Fusarium Wilt of Alfalfa
Fusarium wilt is caused by the fungus Fusarium oxysporum f. sp. medicaginis, and is more severe in areas with high soil temperatures. Initial disease symptoms may appear on one side of the plant. Wilting shoots appear first, with newly infected plants exhibiting daytime leaf wilting with recovery during the night. Leaves and stems eventually bleach and leaves may show light red discoloration. Discolored, twisted, and stunted foliage occurs on the end of stems and plants eventually die. Inside the taproot, a defined, reddish-brown discoloration occurs. Cutting a cross section of the taproot will reveal full or partial “rings” of discolored tissue. As stands age, disease incidence increases.
Fusarium wilt symptoms in an alfalfa field.
Craig Grau
A cross section of an alfalfa taproot revealing “rings” of discolored tissue indicative of Fusarium wilt.
Craig Grau
F. oxysporum f. sp. medicaginis survives in living plant tissue, in the soil, or within plant residue. Infection occurs through taproot wounding or via small plant roots. The fungus clogs water conducting tissue and produces a toxin which causes root discoloration. The presence of root-knot nematodes can increase Fusarium wilt severity.
Fusarium wilt is best managed by planting resistant alfalfa cultivars.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Fusarium wilt symptoms in an alfalfa field.
Fusarium wilt symptoms in an alfalfa field.
A cross section of an alfalfa taproot revealing “rings” of discolored tissue indicative of Fusarium wilt.
Alfalfa roots showing a range of Fusarium wilt symptoms.
Gallery images courtesy Craig Grau.
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