Alfalfa Stem Nematode of Alfalfa
Alfalfa stem nematode (Ditylenchus dipsaci) is the most important plant-parasitic nematode of alfalfa worldwide. Alfalfa stem nematodes infest buds, stems, roots, crowns, and seeds. Symptoms include stunted plants exhibiting yellowish, shortened stems, short internodes, and node swelling. “White flagging” occurs on leaf and stem parts caused by lack of chlorophyll due to nematode feeding. Leaf distortion and curling may be observed, along with swollen buds that do not elongate. Stem blackening can occur and stems per crown are gradually reduced until plant death occurs. Alfalfa stem nematodes may cause plants to be more susceptible to other pathogens.
“White flagging” occurs on leaf and stem parts caused by lack of chlorophyll due to nematode feeding.
“White flagging” occurs on leaf and stem parts caused by lack of chlorophyll due to nematode feeding. Howard F. Schwartz, Colorado State University, Bugwood.org.
Symptoms of alfalfa stem nematode in an alfalfa field.
William M. Brown Jr., Bugwood.org
After hatching, nematodes infest developing buds. Nematodes feed and reproduce inside stems, producing enzymes which cause the stem symptoms described above. Several generations can occur annually. Risk is greatest in fields with heavy soils and irrigation, and in places that receive high amounts of rain. High temperatures and lack of moisture limit nematode movement within the plant.
Alfalfa stem nematodes are best managed by planting resistant cultivars. Rotation to non-host crops for two to three years can reduce nematodes in the soil. Prevent new infestations by planting nematode-free seed and sanitizing harvest equipment.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
“White flagging” occurs on leaf and stem parts caused by lack of chlorophyll due to nematode feeding. Howard F. Schwartz, Colorado State University, Bugwood.org.
“White flagging” occurs on leaf and stem parts caused by lack of chlorophyll due to nematode feeding. Howard F. Schwartz, Colorado State University, Bugwood.org.
Symptoms of alfalfa stem nematode in an alfalfa field. William M. Brown Jr., Bugwood.org.
Symptoms of alfalfa stem nematode in an alfalfa field. William M. Brown Jr., Bugwood.org.
Gallery images courtesy William M. Brown Jr., Bugwood.org and Howard F. Schwartz, Colorado State University, Bugwood.org.
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