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

Production Update:

Banking Water: Many growers apply more water than alfalfa needs during the winter in order to have "water in the bank" during the summer. This practice does have some merit on deep soils if irrigation water is in short supply during the summer. Subsoil moisture can contribute to yield and stand survival when alfalfa is stressed for water. Alfalfa is a deep-rooted crop and can take up water from depths of 8 feet or more. Subsoil moisture at a depth of 20 to 30 feet has been reported to contribute to alfalfa survival in drought years under dryland conditions.

Insect Management: Pea aphid (PA) (picture) is a pest of alfalfa during the spring. PA first appears in December or January but may persist into early summer if the weather remains cool. Heavy infestations of PA are distributed over most of the plant. They can deposit large quantities of honeydew, fouling harvesting equipment, supporting sooty molds growth, and lowering hay quality. Regrowth may be stunted from a moderate to heavy PA population. Several species of predacious bugs and parasitic wasps attack these PA. Sample alfalfa fields by taking 5 to 6 stem samples in at least 5 locations per field weekly when aphids appear, then every 2 to 3 days as numbers approach the treatment threshold of 40 to 50 aphids per stem for plants under 10 inches, 70 to 80 per stem for plants 10 to 20 inches tall and more than 100 aphids per stem for plants over 20 inches tall.

Weed Control: Now is a good time to apply preemergent herbicides for summer annual weeds. This may be a little early but its better to be a month early than a day late. Trifluralin (treflan) will last 3 to 6 months on well drained soils. Weeds such as dodder or sandbur can be controlled preemergence but are very difficult to control once they are established. What you see is what you don't get with preemergent herbicides.

10 Year Summary (Dec 31 - Jan 13, 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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