Crop Profile for Potatoes in Idaho

Prepared June, 2000

General Production Information

Idaho is the nation’s leading potato producer and its annual potato harvest is one of the state’s leading outside income sources. The economic effect of potato production, in Idaho, is magnified by the many links in the production chain. Most of the seed potatoes planted by Idaho potato producers are grown in eastern Idaho. Most all of the potato planters and harvesters are manufactured in Idaho, and there are the "value added" products produced in the state such as dehydrated and frozen potato products and the fresh shippers.

 

Production Regions

Major production regions are adjacent to the Snake River Plain of southern Idaho, where water is available for irrigation.

 

Cropping Practices:
Soils are volcanic derived and range in texture from sandy to clay loam. The soil types are favorable for potato production. The arid climate is characterized by hot days and cool nights, and promotes excellent potato growth.

Planting begins April 1 in the Southwest and ends June 10 in the East. Cultivation is used for weed control, aeration, and proper seed depth to prevent greening of the tubers. Sprinkler irrigation is used on 99% of crop and furrow or rill irrigation is used on 1%. Irrigation allows for precise management and application of water, nutrients, and crop enhancement materials. Harvest begins after tuber maturity, usually beginning July 15 and continuing through November 15, moving from the southwestern part of the state to the east. Harvested potatoes are then placed in storage for future processing or fresh market use.

 

Integrated Pest Management Practices:
All growers practice some elements of integrated pest management (IPM). Field scouting and testing, crop rotation, planting disease free clean seed, pest forecasting and determining economic thresholds preclude pesticide application. Based on a statewide survey, adoption rates of IPM sampling and decision-aids have increased moderately since 1992.

The following are some of the IPM practices used by growers:

The use of certified seed and planting resistant or tolerant varieties are common IPM practices. In addition, potatoes are rotated with other crops such as small grains, legumes, and green manure crops to suppress the development and movement of soilborne diseases, weeds, insect, and nematode pests.

 

 


Insect Pests

The most serious insect pests are green peach aphid, Colorado potato beetle, and wireworms.

 

Green Peach Aphid (GPA)
Myzus persicae

Green Peach Aphid (GPA) is one of the most serious pests in Idaho potato production. A survey of Idaho potato growers showed that the GPA is considered a "serious pest" by 37% of the growers. It causes economic loss every year, mainly because of the transmission of potato leaf roll virus. Leaf roll is one of most serious diseases of potatoes. Aphids overwinter as eggs in peach trees and spread to potato fields, laying live young that live on the underside of potato leaves. Aphids can mechanically spread leaf roll virus to healthy plants. Damage involves stunting of the plant and serious internal browning of the tubers. Yield and quality are significantly reduced. Estimated crop loss without control ranges between 40% - 70%.

Since only a small percentage of internal disorders such as net necrosis can be tolerated and aphid flights can be heavy, very few, if any, GPA can be tolerated by potato producers, especially by seed producers. Essentially all aphids must be prevented from surviving on commercial and seed potatoes.

The action threshold in south central Idaho for aphid control is reached when population density of wingless green peach aphids exceeds 10 aphids per 50 potato leaves for 2 consecutive weeks. In southwestern Idaho, the corresponding threshold is 40 aphids per 50 leaves.

Control:

Chemical Control:
Growers will use an insecticide at planting or a foliar treatment following cultivation. Eighty eight percent of the growers scout for aphids to determine the action threshold before applying foliar insecticides.

Many insecticides registered on potatoes do not give satisfactory aphid control. The Green Peach Aphid (GPA) is one of the few insect species reported to be resistant to compounds of all classes of insecticides: organochlorines, organophosphates, carbamates, and synthetic pyrethroids.

The GPA has shown resistance to the synthetic pyrethroids, esfenvalerate and permethrin. Pyrethroids are generally not effective against aphids, but are used extensively on potatoes because they have a broad-spectrum of activity against other pests and are cost-competitive. Soil-applied insecticides give good control of early season aphids. Even with effective residues, many aphids escape and infect other plants with the potato leaf roll virus (PLRV). It is important to maintain full season aphid control to reduce the possibility of PLRV. Reducing aphid populations to tolerable levels requires a combination of control measures using cultural practices and several insecticides with different modes of action.

Alternative Insecticides:

Integrated Pest Management and Cultural Control:
Cultural control methods are an integral part of reducing populations of GPA. Prunus and other host species are treated with insecticides or eradicated to control aphids. These treatments will limit the overwintering capacity of the aphids and reduce infestation in potato fields. Growers use resistant varieties and certified seed free of PLRV. Eighty eight percent of the growers examine potato leaves for aphids.

