HPIPM:Potato Black Scurf View Black Scurf
From Bugwoodwiki
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Author: Howard F. Schwartz and David H. Gent
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Contents |
Identification and Life Cycle
Black scurf is caused by certain strains of the fungus Rhizoctonia solani, and occurs wherever potatoes are grown. R. solani has a very broad host range, but the strains that attack potato (mainly AG-3) generally do not attack other hosts. Disease is initiated from soil-borne or seed-borne sources that infect developing sprouts, stolons, and roots. Infection may occur any time during the season, but young tissues are most susceptible and are most severely infected when emergence is delayed in cool soils. The pathogen can survive several years as mycelium or dormant resting structures (sclerotia) in soils, organic matter, and crop debris. Soilborne and seedborne inoculum can both be important in the black scurf development.
Plant Response and Damage
Black scurf appears on tubers as dark brown to black, irregularly-shaped sclerotia on the surface of tubers that resemble soil that will not wash off. Sclerotia range in size from small to large, and may be flat to slightly raised, but do not penetrate the periderm. Black scurf reduces tuber marketability, seed quality, and may also reduce yield. The black scurf pathogen also causes Rhizoctonia stem canker.
Management Approaches
Biological Control
No biological control practices have been developed for black scurf.
Cultural Control
Plant high quality seed free from the black scurf pathogen in warm, well prepared soils that promote rapid germination. If soils are cool (below 46ºF), shallow planting (2 inches from the surface) will reduce time to emergence and sprout infection, but not root and stolon infection. Crop rotations of at least 2 years between potatoes will reduce soilborne inoculum, but longer rotations may be necessary in cool, wet production areas. Potato varieties vary somewhat in their reaction to black scurf; highly susceptible varieties should be avoided if possible.
Chemical Control
Fungicides applied as broadcast, in-furrow, or seed treatments reduce black scurf severity, but are most effective when combined with cultural practices that reduce seed and soil-borne inoculum.
| Common/Trade Name | Rate | Remarks |
|---|---|---|
| Fludioxonil | ||
| Maxim | 0.5 lb per 100 lb seed | Also controls Fusarium dry rot, and seed-borne Helminthosporium solani (Silver scurf); Does not control bacterial diseases; Resistance is possible. |
| Maxim MZ | 0.08 – 0.16 fl.oz per 100 lb seed | Also controls Fusarium dry rot, and seed-borne Helminthosporium solani (Silver scurf); Does not control bacterial diseases; Resistance is possible. |
| Maxim 4FS | 0.08 – 0.16 fl.oz per 100 lb seed | Also controls Fusarium dry rot, and seed-borne Helminthosporium solani (Silver scurf); Does not control bacterial diseases; Resistance is possible. |
| Maneb | ||
| Seed Treatment for Potatoes LD (plus Streptomycin Sulfate) | 1 lb per 100 lb of seed | Also controls Fusarium dry rot and blackleg; Apply for thorough coverage to whole or cut seed. |
| Thiophanate-methyl | ||
| TOPS 2.5D | 1 lb per 100 lb of cut seed | Also controls Fusarium dry rot; Treat cut seed; resistance of some organisms is possible. |
| TOPS 5 | 0.5 lb per 100 lb of cut seed | Also controls Fusarium dry rot; Treat cut seed; resistance of some organisms is possible. |
| TOPS MZ
(plus Mancozeb) | 0.75-1.0 lb per 100 lb of cut seed | Also controls Fusarium dry rot and seedborne silver scurf and late blight; Treat cut seed; TOPS MZ is not efficacious against systemic seed-piece infections or airborne (secondary inoculum. Resistance is possible. |
| In-furrow fungicides | ||
| PCNB | ||
| Blocker 10G and 4F | Apply as in-furrow granular 1.65 lb/1000 linear ft. of row (25 lb/A) in 8.5” bands or as in-furrow.
Spray 5.2-10.4 fl.oz/1000 linear ft. of row (5 – 10 pt/A) in 8.5” band. Cover during hilling. Use 10 – 2- gal water carrier. | Do not harvest within 45 days of application |
| Azoxystrobin | ||
| Quadris | Apply 0.4 – 0.8 fl.oz/1000 linear feet of row in 5–15 gallons of water in 6-7” band. Cover during hilling. | |
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.
