Diseases of alfalfa (
Alfalfa stem nematode
The alfalfa stem nematode, Ditylenchus dipsaci, is a soilborne plant parasitic nematode that infects alfalfa. The nematode attacks the crown bud tissues (photo 1), causing the buds to swell, become brittle and distorted. Stem internodes are shortened and plants are stunted. The nematodes can be dissected from infected crown tissue and observed under low magnification with a stereo microscope. They are most active in cool, moist conditions, and disease can be widespread in Arizona in years with above normal winter and spring rain. Stem nematode is generally not an important problem in the low desert areas in the summer when warm soil temperatures are inhibitory to the nematode, but instances have been recorded. D. dipsaci survives in dried plant debris and to a lesser extent in soil in a dormant stage for years. It is easily moved by irrigation water and in soil carried by animals or machinery from one field to another.
Stem nematode is controlled by the use of resistant cultivars and cultural practices. Some winter-dormant varieties, such as Lahonton, are resistant. Tolerance is available in non-dormant varieties such as Lew. Tail water from infested fields should not be put on other alfalfa fields, and likewise, sheep should not be moved from an infested field to a non-infested field.
1 
July 13 , 2006