 

Colorado Potato Beetle (CPB)
Leptinotarsa decemlineata

The Colorado potato beetle (CPB) is second in importance only to the GPA. The CPB invades potato fields as an adult and will lay 300 to 500 eggs over a 4 week period on the undersides of leaves at scattered locations throughout the fields. The eggs hatch in 4 to 9 days and the larvae feed heavily on terminal growth. Both adult beetles and larvae feed on potato leaves and stems, but the larvae are more damaging. If the larvae are not controlled, they will cause 70%-100% defoliation, ultimately death of the plant, and 40% yield loss. The adult beetles cause some damage but seldom require control.

Control of CPB is primarily with soil applied insecticides. Natural enemies are not sufficiently abundant to contain populations. While synthetic insecticides remain the most effective means for its control, resistance by the CPB to all classes of insecticides has been documented in many U.S. potato-producing regions. CPB resistance was first discovered in Idaho in the mid-1980’s. Widespread and locally diverse esfenvalerate and phosmet resistance was detected in all counties in southern and eastern Idaho in 1992. No resistance was detected to carbofuran or endosulfan. Resistance has the greatest potential to eliminate insecticides as useful tools in CPB management.

Control:

Chemical Control:

Alternative Insecticides:

Biological Insecticides:
Bacillus thuringiensis spp. tenebrionis (Novodor) – This species of Bt has been proven effective, but it is not used for conventional CPB control. It is used by the organic potato producers.

Integrated Pest Management and Cultural Control:
Ninety one percent of Idaho growers scout fields for CPB. The University of Idaho integrated pest management program has developed economic thresholds for CPB dependent upon crop value and insect control costs.

Alternative Control Practices:
There has been an increase in the use of transgenic potato varieties as one alternative control practice. In Idaho, 3.8% of the potato acreage in 1999 was planted to genetically modified (GM) potatoes. Most of these potatoes were planted as an alternative for CPB control. A very small percentage of the GM potatoes (less than 1%) were planted to control leaf roll virus and potato virus y.

 

Wireworm
Limonius californicus, L. canus, Ctenicera pruinina

This pest is considered serious by 16% of growers, and a moderate pest by 64%. Larvae feed upon potato seed pieces and underground stems during the spring. The early feeding opens the seed pieces and stems to rotting organisms (fungi and bacteria) which result in poor or weak stands. Wireworms also burrow into developing tubers, lowering quality and value of the tuber.

Detecting wireworm infestations and determining populations can be difficult. Baiting gives a poor estimate of population sizes, but is a quick method to determine the presence of wireworms. Soil assay procedures are available to estimate the number of wireworms per square foot.

Control:

Chemical Control:
Use of soil applied insecticides is the main method of control for wireworms.

Alternative Insecticides:

 

 

Diseases

There are a number of disease problems in the field and in storage situations. The important diseases occurring in the field are seed piece decay, early blight, late blight, early dying and potato leaf roll virus (PLRV). The diseases that occur in storage are pink rot, pythium leak, late blight, fusarium dry rot and early blight. Silver scurf and bacterial soft rot will follow these diseases infecting the tubers. Early blight and fusarium dry rot infect wounds that are caused from harvest. Seed potatoes have all of the above diseases with potato leaf roll virus being the most serious. Net necrosis of the potato tuber is the result of infection by potato leaf roll virus. The University of Idaho has published the Potato Net Necrosis Idaho Action Plan 2000, which assists producers manage this virus. Seed potatoes also have potato virus y (PVY). Late blight has become more serious is Idaho. The disease has been managed in Idaho, but remains a threat to growers because of new strains, and the unknown severity the disease may have. Late blight is rated by Idaho potato growers as the most serious pest problem.

 

Late Blight

Late blight is the most damaging later in the growing season. The fungus attacks stems, leaves, and tubers. If wet or damp weather continues after infection, the entire plant quickly decays. At first, the attack appears insignificant only affecting a stem or leaf in small areas of the field. However, the disease can spread so rapidly that in a few days an apparently healthy field may be severely damaged. Approximately 75% of potato acreage receive four or more fungicide applications each year at 7 to 10 day treatment intervals.

Control:

Chemical Control:
There are two types of chemical control used for late blight; protectant and systemic fungicides. Protectants are applied every seven days starting at six inches of shoot growth. Systemics are generally tank mixed with a protectant to avoid resistance. Systemics are applied after the disease has been identified.

Disease prediction models based on weather data are used in some areas. These models predict disease occurrence based on temperature and rainfall and/or humidity. They may be used to schedule foliar fungicide applications.

