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

Production Update:
Seedling Cold damage: Alfalfa seedlings are thought to be the most sensitive to cold damage at the cotyledon stage before any true leaves have formed. While this may be the case under artificial conditions, in reality, the opposite seems to be true: alfalfa in the cotyledon stage is rarely damaged by cold. The temperature of the plant leaf during a cold night may be warmer than air temperature a few feet above the soil surface. A broad leaf near the soil surface may intercept heat from the soil and maintain a temperature above air temperature.

Insect Management: Blue alfalfa aphid (picture) is a serious pest during the winter and spring months in the low desert. Blue alfalfa aphid is distinguished from pea aphid (picture) by uniformly dark antennae. Pea aphids have lighter antennae with dark bands at each joint (picture). The blue alfalfa aphid first appears in December or January when it may be more abundant than pea aphid. Both species are common throughout the spring, but pea aphid is more heat tolerant and may persist into early summer. In susceptible alfalfa varieties, blue alfalfa aphid may stunt grown and infested plants have smaller leaves, shorter internodes, leaf curling, yellowing, and leaf drop. Several species of predacious bugs and parasitic wasps attack these aphids. Sample alfalfa fields weekly when aphids appear, then every 2 to 3 days as numbers approach the treatment threshold of 40 to 50 blue alfalfa aphids per stem.

Weed Control: Freezing temperatures will cause crop injury but is necessary to kill summer annual weeds such as sprangletop and sandbur. Some summer annuals are selectively killed only by freezing temperatures.

10 Year Summary (Dec. 15 - Dec. 29, 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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