Yuma County, Arizona
April 7, 2003
Yuma County Office
Summer Slump: "Summer slump" is well-known by alfalfa growers as the decrease in yields that normally occurs each summer in Arizona. Yield decline with later harvests in the season occurs in most alfalfa-growing regions of the world. Factors responsible for summer decline may include temperature, day length, water stress, aging, and depletion of food reserves in the plant. The rate of maturation of the crop is probably a primary factor responsible for summer decline. In other words, the crop flowers so fast that time is not available to accumulate yields similar to the spring. Summer slump cannot be avoided in Arizona, but maintaining adequate soil moisture levels can slow yield decline. Also, increasing the cutting interval for one harvest during the late summer is recommended to promote the health of the stand during this stressful time of year.
Insect Management: Several species of Empoasea leafhoppers (picture) occur in alfalfa. Adult leafhoppers are about 1/8" long, bright green, wedge-shaped bodies. Nymphs have green wedge-shaped bodies and run rapidly forward, backward, or from side to side when disturbed. In the low desert, damage may occur from May through September. Symptoms include a yellow, wedge-shaped area at the tip of the leaf and stunting. With the first sign of injury, sample the field with a standard sweep net taking 10 sweeps in 4 to 6 areas over the entire field and count the adults and nymphs. When an alfalfa field is 2 or more weeks from harvest, treat if counts reach 5 leafhoppers per sweep. If alfalfa is within 10 days to 2 weeks of harvest, treat at 10 per sweep. If alfalfa is to be harvested in a few days, early cutting will control leafhoppers. Leafhopper infestations may be confined to the first 50 to 100 feet of the field margin. If this is the case, treat only the field edges where high leafhopper counts of treatable magnitude are found.
Weed Control: Both Select and Poast will control seedling sandbur when it has 1-3 leaves. If it gets larger than this or if it is coming back from established plants that have overwintered, neither of these herbicides will be effective.
10 Year Summary (March 25, to April 7, 1994-2003):
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.
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