Potato

Introduction

Potato (Solanum tuberosum) is a cool season crop that produces best yields when temperatures average slightly below 70ºF during the growing season. Potatoes will grow well on a wide range of soils and are especially well suited for New England. The best soil for potatoes is well-drained and medium-textured. Potatoes produced on light, sandy, loam soils generally have a more desirable shape and a brighter skin color than those grown on heavier clay-type soils. Poorly-drained soils favor disease development and may result in reduced plant stands, low yields and poor quality.

Types and Varieties

In addition to the varieties listed below, there is a good list of varieties with resistance to particular diseases in the Cornell Organic Potato Production Guide. 

PVY: potato virus Y; PLRV: potato leafroll virus

Early-Maturing

• Algonquin - buff skin, white flesh
• Caribe - purple skin, white flesh. Resistant to some common scab and PLRV.
• Cala Rosa - red skin, yellow flesh. Resistant to hollow heart.
• Chieftan - red skin, white flesh. Scab and late blight resistant.
• Dark Red Norland - rich dark red skin, white flesh. Tubers round to oblong. Moderately resistant to common scab, stores well.
• Natascha - yellow skin, yellow flesh. Reseistant to Rhizoctinia and PVY
• Red Gold - pink skin, yellow flesh. Intermediate resistance to scab.
• Satina - yellow skin, yellow flesh. Highly resistant to potato late blight and common scab. Stores well.
• Superior - buff-colored skin, white flesh. Oval. Moderately resistant to common scab.
• Yukon Gem - yellow skin, yellow flesh. Resistant to scab and late blight.
• Yukon Gold - yellow/buff-colored skin, medium yellow flesh. Resistant to net necrosis and has high specific gravity. Storability is excellent with long dormancy.

Mid-Season

• Adirondack Blue/Red - deeply colored varieties for mid-season.
• Caribou Russet - russet skin, white flesh. Moderately resistant to scab and Verticillium.
• French Fingerling - pink skin with yellow flesh that is splashed with pink. Longer tubers than most fingerling varieties. Resistant to scab.
• Gold Rush - russet type. Resistant to hollow heart, moderately resistant to Verticillium and scab.
• Kennebec - smooth buff-colored skin with white flesh. Some resistance to foliar late blight. Susceptible to scab, Rhizoctinia, Verticillium, and pinkeye.
• Norland - smooth red skin, white flesh. Moderately resistant to common scab, PVY and PLRV. Sensitive to air pollution (ozone).
• Red LaSoda - bright, deep red skin, white flesh. Round to oval tubers. Moderately resistant to early blight, tolerant to heat and drought.
• Red Pontiac - red-skin, oblong to round tuber. Fairly drought tolerant.

Late-Maturing

• Coastal Russet - long, slightly flattened tubers with moderately russeted skin
• Katahdin - round white cultivar, high yield potential. Has some resistance to PVY and PLRV and is tolerant of drought conditions. Susceptible to late blight, common scab.
• Russet Burbank - russeted long-tuber cultivar with high specific gravity. Resistant to common scab and blackleg. Highly susceptible to PVY.
• Russian Banana - light yellow skin, yellow flesh, banana-shaped tubers. Moderately resistant to common scab.

Soil Fertility

Lime and fertilizer should be applied according to soil test results and potato variety. If the variety is resistant to common scab, soil pH should be maintained at pH 6.0 to allow for rotation crops. If the cultivar to be raised is common scab susceptible, then the soil pH should be maintained at pH 5.0-5.2. Growers should be aware that acid scab, a scab organism that is active at low soil pH, is found in some areas; in these situations, soil pH should be raised to pH 6.0 and a scab-resistant cultivar utilized.

Nitrogen is the most critical element from the standpoint of yield and quality. Excessive nitrogen can delay maturity, decrease quality and adversely affect fry color for processing crops. Too little nitrogen will reduce yields. For most varieties, the amount of nitrogen per acre is usually 140-150 pounds. Higher rates can be used for late-maturing varieties such as Russet Burbank and slightly less for early-maturing varieties such as Kennebec. Apply P and K according to soil test results.

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR POTATO

Where all Fertilizer is Applied at Planting Time

*APPLY 125 LB K20/A BROADCAST

Where Sidedressing is Used

*APPLY 125 LB K20/A BROADCAST

Planting 

Because potatoes are propagated vegetatively, diseases can be carried over between generations. Therefore it is important to plant only certified or foundation seed which has met specific conditions for production practices and disease tolerances. Planting good seed is an essential step to producing a high-quality crop.