Cultural Control:
The University of Idaho has published the Idaho Action Plan for Late Blight which deals with preventative measures that can be taken by producers to avoid late blight infestations. The University also has a Late Blight Hotline, 800-791-7195, for the most up-to-date information on late blight.

 

Other Diseases

Chemical Control:

Integrated Pest Management:
Integrated pest management practices used by growers to reduce the incidence of diseases:

Disease Management

% Growers

Reduce source of late blight by destroying cull potatoes

96%

Plant certified seed

94%

Scout for late blight

98%

Sort/remove decayed tubers coming into storage

88%

Adjust fertility/irrigation practices to manage diseases

86%

Control weeds that are alternate hosts of diseases

82%

Post-harvest Potato Storage:
Most of the U.S. fall potato crop is stored for later marketing and processing. To obtain a constant supply to the fresh and processed potato market, potatoes are treated with a sprout inhibitor. The potatoes are treated with sprout inhibitors at least two weeks after going into storage. Typical treatment may apply sprout inhibitors later into storage usually in December.

Control:

Diseases such as late blight are treated in potato storage facilities by applying a disinfectant to the treatment water or humidification in the storage facility plenums. Post-harvest potato disinfectant dips are also available with most having a potable rinse requirement. These are often used in flume waters or directly on the potatoes. Examples include: calcium hypochlorite, peroxyacetic acid/hydrogen peroxide and chlorine dioxide.

 

Control:
Chlorine dioxide (Purogene and Anthium AGP)– This disinfectant is used in Idaho under a Section 18 Emergency Exemption provision of FIFRA. One application per year may be made directly to potatoes going into storage. It can also be added to the humidification system as either a mist in to the air stream or as a fog directly into the storage facility plenums. This treatment can be made up to five times per month of storage.

 

 

Nematodes

Nematodes are one of the major limiting factors for potato production in Idaho. Nematode infestation results in yield decline and reduction in quality thereby contributing economic loss to the industry. Predominant nematode pests identified in rhizospheres of potatoes are root knot nematodes (Meloidogyne spp.), root lesion nematodes (Pratylenchus spp.) and stubby root nematodes (Trichodorus and Paratrichodorus spp.)

 

Root-knot nematode
Meloidogyne spp.

Columbia root-knot nematode and the northern root-knot nematode have been recognized as major nematode pests on potato and found in abundance especially in sandy soils. Females feeding in the tubers and the development of live young cause enlargement or bumps in the outer layers of the tubers, rendering them useless for either fresh packing or processing. The nematodes have a wide host range leading to population increases when other susceptible crops are grown in rotation with potatoes. Damage is usually most severe following alfalfa hay crops and during years with high spring temperatures. Specific symptoms caused by root-knot nematodes include swellings, called "galls," on the roots. These galls may contain one to several adult root-knot females. They cause field damage that is localized, usually in patches of various sizes, or may be spread throughout an entire field and plants become chlorotic and stunted. Damaged roots are not able to obtain soil nutrients and above ground symptoms appear as nitrogen or micronutrient deficiencies. Plants may wilt easily, especially in warm weather, due to root damage even though soil moisture may be adequate.

 

Root Lesion Nematode
Pratylenchus spp.

The root lesion nematode Pratylenchus, a migratory endoparasite on potatoes, is a concern to potato growers because it reduces yield by indirectly weakening and increasing plant stress. This stress causes the potato plants to be more susceptible to fungal and bacterial diseases. There is also a correlation of root lesion nematodes with the incidence of verticillium wilt (early die). Five percent of the growers consider this pest to be important.

 

Stubby Root Nematodes
Trichodorus spp. and Paratrichodorus spp.

Stubby root nematodes are migratory ectoparasites and are found in sandy, moist, cool soils. Damage is profoundly influenced by soil moisture and is greater in wet seasons. These nematodes are important parasites of potatoes, not so much for the direct damage they cause but for the tobacco rattle virus they transmit to potatoes. This virus causes a disease of potato tubers called corky ringspot. Rusty brown, irregularly shaped lesions that have a corky texture appear in the flesh of the tubers. Nematode problems occur mostly in isolated sandy soil areas of southern Idaho. These nematodes have wide host ranges, making management with crop rotation difficult and relatively ineffective. Stubby root nematode is mobile in the soil and may traverse large vertical distances; therefore, enumeration and determination of a threshold level is difficult. They may survive cold winters by migrating below the frost line and undergoing dormancy.

