Yuma County Office
2200 W. 28^th Street, Ste. 102
Yuma, AZ 85364
(928) 726-3904
(928) 726-8472 FAX

Production Update:
Cutting height: The optimum cutting height for alfalfa varies from about 2 to 4 inches. As cutting height is increased, more growth occurs from buds originating on the stems and less from the crown. Stem buds are less productive than crown buds, so increasing cutting height often reduces yields. However, crown bud development is suppressed if alfalfa is cut at early stages of growth or on a frequent basis. In these cases, lack of crown bud development can be compensated for somewhat by increasing the cutting height and encouraging more regrowth from the stems. A cutting height of 3 inches resulted in prolonged stand life compared to a 1 inch cutting height in an Arizona study. Crop quality can be manipulated with cutting height since the lower part of the plant is poorer in quality than the top.

Insect Management: Alfalfa caterpillar, Colias eurytheme ( picture, larvae), also known as alfalfa butterfly, is a warm weather pest of alfalfa. There can be as many as seven generations between May and October, in the low desert. Start checking fields for alfalfa caterpillars when yellow alfalfa butterflies first appear in May. When alfalfa butterflies are seen flying over tall alfalfa, they most likely emerged from that field. Eggs are laid singly, standing on end, on the upper surface of leaves in fields with re-growth under 6 inches. Larvae hatch in 3 to 10 days, grow to about an inch long and pupate in approximately two weeks. Alfalfa caterpillars are green with white stripes down their sides and are distinguished from beet armyworm ( picture, larvae) by their velvety appearance. Monitor fields weekly from June through October, checking 2 to 3 times per week during periods of heavy infestations. Take 5 sweep counts in 4 to 5 field locations. Check worms for parasitism by pulling heads off an alfalfa caterpillar larva, squeeze out the body contents, and look for an Apanteles wasp larva. Treat when field counts average 10 non-parasitized caterpillars per sweep.

Weed Control: It is well worth the effort to shut the sprayer off for a few randomly spaced spots in the field to see how much good a herbicide has worked. When weed infestations are heavy, even 70 or 80 percent control can look like no control without an untreated check. Growers worried about leaving weeds in the field can come back and spray them before they have gone to seed.

10 Year Summary (April 22, to May 5, 1994-2003):

Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

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