Seed should be stored at 38-40ºF with relative humidity maintained at 95%. Seed taken from cold storage should not be planted or cut immediately. Tubers should be warmed gradually to 50-55ºF, 7-14 days prior to cutting or planting. Good ventilation and 90% relative humidity should be maintained during this process. Cut seed pieces should be blocky, have at least one eye and weigh 1.5-2 oz.

Amount (hundredweight) of Seed Needed to Plant One Acre

The more uniform in size and weight the seed being planted, the more accurate the planter will perform. The ideal soil conditions for planting potatoes are 50-60ºF and half field capacity for moisture content as these encourage wound healing of seed pieces and rapid growth. A well-prepared seedbed is desirable and will facilitate accurate planting. Over-preparation of the seedbed should be avoided because of crusting and compaction problems. Do not plant cut seed in soil below 45ºF to avoid seed piece decay.

Suggested Seed Spacing

Close spacing in the row (e.g. 6-8") aids in reducing tuber size and increases the number of tubers set. Using close spacing can reduce the occurrence of hollow heart and growth cracks. Seed pieces should be planted 2-4" below the soil level; this will reduce problems with sunburned tubers. For rapid emergence, no more than 2" of soil should cover the seed piece after planting. Where seed is planted deeper than 2", drag-off (removal of the excess soil from the top of the hill) may be employed to encourage rapid emergence. Rapid emergence should be encouraged to reduce problems with soilborne pathogens such as Rhizoctonia.

Green Sprouting

The practice of pre-sprouting seed potatoes is called green sprouting or chitting. This accelerates plant emergence and speeds the development of marketable tubers, resulting in a gain of 7-10 days to marketable tubers. This practice is often combined with close plant spacing (about 6"). The tubers are harvested when small and often sold in quart baskets as new potatoes. 

About 6 weeks prior to planting, spread whole seed tubers in open-top crates, boxes or flats, 1 layer deep with the eyes up. Egg cartons for small seed lots work great. Keep them in a warm place (approximately 70ºF) in medium light intensity (bright shade). Direct sunlight is not recommended. The warmth stimulates the development of strong sprouts, which in the presence of light, will remain short and stout and will not easily be broken off during the planting process. Cut the seed into pieces when the sprouts are about 1" in length. Cutting seed pieces prior to green sprouting will dry them out and reduce quality.

Cultivation and Hilling

Hilling allows the use of a shallow planting depth to speed plant emergence, while providing the soil depth necessary later in the season for proper tuber development and protection from sunlight, adverse temperatures, and swings in moisture level. Begin hilling and cultivation operations  after the plants begin to emerge and complete prior to the plants filling half of the row to minimize damage to foliage. Discs, rolling cultivators, hillers or implements with winged cultivator teeth may be used. For best results, hills should be flat and broad rather than narrow and peaked. Cultivation during hilling aids in mechanical weed control and soil-applied herbicides can be incorporated at this time.

Sprout Inhibitors

Sprout inhibitors should be used only in conjunction with good storage management. Federal law requires that shipping containers carrying potatoes treated with postharvest sprout inhibitors be labeled with the chemical name of the inhibitor. When small bags are shipped in master containers, only the master container needs to be labeled. Do not treat seed potatoes.

• Field Application: Apply 3 lb. a.i. maleic hydrazide/A to healthy, green, non-water-stressed potato vines at least 2 weeks before application of any vine killer. Apply when most of the tubers are 1.5"-2" in diameter. If rain comes within 24 hours of application, effectiveness will be reduced. Do not apply at temperatures above 85ºF. See label for additional information.
• Postharvest Custom Applications:  Bulk storage equipped with good ventilation through the pile or pallet box storages can be treated with an aerosolized form of chloropropham (CIPC), sold under a variety of trade names, or Amplify (2,6-diispropylnaphtalene), applied to the storage area by licensed custom applicators. Application should be only after harvest cuts and bruises have healed (two to three weeks after harvest). Low doses can increase internal sprouting. Seed potatoes should not be placed in treated storage at any time. These are also available as emulsifiable concentrates added to wash water for prevention of sprouting in marketing channels. Do not use the herbicide formulation for sprout control. 
• Postharvest Application: Sprout Torch (clove oil) can be used as an aerosol or a spray to temporarily eliminate sprouts on potatoes in storage. Do not use on stored seed potatoes.  Do not allow vapors to come in contact with storage areas used for seed potatoes within 60 days of storing seed potatoes.  Do not apply in the field.

