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

Production Update:

Potassium Requirement: Alfalfa requires more potassium than any other mineral element. Alfalfa removes approximately 60 pounds of potassium (as K2O) per ton of hay yield. Potassium fertilization of Arizona soils, however, is generally not required. Calcareous soils of the irrigated valleys in Arizona contain 1.4 to 3.0 percent total potassium, representing 56 to 120 thousand pounds of potassium per acre-foot of soil. Less than 1 percent is water soluble and available for plant uptake. Potassium deficiency can occur in soils relatively high in total potassium if potassium is not transformed into the water soluble form fast enough to meet plant requirements. Potassium deficiency symptoms appear first as small white spots on the outer edges of the upper leaflets. In general, potassium deficiency for alfalfa in Arizona is expected to be quite rare and not a concern for the vast majority of growers.

Insect Management: Thrips do not normally cause economically important damage to alfalfa. Several species of thrips may be found in alfalfa including: Western flower thrips (picture), Bean thrips (Caliothrips fasciatus), Onion thrips, Sixspotted thrips (picture) and Caliothrips phaseoli. Feeding injury is caused when thrips rasp the leaf surface with special mouthparts and then suck up the plant juices. Such feeding causes the surface of the leaf to be whitened or silvery and somewhat flecked or stippled in appearance. Feeding, particularly near the leaf mid-rib, causes curling and distortion of the leaves; they often have a cup-like or puckered appearance (picture). There is no evidence that thrips cause yield or quality loss in alfalfa. During the fall of 2001, Caliothrips phaseoli numbers were very high in seedling and mature stands. Some seedling stands required treatment due to the combined stress of herbicide treatments, hot weather and high thrips numbers.

Weed Control: Kerb often misses weeds in alfalfa that it normally controls in other crops. This is because Kerb leaches below the germinating weed seeds when flood irrigations of 5 to 6 inches are applied. Only the most sensitive grasses are usually controlled.

10 Year Summary (Oct. 22 - Nov. 4, 1993-2002):

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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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