POTATO HEALTH MANAGEMENT IN NORTH CAROLINA Marc A. Cubeta, Extension Plant Pathologist Nancy G. Creamer, Extension Horticulturist Carl R. Crozier, Extension Soil Scientist David Monks, Extension Horticulturist/Weed Scientist Kenneth A. Sorensen, Extension Entomologist

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Vegetable Disease Information Note No. 23
Department of Plant Pathology
North Carolina State University

Potatoes (Solanum tuberosum) are grown in most North Carolina counties, however, commercial potato production is concentrated primarily in eastern North Carolina. Approximately 19,000 acres of potatoes were produced each year from 1991 to 1995 in North Carolina. Eighty percent of the potatoes produced commercially in NC were processed into potato chips, while the remainder were sold as fresh market (table stock) potatoes. Potato yields in eastern North Carolina usually vary between 145 to 200 hundredweight (CWT) per acre. The statewide average yield of potatoes in North Carolina was approximately 177 CWT with an estimated value of $6.34 per CWT (1991-1995). Although some growers typically produce 250 CWT and occasionally 400 CWT in some years; potato yields less than 100 CWT are also common. Low yields are often related to the short season (90 to 110 days) imposed by planting conditions in late winter and marketing demands in early summer. Diseases, insects, soil fertility, stand establishment and weeds can also influence potato yields.

Costs of potato production per acre for fields with high yield potential are usually comparable to those with low yield potential, and in some cases actually less. For example, growers with high yields often apply less fertilizer to reduce production costs without sacrificing potato yields and profits. Potato health management practices that reduce fertilizer input also decrease the chance of fertilizer salt injury and negative environmental impacts.

The purpose of this information note is to outline potato health management practices that avoid losses caused by diseases, insects, improper soil fertility, poor stand establishment and weeds. The management practices presented in this publication are not specific for each farming operation, but they are intended to introduce concepts that can be used to develop economical and effective management strategies.

MANAGEMENT PLANNING AND FIELD SELECTION

1. Rotate crops three or more years out of potato, if possible. This is essential for Colorado potato beetle resistance management and reducing soilborne diseases.
   
2. Assess weed problems in previous spring and fall.
   
3. Determine herbicide used in the previous two years.
   
4. Sample soils for nematodes in the fall and request species identification of the lesion nematode (Pratylenchus penetrans).
   
5. Sample soils for nutrient and pH analyses in the fall.
   
6. Avoid fields with drainage problems and shallow hard pans.
   
7. Determine wireworm hazard: high if previous crops were corn or sorghum, or the field has a history of wireworm. Solar bait traps can be used to determine wireworm species and relative population levels.
   
8. Consider regulations on aerial application of pesticides, use of wetlands and protection of endangered species. Contact the North Carolina Department of Agriculture, Pesticide Section, if you have specific questions about these issues.
   

LAND PREPARATION

1. Clean ditches to ensure good drainage and if possible, land plane field with laser equipment to avoid standing water in fields.
   
2. If present, break hard pans by subsoiling. Minimize disking and unnecessary use of tillage equipment. Avoid "working" wet soil because hard pans can develop quickly.
   
3. Lime and fertilize according to soil test reports. Broadcast fertilizer if soil soluble salts are a problem. Consider a split nitrogen application between pre-planting and at planting or emergence.
   
4. Prepare rows and treat with a fumigant nematicide if needed (see "5" under PLANTING).
   

SEED

1. Purchase and use high quality, certified seed from reliable sources.
   
2. Carefully examine tubers for disease (common scab, Fusarium dry rot, late blight and soft rot). If possible, consider sorting "diseased and non-diseased" tubers prior to planting. Severely infected seed should not be planted.
   
3. Condition seed by maintaining pulp temperature at 50 F, or higher, for at least a week before cutting.
   
4. Cut seed with sharp knives to an average size of about 2 ounces. Seedpieces weighing less than 1.5 ounces should be discarded. Dust cut seedpieces with a drying agent or fungicide (see North Carolina Agricultural Chemicals Manual). If possible, hold cut seedpieces for 3 to 5 days at 50-55 F to promote wound healing.
   

PLANTING

1. Carefully adjust and calibrate planter to ensure proper seed placement.
   
2. If possible wait for dry, warm weather and plant seedpieces when soil temperatures are 55-60 F at four inch depth. The use of a cup planter rather than a planter with spikes ("pick planter") greatly reduces the amount of seedpiece injury and disease.
   
3. Plant seedpieces about 4 inches deep. This practice promotes rapid sprout emergence but may increase the chances of frost damage in early season plantings.
   
4. Consider using a soil insecticide (see North Carolina Agricultural Chemicals Manual) to control seed corn maggot, wireworm and early season Colorado potato beetle (adults).
   
5. Band a contact nematicide (see North Carolina Agricultural Chemicals Manual) if recommended by the North Carolina Department of Agriculture Agronomic Division based on nematode samples submitted from the field.
   

GROWING SEASON

1. Set up black light or pheromone traps around April 1 to monitor European corn borer moths.
   
2. Set up equipment to collect weather information (air temperature, relative humidity and rainfall) and use a computer program (Blitecast or Wisdom) to monitor late blight favorable weather. This information should be available from crop consultants, extention agents and specialists, depending on the specific location of your potato field.
   
