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Alfalfa

Diseases and Nematodes—Spring

On this page
  • Common leaf spot
  • Downy mildew
  • Phytophthora root and crown rot
  • Spring black stem
  • Stemphylium leafspot
  • Stem nematode

Several leaf and stem diseases occur in alfalfa in the spring. Compare field symptoms to the photos below and keep records of diseases you see. Some diseases can be reduced by adjusting harvest or irrigation practices. Names link to more information on identification and management.

Click on photos to enlarge
Symptoms Close-up view
Common leaf spot
Common leaf spot
Identification tip: Leaves of infected plants are covered with small brown-to-black spots.
Close-up of common leaf spot
Common leaf spot
Identification tip: Infected leaves have raised fruiting bodies in the middle of brown leaf lesions.
Downy mildew
Downy mildew
Identification tip: Infected leaves are spotted with a distinctive pale-green color.
Close-up of downy mildew
Downy mildew
Identification tip: Blotches on the upper sides of infected leaves are gray-green to tan.

Phytophthora root rot infection can devastate large areas of a fields
Phytophthora root and crown rot
Identification tip: Leaves of infected plants turn yellow or tan and drop. Phytophthora can infect large areas of alfalfa in a field.

Brownish streaks in roots infected by Phytophthora.
Phytophthora root and crown rot
Identification tip: Red-orange-to-yellow streaks spread up from infected root tips.

Small black spots of spring black stem
Spring black stem
Identification tip: Small black spots cover leaves and stems of infected plants.
Close-up of spring black stem lesions
Spring black stem
Identification tip: Spring black stem lesions often extend to the petiole.

Stemphylium leafspot
Stemphylium leafspot
Identification tip: Infected leaves are speckled with light spots.

Close-up of infected leaves-Stemphylium leafspot
Stemphylium leafspot
Identification tip: Infected leaves develop dry, brownish lesions bordered by a dark ring.

Crop damaged by stem nematode.
Stem nematode
Identification tip: Look for flagging alfalfa leaves.

Damaged plant
Stem nematode
Identification tip: Damaged plant showing dead stem buds, stunted shoots, and swollen internodes.


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