Control:
Control of nematodes in the potato field can be achieved by chemical and non-chemical means. Non-chemical practices include prevention, crop rotation, clean fallow, early harvest application of organic manure and catch crops. Soil sampling is used by 51% of growers to determine the level of nematode infestation. When nematode population densities exceed the economic threshold, chemical nematicides will be applied by most growers.

Chemical Control:
Fumigants and non-fumigants are the two types of chemicals used for the nematode management. Fumigants are volatile compounds that produce toxic fumes when injected in to the soil. Non-fumigants are nonvolatile compounds that kill nematodes by direct contact.

Fumigants
Soil fumigation is the most cost effective chemical method for controlling root-knot nematode.

Non-fumigants
Non-fumigant systemic nematicides are the most cost effective chemical method for controlling root lesion and stubby root nematodes.

Non-Chemical Control:

 

 

Weeds

Weeds are considered one of the three most serious pests in potato production. Weeds can cause a 15% or more yield loss if not controlled. Pigweed and barnyardgrass, for example, at a density of 1 plant per yard of row can reduce potato yield by 19 to 33%. Cultivation for weed control has been shown to reduce yields. A study done with two post-hilling cultivations reduced U.S. No. 1 potato yield by 17%.

 

Volunteer Grain

Volunteer grain can be a problem before planting.

Control:

Chemical Control:

 

Grasses and Broadleaf Weeds

Primary target weeds include nightshade (host of CPB), redroot pigweed and several other broadleaf and annual species. Several control options are possible, both chemical and cultural.

Growers mound soil around the potato plants, a process called hilling. This helps to reduce greening, which occurs when the tubers are exposed to light. Some herbicides are incorporated into the soil during hilling. Cultivation is used by growers to control weeds and keep tuber greening down. If performed correctly, cultivation, with no weather delay is an effective weed control measure. However, due to the nature of weed growth and weather patterns, chemical measures are almost always a necessity. In addition, crop damage can be more severe with cultivation than with herbicides. The combination of herbicides and cultivation is essential in the production of potatoes.

Control:

Chemical Control:

Integrated Pest Management and Cultural Control:
The following IPM and cultural practices are used by Idaho potato growers to reduce weed problems:

Weed Management Practice

% Growers Using Practice

Cultivate for weed control

88%

Scout fields for herbicide need

80%

Adjust herbicide rate based on weed pressure

67%

Rotate herbicide classes to avoid resistance

65%

Choose rotational crops that compete with weeds

59%

 

Potato Vine Removal:
Potato vine removal before harvest is a common practice in Idaho. Removing vines three weeks before harvest allows stolens to loosen from the tubers, hastens tuber maturity, and sets skin. The "skin set" trigger is the vine kill process. It takes about 18-21 days for tubers to completely heal after the skin set process has started. A tough, fully mature skin provides excellent disease and bruise protection. The tough skin is also crucial to providing a quality crop during harvesting and storage. Since 90% of the potatoes are stored either on the farm or by processors and fresh pack shippers, minimizing storage loss is economically very important. Tuber maturity reduces water loss during storage, increases resistance to scuffing, decreases storage decay and increases resistance to bruising during harvest and handling. Because of the short growing season in Idaho’s production regions, vine removal requires the use of chemical dessicants or mechanical vine choppers to aid in harvest before freezing temperatures damage tubers in the soil. About 60% of growers use some type of vine removal practice.

Mechanical vine killing techniques consist of rolling to crush the vines and open the canopy or mowing, usually with a flail-type mower, to chop the vines. Many growers use a combination of methods to kill vines in order to increase the speed and the effectiveness of the vine kill. One technique used in Idaho is to pull a flail-type mower with hill-hugging rollers behind it through the field and follow this with a chemical application two or three days later.

Chemical Dessicants:

 

 

Contacts

Prepared by:
Ed Bechinski, Extension IPM Specialist, University of Idaho, Moscow, ID
Jeff Bragg, Potato grower, Jerome, Idaho.
Saad Hafez, Extension Nematologist, University of Idaho, Parma, Idaho
Ronda Hirnyck, Pesticide Program Coordinator, University of Idaho
Nora Olson, Extension Potato Specialist, University of Idaho, Twin Falls, ID
Robert Stolz, Extension Entomologist, University of Idaho, Twin Falls, ID
Maury Wiese, Plant Pathologist, University of Idaho, Moscow, ID

Contact Person:
Ronda Hirnyck, Pesticide Program Coordinator
University of Idaho—Boise Center
800 Park Blvd. Suite 200
Boise, ID 83712
Phone: (208) 364-4046
FAX: (208) 364-4035
rhirnyck@uidaho.edu

 

References

  1. Baird, Craig, Entomologist, 1999. Personal Communication. University of Idaho, Parma R & E Center, Parma, Idaho.

  2. Bechinski, E.J. 1997. Integrated Pest Management and the Idaho Potato Industry. Results of grower surveys. Div. of Entomology, Univ. of Idaho, Moscow, Idaho.

