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

Production Update:

Nitrogen Fixation - Temperature: Soil temperatures below 50 F and above 80 F can decrease nitrogen fixation. Soil temperatures are usually close to the mean air temperature. Many of the documented responses of alfalfa to nitrogen fertilizer have been on cold soils. Conversely, many growers worry that nitrogen fixation by alfalfa is hampered by high temperatures and fertilize alfalfa with nitrogen during the summer. Soil temperature does not fluctuate as widely as air temperature, and the temperature experienced by alfalfa nodules beneath the soil surface may be within the optimum range even on hot or cold days.

Insect Management: Cowpea aphid (picture) is a serious pest of alfalfa that can warrant treatment with an insecticide when populations are growing rapidly. Cowpea aphid is attacked by several predators (bigeyed bugs, damsel bugs, lacewings, lady beetles, and syrphid fly larvae) and parasites. Aphid parasites, Lysiphlebus sp. and Diaraetiella sp. have been reared from cowpea aphid mummies collected from both the high and low desert. Populations of sevenspotted lady beetle, Coccinella septempunctata and aphid parasites often build to levels capable of controlling cowpea aphid in alfalfa fields not sprayed with insecticides.

Weed Control: Acreage of alfalfa is higher than it has been since the 1950's. It was considered, however, only a "common rotational" crop in the University of Arizona's last planning effort called "Moving to Higher Grown." Contrary to this perception, many growers rely on alfalfa as a major part of their income. It is a perennial crop, grown year round for 3 to 5 years and often longer. Those that consider it of minor importance in Arizona are misinformed.

10 Year Summary (Feb 11 - Feb 24, 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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