Silver scurf is caused by the fungus Helminthosporium solani, and probably occurs worldwide. The disease is most severe when tubers are stored for long periods of time. The pathogen is generally introduced into a field on infected seed pieces, where spores of the fungus wash down onto and directly penetrate daughter tubers. H. solani can also overwinter in soils and infect both young and old tubers. The pathogen can continue to grow, sporulate, and spread in storage. The pathogen can survive between potato crops saprophytically on crop debris and organic matter, but is not known to infect other hosts.
Silver scurf symptoms begin as tan to gray, circular lesion that form on the periderm, generally at the stolon end of tubers. When moist, lesions have a silvery appearance. Lesions eventually spread over large areas of tuber, and develop a sooty appearance where the fungus produces spores (conidia). As symptoms progress in storage, parts of the periderm may slough off. The disease is most severe on white and red-skinned varieties, but is also important on russet-skinned varieties. Silver scurf can increase tuber shrinkage in storage because of increased water loss, as well as reduce marketability and seed quality.
No biological control practices have been developed for silver scurf.
Plant only high quality seed free from the silver scurf pathogen. Practice crop rotation to reduce soilborne inoculum. Avoided delaying harvest, as silver scurf increases with time from crop maturity. Store tubers at the lowest temperature and relative humidity possible for the target market. Provide adequate ventilation to reduce condensation and dead air spaces. Thoroughly clean storage sheds with a disinfectant before storing tubers. If possible, market more severely affected fields earlier, as silver scurf losses increase in storage.
Seed treatment reduces seedborne inoculum and can reduce silver scurf losses, but is most effective when combined with sound cultural practices in the field and storage. Strains of H. solani resistant to thiabendazoles have been reported.
Common/Trade Name |
Rate |
Remarks |
Captan |
||
|
Captan 5% |
1-2 lb per bushel |
Treat whole or cut seed, rates varying with adhesion. Treat within 6 hr of cutting. |
|
Captan 7.5 Dust |
10 oz-1.0 lb per 100 lb cut seed |
Treat whole or cut seed, rates varying with adhesion. Treat within 6 hr of cutting. |
Fludioxonil |
||
|
Maxim
|
0.5 lb per 100 lb seed potatoes
|
Also controls Fusarium dry rot, Rhizoctonia stem canker, and black 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, Rhizoctonia stem canker, and black 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, Rhizoctonia stem canker, and black scurf; Does not control bacterial diseases; Resistance is possible. |
Maneb |
||
|
Maneb 75 DF |
1 lb per 10 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Maneb 80 WP |
1 lb per 10 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Seed Treatment for Potatoes LD (plus Streptomycin Sulfate) |
1 lb per 100 lb of seed |
Apply for thorough coverage to whole or cut seed. |
Mancozeb |
||
|
Dithane DF |
1.25 lb per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Dithane F-45 |
1 qt per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Dithane M-45 |
1.25 lb per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Dithane WSP |
1.25 lb per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Manzate 75 DF |
1.25 lb per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Penncozeb 75 DF |
1.25 lb per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Penncozeb 80 WP |
1.25 lb per 50 gal of water |
Dip whole or cut tubers, spread treated seed pieces in a cool place if held before planting. |
|
Potato Seet Treater 6% |
1-1.3 lb per 100 lb seed |
Apply for thorough coverage to whole or cut seed. |
|
Potato Seet Treater PS |
1 lb per 100 lb seed |
Apply for thorough coverage to whole or cut seed. |
Metiram |
||
|
Potato Seed Treater |
1-1.5 lb per 100 lb seed |
Apply for thorough coverage to whole or cut seed. |
Thiophanate-methyl |
||
|
TOPS 2.5D |
1 lb per 100 lb of cut seed |
Treat cut seed; resistance is possible. |
|
TOPS 5 |
0.5 lb per 100 lb of cut seed |
Treat cut seed; resistance is possible. |
|
TOPS MZ (plus Mancozeb) |
0.75-1.0 lb per 100 lb of cut seed |
Treat cut seed; Resistance is possible. |
In-furrow fungicides |
||
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. |
||
Categories: Potato, Disease, Silver Scurf
Date: 03/29/05