Introduction
Horseradish (Armoracia rusticana P. Gaerln., B. Mey. Scherb) is grown for its white, flesh, and pungent roots. Approximately half of the total commercial horseradish in the United States is produced in Illinois. Two other major horseradish production areas are Eau Claire, Wisconsin, and Tule Lake, California. Also, horseradish is commercially grown in Connecticut, Massachusetts, Mississippi, New Jersey, Ohio, Pennsylvania, and Washington in smaller scales.
Horseradish is a high-value crop – value of processed-products exceeds $6,000 per acre. Over the past 25 years, the horseradish growers in Illinois, and other horseradish growing areas in North America, have experienced internal discoloration in horseradish roots, causing of up to 100% yield losses. Internal discoloration of horseradish is a disease complex caused by Verticillium and Fusarium species. Other important diseases of horseradish are brittle root (Spiroplasma citri), Cercospora leaf spot (Cercospora armoraciae), Alternaria leaf spot (Alternaria brassicae), bacterial leaf spot (Xanthomonas campestris pv. armoraciae), Turnip mosaic virus (TuMV), and white rust (Albugo candida).