Vine Desiccation

Potato vines should be desiccated approximately twenty-one days prior to harvest to ensure good skin set on tubers that are to be stored.  Growers should be aware that rapid vine desiccation, whether from chemical or mechanical methods, could cause stem-end discoloration.

Mechanical desiccation practices, such as mowing or rotobeating, is not recommended for seed production.  Care should also be taken not to rotobeat so vigorously as to promote a Fusarium infection at the stolon attachment on tubers.

Organic methods of vine killing: Potatoes need 2-3 weeks between vine kill and harvest to promote tuber maturity and adequate skin set. Mature skin protects tubers from disease, resists skinning and bruising during harvest and transport, and prolongs tuber storage life. Optimally, vine killing is accomplished mechanically using a flail mower. A flame weeder might be used several days after mowing to assure complete vine kill. Care should be taken to minimize damage to tubers by mowing equipment or by dislodged rocks that can also injure tubers. Vines can also be allowed to senesce naturally by reducing water applications in some cultivars. Another option is to allow frost to kill the vines. However, potatoes left to mature in the ground for 2- 3 weeks after a frost are susceptible to damage by additional frosts and disease.

Defoliants/Dessicants/Harvest Aids for Potato

With chemical desiccation, rates should be reduced if potato plants are stressed.  Please refer to the label of the product being used. Thorough coverage is important for all these products as they are contact herbicides. Field observations suggest the following ranking of desiccants in terms of speed of stem desiccation: paraquat (fastest) > diquat > glufosinate (slowest). This implies that the risk of stem end discoloration is greater with paraquat than with the other vine desiccants.

Please note that potato plants are susceptible to diseases and should be protected from potato late blight as long as green plant material is visible

NOTE: ALWAYS FOLLOW LABEL INSTRUCTIONS. The information provided here is based on product labels at the time of writing. If there is any discrepancy between the label and the information below, follow label instructions. The current label for any given product is "the law" regarding its application.

• carfentrazone (Aim EC): PHI 7d, REI 12h, Group 14.  Apply 3.2 to 5.8 fl oz/A to potatoes in the later stages of senescence for desiccation of potato foliage and vines. AIM EC will also desiccate late season susceptible broadleaf weeds to aid in tuber harvest. Adequate desiccation is achieved within 14 days after the initial treatment is applied. If the potato crop is in the active vegetative growth stage when desiccation is initiated, two applications may be required to provide desiccation of leaf and stem tissue (not to exceed 11.6 fl oz/A per season). Dense potato canopy, large plant size and environmental conditions not conducive to product absorption or activity will reduce initial application efficacy and increase the need for a second application. If a second application is necessary, apply at 7 to 14 days after the first application. Thorough coverage of the potato plant to be desiccated is essential. Use a sufficient volume of water to obtain thorough coverage of the potato leaves and vines.
• diquat (Reglone): PHI 7d, REI 12h. Suitable for seed and storage. Apply 1 to 2 pt/A. Always use a spray adjuvant (0.1 to 0.5% v/v NIS). Rainfast in 30 minutes. A second application may be made depending on density of vine growth. A 5 day interval is recommended between applications. Not to exceed 4 pt/A per season. Minimum spray volume of 20 gal/A.
• glufosinate-ammonium (Rely 280): PHI 9d, REI 12h. NOT for seed. Apply 21 fl oz/A at the beginning of natural senescence of potato vines. Do not split this application or apply more than one application per harvest. Potato varieties with heavy or dense vines may require an application of another desiccation product to complete vine desiccation. Thorough coverage of the potato vines to be desiccated is essential. Use a sufficient volume of water (20 to 100 gpa) to obtain a thorough coverage of the potato vines. Vary the gallons of water per acre and the spray pressure as indicated by the density of the potato vines to assure thorough spray coverage. Increase the spray volume to at least 30 gallons of water per acre when the potato vine canopy is dense or under cool and dry conditions. Apply with the spray boom as low as possible to achieve thorough coverage of the potato vines for best control and to minimize drift potential. Do not make more than one application per year and do not exceed 21 fl oz/A per application. Not for use on potatoes grown for seed.
• paraquat (Parazone 3SL): PHI 3d, REI 24h. Maine and Massachusetts only. For Fresh Market potatoes only. Not registered as a vine desiccant for storage or for seed potatoes. Potatoes must be harvested promptly after desiccation and immediately processed or consumed. Storage may result in tuber decomposition. Apply 0.7 to 1.3 pt/A in minimum spray volume 20 gal/A. Split applications may be made with a minimum of 5 days between applications.  Do not apply more than 2.6 pt/A per season.  Always use either NIS at 0.125% v/v (if NIS is less than 75% surface-active agent use 0.25% v/v), or COC at 1.0% v/v.  Rainfast in 30 minutes.  Do not apply to drought-stressed potatoes.  Application to immature potato foliage will not give complete desiccation.
• pelargonic acid (Scyth): REI 12 hr. Use 5-10% v/v solution in 75-200 gal/A. Repeat application as required to maintain desirable level of desiccation.
• pyraflufen-ethyl (Vida):  PHI 7d, REI 12h.  Apply when the crop is in the early stages of senescence for best results.  Apply up to 5.5 fl oz/A. The product may be tank-mixed or used in sequence with other desiccant products for improved desiccation.  Minimum spray volume is 20 gal/A.  A second application may be made (min 7 day interval). Do not exceed 11 fl oz/A per season. Label suggests that it may not be effective in burning down grassy weeds.