  3. Bechniski, E.J., L.E. Sandvol and R. L. Stoltz. 1995. Integrated Pest Management Guide to Colorado Potato Beetle. Bull. 757, Coll. Of Ag., Univ. of Idaho, Moscow, Idaho.

  4. Bishop, G. W., R. L. Stoltz, and H. W. Homan. 1982. Management of Potato Insects in the Western United States. WREP 64.

  5. Bragg, Jeff. 1998. Personal Communication. Potato grower of Idaho.

  6. Eberlein, C.V. 2000. Personal Communication. Univ. of Idaho, Twin Falls R & E Center, Twin Falls, Idaho.

  7. Eberlein, C.V., and R.H. Callihan. Herbicides for Weed Control in Commercial Potatoes. Bull. 709, Coll. of Ag., Univ. of Idaho, Moscow, Idaho.

  8. Eberlein, C.V., Patterson, P.E., Guttieri, M.J., and Stark, J.C. 1997. Efficacy and Economics of Cultivation for Weed Control in Potato (Solanum tuberosum). Weed Technology. Vol. 11:257-264.

  9. Guenthner, J. Preliminary results, Pesticide Benefits to growers. Coll.-Ag,Economist, University of Idaho.

  10. Lewis, M.D., M. K. Thornton, and G. E. Kleinkopf. 1997. Commercial Application of CIPC Sprout Inhibitor to Storage Potatoes. Univ. of Idaho. Cooperative Extension System, CIS # 1059.

  11. Mowry, T. M. 1994. Insecticide Resistance in the Colorado Potato Beetle. Proc. Winter Commodity School. Univ. of Idaho.

  12. Nolte, Phil, Plant Pathologist, University of Idaho, Idaho Falls, Idaho. 1999. Personal Communication.

  13. Nolte, Phil, L. Sandvol, T. Mowry, R. Stoltz, N. Olson, B. Geary, D. Corsini and J. Whitworth. 2000. Potato Net Necrosis Idaho Action Plan 2000. Univ. of Idaho, Coll. Of Agri.

  14. Nolte, Phil, K. Mohan, B. Geary, N. Olson, W. Bohl and D. Corsini. 2000. Idaho Late Blight Action Plan (Revised June, 2000). Univ. of Idaho, Coop. Ext. System.

  15. Patterson, Paul. Personal communication. 1998. Extension Agricultural Economist, University of Idaho, Idaho Falls, Idaho.

  16. Pscheidt, J.W. and C. M. Ocamb. 1999. Pacific Northwest Plant Disease Control Handbook. Oregon State University.

  17. Randall, C. R. 1993. "Management of Aphids and Leafhoppers". p 119. In: Potato Health Management. Potato Health Management Series. 178pp.

  18. Robison, M.H., J.F. Guenthner, N.L. Meyer, J.C. Foltz, S.A. Wolf, and R.L. Smathers. 1995. The role of potatoes in Idaho’s economy. University of Idaho, Idaho Agricultural Experiment Station.

  19. Schreiber, A. and L. Ritchie. Washington Minor Crops. Washington State University.

  20. Stolz, Robert, Entomologist, Charlotte Eberlein, Weed Scientist, Don Morishita, Weed Scientist, Nora Olson,Potato Specialist, University of Idaho. Twin Falls, Idaho. 1999. Personal Communication:

  21. Thornton, Michael. NatureMark Potatoes. Personal Communication. 2000.

  22. USDA--Idaho Agricultural Statistics Service and Idaho State Department of Agriculture. 1998 and 1999 Idaho Agricultural Statistics.

  23. USDA NASS. 1997. Agricultural Chemical Usage Field Crop Summaries.

  24. Univ. of Nebraska, Ag. Res. Div. Jour. Ser. #12191.

  25. Wiese, M. V, and J. F. Guenthner. 1998. Assessments of Pesticide Use in the U.S. Potato Industry. Coll. of Ag., Univ. of Idaho, Moscow, Idaho. Univ. Id. Ag. Exp. St. Pub. #9811.

  26. Western Regional IPM Project. Integrated Pest Management for Potatoes in the Western United States. 1986. Univ. of Calif, Div. Of Agri.and Nat. Resources Pub. 3316.


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