Yuma County, Arizona
December 3, 2001
Yuma County Office
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. We have observed seedling soybean, which is very frost sensitive, survive when air temperatures in the 20s were reported.
Insect Management: Blue alfalfa aphid is a serious pest during the winter and spring months in the low desert. Blue alfalfa aphid is distinguished from pea aphid by uniformly dark antennae. Pea aphids have lighter antennae with dark bands at each joint. 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 growth 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: Strong winds blow millions of weed seeds into irrigation
ditches. Many of these drop out around turn outs where the flow slows
although some are carried throughout the field. Efforts have been made
to filter these seeds out of irrigation water although a practical technique
has not yet been developed.
10 Year Summary (Nov 20, 2001 to Dec 3, 1992-2001):
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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Information provided by:
Barry Tickes, firstname.lastname@example.org Extension Agent, Yuma County
Michael Ottman, email@example.com Agronomy Specialist
College of Agriculture, The University of Arizona.
Eric Natwick, firstname.lastname@example.org UCCE Imperial County - Farm Advisor
University of California, Davis, CA.
Material written December 3, 2001.
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