Harvest

Premature harvesting can result in reduced yields and lower specific gravity. On the other hand, if harvesting is delayed too long, frost and diseases can cause serious losses. Proper operation of the harvesting equipment and careful handling can reduce the amount of damage from bruising. Potatoes should not be allowed to fall more than 4-6" and all equipment surfaces should be padded. The ideal temperature during harvest is 60-70ºF. If potatoes are harvested at temperatures below 55ºF, considerable bruising is likely to occur. If tubers are harvested during hot weather (above 80ºF) and they cool off slowly, the likelihood of storage rot is increased. Information on bruise testing is available from the University of Maine Cooperative Extension.

Storage

Healing of cuts and bruises is most rapid at high relative humidity (95%) with a tuber temperature of 50-60ºF and adequate through-the-pile ventilation. This temperature should be provided for 2-3 weeks at the beginning of the storage period. This process is called suberization. Effective suberization will reduce evaporative weight loss and prevent rot organisms from entering damaged tubers. After suberization, the temperature should be lowered gradually to 40ºF for tablestock or seed or maintained at 50ºF for chip stock varieties. When a rot potential such as field frost, late blight or ring rot is present, the curing period should be eliminated, the temperature dropped and the ventilation increased. The crop should be utilized as soon as possible.

An important aspect of potato pest control is to provide a pathogen-free storage environment. All storage and potato handling equipment surfaces should be thoroughly cleaned and disinfected prior to handling and placing the crop into storage. Surfaces should be well moistened by the disinfectant spray. Spray bin walls until there is a slight runoff.  Several disinfectant materials are available: sodium hypochlorite products (Agclor) and peracetic acid products, hydrogen peroxide, and hydrogen dioxide products (GreenClean Liquid 5.0, PeroxySan X15, Sanidate, Storox). Please consult the labels for specific directions.

Temperature control is best achieved with forced air ventilation that is controlled thermostatically by an air proportioning system. Air flows should not exceed 1.0 cu ft/cwt/min. Storage relative humidity should be as high as possible without causing condensation on the storage walls and ceilings. Good insulation properly protected with a vapor barrier reduces danger of condensation.

Pre-storage Fungicide Treatment

Treatment of potatoes (seed and tablestock) with thiabendazole (Mertect 34ºF) as they go into storage has produced excellent control of Fusarium dry rot in storage. However, resistant isolates of Fusarium are now common. Preventing cuts and bruises is the best defense against this disease. Growers may consider, as an alternative, treatment of tubers going into storage with products containing mono-and di-potassium salts of phosphorus acid (Phostrol) to reduce the tuber-to-tuber spread of potato late blight and pink rot as the tubers enter storage. These chemicals should be applied uniformly in a fine mist or fog as tubers pass over a roller table or bin loader. The rolling motion will facilitate even coverage. Do not saturate the tubers.