Yuma County, Arizona
December 4, 2000
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 low 20s were reported.
Insect Management: Cowpea aphid (picture) is a black aphid that has become a serious pest of new and established stands of alfalfa. Western Arizona and southern California alfalfa stands became heavily infested in November and this problem is expected to continue into the spring months. When stands of alfalfa become heavily infested with cowpea aphid, treatment with an insecticide may be warranted to prevent yield loss due to stunting and leaf drop, and to prevent honeydew and sooty mold contamination. Treatment thresholds have not been established for cowpea aphid on alfalfa. Seedling alfalfa may be more susceptible to damage from cowpea aphid.
Weed Control: Pursuit can be applied to seedling alfalfa and will
control a broad spectrum of broadleaf weeds. It will suppress but not
kill many grasses. Weeds that are not controlled include prickly lettuce,
sowthistle and lambsquarter. Stunting of seedling alfalfa will occur for
10 Year Summary (November 21, to December 4, 1991-2000):
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, email@example.com Extension Agent, Yuma County
Michael Ottman, firstname.lastname@example.org Agronomy Specialist
College of Agriculture, The University of Arizona.
Eric Natwick, email@example.com UCCE Imperial County - Farm Advisor
University of California, Davis, CA.
Material written December 4, 2000.
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