3. Scout weekly starting at plant emergence (April) for European corn borer, Colorado potato beetle, late blight and early blight:
   • European Corn Borer: spray with an effective insecticide when: 50 percent of ten, tagged egg masses have hatched or are predicted to hatch by observing the "black head" stage; or five entry points are found in 25 stems; or 25 or more adult moths are caught in blacklight or pheromone traps within a five day period.

   • Colorado Potato Beetle: spray with an effective insecticide when 50 percent of the eggs in ten, tagged, orange egg masses have hatched. Where biological pesticides are used, initial application must be made at first egg hatch.

   • Late blight: Be aware of late blight occurrence in potato production areas south of North Carolina (Florida and Alabama) in January and February. North Carolina, Florida, and Alabama growers often obtain their seed potatoes from similar production areas. Use weather data and computer programs (Blitecast and Wisdom) to determine if weather conditions have been favorable for late blight development. Begin scouting fields when rows are closing and continue weekly, particularly during extended blight favorable weather. Intensively scout areas of the field where late blight may develop first (low wet areas, along edges of ditches and woods). If late blight is observed in the area and potatoes are more than two weeks away from harvest, immediately initiate fungicide applications. Continue fungicide applications on a 5 to 10 day schedule depending on disease pressure and weather conditions. Under severe disease conditions shorten the spray interval (see North Carolina Agricultural Chemicals Manual)

   • Early blight: Starting in late May observe lower leaves weekly and apply fungicides if 5 percent of the leaves are infected and harvest is more than two weeks away. Continue fungicide applications on a 5 to 10 day schedule depending on disease pressure and weather conditions. It is recommended that fungicides be used for managing early and late blight in an integrated pest management system.
     

1. Adjust and operate harvesting, grading, and packing equipment to minimize tuber bruises and injuries to maintain tuber quality.
   
2. Move harvested potatoes quickly to a cool place and keep dry, do not park loads of potatoes in the sun.
   
3. Use chlorinated water for washing potatoes.
   
4. Remove soil from grading chain and destroy cull potatoes from the packhouse and fields. Do not apply cull potatoes and soil from grading chain to potato production fields.
   
5. After harvesting, disk and destroy volunteer potatoes.
   
6. Avoid unnecessary insecticide sprays on crops preceding or following potatoes to lessen the risk of Colorado potato beetle resistance.
   
7. Avoid contamination problems in storage with potato tuberworms.
   

RECORDS

1. Keep field records of where potatoes were planted and crop performance and problems encountered in the fields such as Colorado potato beetles, wireworms, weeds, flooding, poor growth or quality of tubers, and other problems.
   
2. Record all pesticides used.
   
3. Refer to these records in selecting fields (see FIELD SELECTION).
   

WINTER

1. Stay updated on changing technology and procedures by participating in county, regional, state, and national potato meetings, and reading potato production manuals, newsletters, and other publications.
   
2. Assess last year's growing season, review field records, and begin planning for next year's crop. Extension agents, specialists, and crop advisors are sources of information and can assist in planning.
   
3. Order seed, fertilizer, and pesticides early.
   
4. Service and repair equipment.
   

ADDITIONAL INFORMATION

Coates, J., ed. 1992. Integrated Pest Management for Potatoes in the Western United States, University of California, Oakland, CA

Creamer, N.G. 1996. Potato Varieties, Horticulture Information Leaflet #22-B, North Carolina State University, Raleigh, NC.

Hooker, W.J., ed. 1986. Compendium of Potato Diseases, American Phytopathological Society Press, St. Paul, MN.

Rowe, R.C., ed. 1993. Potato Health Management, American Phytopathological Society Press,
St. Paul, MN.

Sanders, D.C., Duncan, H., and Sorensen, K.A. 1993. Commercial Potato Production in Eastern North Carolina, Horticulture Information Leaflet #22,North Carolina State University, Raleigh, NC.

Sorensen, K.A. 1994. Potato Tuberworm, Department of Entomology Insect Note #3, North Carolina State University, Raleigh, NC.

Sorensen, K.A., and Nault, B.A. 1995. Life History and Management of the Colorado Potato Beetle in North Carolina Potatoes, Department of Entomology Insect Note #45, North Carolina State University, Raleigh, NC.

Sorensen, K.A., and Nault, B.A. 1996. Life History and Management of European Corn Borer in Potatoes, Department of Entomology Insect Note #2, North Carolina State University, Raleigh, NC.

This page (http://www.ces.ncsu.edu/plymouth/pubs/potatoHealth.html) was created by Marc A. Cubeta, Ph.D. Extension Plant Pathologist and Bruce A. Emmons, Area Specialized Agent, Information Management. The authors would like to acknowledge Frank Winslow, Washington County Extension Agent; Tom Campbell, Pasquotank County Extension Agent; Drs. Tom Melton and Jack Bailey, Department of Plant Pathology, North Carolina State University, Raleigh, NC for reviewing this publication and their many valuable comments and suggestions.

Date Created 09/26/96.
Last revised on 08/09/01.