cut at the 31‐d cutting interval would provide the highest net return. Reduced alfalfa quality compromised the return for the 37‐d cutting interval. Yellow foxtail can be controlled in alfalfa by manipulation of cutting interval.