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Project description

Sheep Grazing as a Weed Control Practice for Seedling Alfalfa in the Lower Colorado Desert. (90CC068)
Program UC IPM competitive research grants program
C.E. Bell, Cooperative Extension, Imperial County
J.N. Guerrero, Cooperative Extension, Imperial County
Host/habitat Alfalfa
Pest Unspecified Weeds
Disciplines Animal Sciences, Weed Science
Cultural Controls
Start year (duration)  1990 (Two Years)
Objectives Compare sheep grazing to herbicides and mowing as weed control methods in seedling alfalfa.

Determine the long-term effect of these weed control methods on alfalfa stand, yield, and quality.

Determine the feed value of common winter annual weeds in the Imperial Valley.

Final report The goal of this research project was to compare sheep grazing as a weed control practice to the use of herbicides or the practice of mowing. Over the three year project (funded two years by IPM), we found that sheep grazing could control weeds nearly as well as herbicide use, depending upon several factors. One important factor is weather; rain in two of the three years prevented the sheep from grazing the field as thoroughly as we would have liked for maximum weed control. Conversely, in two of the years the herbicide treatment (2,4-DB in particular) caused significant crop yield reduction.

The long-term impact of weeds and weed control method in seedling alfalfa is negligible. At the second cutting, after grazing or mowing, weeds were not very abundant regardless of treatment. Treatment did have an effect on crop yield, with the herbicide-treated plots having the highest yields. At the third harvest, there were few to no weeds and crop yields were not very different between treatments. At the fourth and all subsequent harvests, there were no differences between treatments for yield, quality, and stand (crop density).

The feed value of the weeds in this trial varied considerably between species. In general, most were comparable to alfalfa, some were better. Sheep showed a feeding preference toward the weeds in the plots, particularly London rocket and volunteer wheat, leaving alfalfa to be eaten last.

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