Plant Health Problems
Diseases caused by Fungi:
Root and crown rot, Rhizoctonia solani, Pythium spp., Fusarium spp.
Symptoms appear as wilting and a slow or rapid collapse of the plant. The roots can appear brown and water-soaked instead of white. A water-soaked lesion can often appear at the base of the stem.
Control can be achieved by using sterile potting media, clean pots, and fungicide-treated seed. Affected plants should be rogued out and discarded. Control can be achieved by using a two-year rotation with nonsusceptible plants, such as corn, to prevent the buildup of pathogenic organisms.
Verticillium wilt, Verticillium dahliae.
The disease is caused by a fungus. Plants first appear stunted and chlorotic, but rarely die. The internal water-conducting tissue in the base of the stem can appear discolored.
Control can best be achieved by rotation with nonsusceptible crops, such as corn.
White rust, Albugo candida.
This disease is caused by a fungus and shows up as white, circular, irregular blisters on the leaves. These blisters eventually break open, and are seen to be filled with the white, powdery spores of the fungus. The fungus also attacks certain weeds, such as shepherd's purse.
The disease is rare and not important enough to require regular control measures.
Leaf spot, Alternaria brassicae.
The usual leaf spot on horseradish in Connecticut appears as fairly large, dark target spots.
Special control measures usually are not required.
Horseradish flea beetle, Phyllotreta armoraciae.
This flea beetle is about 1/8" long. It is black with yellowish wingcovers, except for a narrow black outer margin and a broader inner margin. The latter appears as a stripe on the top, broadest in the middle. It feeds upon horseradish and watercress. The females lay eggs on the petioles of the young leaves in May and the larvae burrow in the petioles, often killing some of the leaves. The insects overwinter as pupa in the ground and there is only one generation each year. Control is seldom necessary.