Sweetpotato Scurf
Vegetable Information Note 103
Charles W Averre, Extension Plant Pathologist

Each year scurf appears in North Carolina sweetpotatoes. In some cases much of the crop is affected at harvest; in other cases, only a few scurfy roots are present. Scurf reduces the market value and serious cases may be rejected by buyers. All growers should learn to control scurf by a total program: Set healthy plants, use land free of scurf, and harvest and store sweetpotatoes in clean baskets and houses. This program will also control black rot.

Facts About Scurf

Scurf is caused by the fungus Monilochaetes infuscans. The fungus grows only in the skin of the sweetpotato and produces spores (reproductive bodies) on the surface. The diseased areas are grayish-brown to black and are only skin-deep.
Scurfy roots will produce sprouts but some will be infected and many become contaminated with spores in the soil around the bedded roots.
Healthy roots may become contaminated with fungus spores from diseased roots, and contaminated crates, baskets, and storage houses. During grading operations, spores from diseased roots are dislodged with soil and distributed by air currents and contaminate containers and other sweetpotatoes.
Contaminated seed roots may become infected during presprouting at high relative humidities.
The scurf fungus only attacks underground portions of sweetpotatoes. It does not attack other crops.
The fungus will survive in field or plant bed soils.
Scurf is usually worse during rainy seasons.

Certified seed is the best source of disease-free plants.
Carefully select seed for bedding. Whether certified seed is used or not, every root should be inspected when selected. Wetting the roots makes scurf spots easier to see.
Treat the seed before bedding. Unseen contaminating spores can be killed by dipping the roots in a fungicide. See fungicides below.
Use vine cuttings or cut sprouts. Sprouts cut above the soil level, or vine cuttings, will be scurf-free. The cut sprouts or vines should be dipped to a depth of about 5 inches in a fungicide. See fungicides below.
Do not contaminate plants by placing them in contaminated containers, holding them in contaminated houses, or hauling on contaminated truck bodies. Disinfest contaminated equipment before using. See fungicides below.

Locate beds in a site known to have been free from sweetpotatoes for three years.
Plant in scurf-free soils. Rotate sweetpotatoes with other crops to eliminate scurf. In light soils, such as Norfolk sandy loam, a 2- to 3-year rotation is adequate. In heavier soils or those rich in organic matter use a 3- to 4-year rotation.
Harvest and store sweetpotatoes in clean containers and houses.
Before harvest clean and disinfest storage houses, containers, and equipment. Use chloropicrin at a rate of 0.5 lb/1000 cu. ft. or 5 fl. oz/100 cu. ft. High humidity in the storage house prior to (24 to 48 hours) and during fumigation is essential for satisfactory results. Maintain temperatures of 70 degrees F or above during fumigation. Disinfest containers by first cleaning them and then by leaving them in the house during fumigation. The floor and walls of houses that cannot be made "airtight" should be sprayed thoroughly with a fungicide, and cleaned containers dipped in a fungicide. See fungicides below.

Seed Production

The above procedure can be used to produce seed roots. Plant vine cuttings in land free of the scurf fungus. Harvest and store in clean containers in separate houses or clean houses in which diseased potatoes are not stored at the same time.

Approved Fungicides

Fungicides approved and suggested for treating sweetpotato roots, baskets or crates, and storage facilities are listed annually in the N. C. Agricultural Chemicals manual. Currently labeled fungicides for control of scurf are Botran (1.0 lb/100 gal water) for postharvest application and Mertect 340F (107 fl oz./100 gal water) and Botran (3-3.75 lb/14 gal water/1000 sq. ft.) for application in the plantbed. Follow label directions carefully.

Other Links

Plant Disease Information Notes Home Page
North Carolina Insect Notes
North Carolina Agricultural Chemicals Manual
CALS Home Page
NCCES Home Page
NCARS Home Page

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies.

Published by North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Revised Dec. 2000 by G. J. Holmes