Potato

Introduc​tion

Potato (Solanum tuberosum) is a cool season crop that produces best yields when temperatures average slightly below 70°F 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 a well-drained, medium-textured soil. 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.

Varieties and Types

Potato Varieties
Early-Maturing
Caribe - purple-skinned, white-fleshed. Resistant to some common scab and PLRV.
Dark Red Norland - rich dark red skin, white flesh. Tubers round to oblong. Moderately resistant to common scab, stores well.
Irish Cobbler - buff-colored skin, white flesh. Round. Resistant to PVA, moderately resistant to blackleg and Fusarium tuber rot, highly susceptible to PVY and Verticillium wilt.
Satina - attractive yellow skin and flesh. Highly resistant to potato late blight and common scab. Stores well.
Superior - buff-colored skin, white flesh. Oval. Moderately resistant to common scab.
Mid-Season
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. Elliptical to long tubers. Drought tolerant, has high yield potential. Resistant to PVY and PVA, has some resistance to potato late blight and a moderate resistance to blackleg. Susceptible to Verticillium wilt and pinkeye.
Norland - smooth red-skinned, 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-skinned, 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, PLRV, PVA 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.
Yukon Gold - yellowish, buff-colored skin, medium yellow flesh. Resistant to net necrosis and PVA, and has high specific gravity. Storability is excellent with long dormancy.

 

Abbreviations: PVA: potato virus A, PVY: potato virus Y; PLRV: potato leafroll virus

 

Soil Fertility

Lime and fertilizer rates should be applied relative to soil test results and the potato cultivar to be planted. If the cultivar to be raised is common scab resistant, soil pH should be maintained at pH 6.0. This will facilitate not only potato growth but also rotation crops. If the cultivar to be raised is common scab susceptible, then the soil pH should be maintained at pH 5.0 to 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. On most varieties, the amount of nitrogen per acre is usually 140 to 150 pounds. Higher rates can be used on late-maturing varieties such as Russet Burbank and slightly less on 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
POTATO NITROGEN (N)* LBS PER ACRE PHOSPHORUS (P) LBS P2O5 PER ACRE      POTASSIUM (K) LBS K2O PER ACRE
SOIL TEST RESULTS   VERY LOW LOW OPTIMUM ABOVE OPTIMUM VERY LOW LOW OPTIMUM ABOVE OPTIMUM
Where all Fertilizer is Applied at Planting Time                  
Band Placement at Planting 120-180 200 120 30-60 0-30 175 125 100 0-50
TOTAL RECOMMENDED 120-180 200 120 60 0-30 300** 250** 100 0-50
                   
Where Sidedressing is Used                  
Band Placement at Planting 80-120 200 120 30-60 0-30 175 100 50 0-50
Sidedress before plants are 6" high 40-60 0 0 0 0 125 100 50 0
TOTAL RECOMMENDED 120-180 200 120 30-60 0-30 300 200 100 0-50

*SEE PLANT NUTRIENTS FOR INFORMATION ON NUTRIENT MANAGEMENT AND APPLICATION.

**APPLY 125 LB K20/A BROADCAST

Planting 

Plant only certified or foundation seed. Certified and foundation seed 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°F to 40°F with relative humidity maintained at 95%. Seed taken from cold storage should not be planted or cut immediately. Seven to 14 days prior to cutting or planting, tubers should be warmed gradually to 50°F to 55°F. 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 to 2 oz.

Amount (CWT.) of Seed Needed to Plant One Acre

34 INCH ROWS 36 INCH ROWS
INS. BETWEEN SEED IN ROW WT. OF SEED PIECES (OZ.) WT. OF SEED PIECES (OZ) WT. OF SEED PIECES (OZ) INS. BETWEEN SEED IN ROW WT. OF SEED PIECES (OZ) WT OF SEED PIECES (OZ) WT. OF SEED PIECES (OZ)
  1-1/2 1-3/4 2   1-1/2 1-3/4 2
6 29 34 39 6 27 32 37
8 22 25 29 8 20 24 27
10 17 20 23 10 16 19 22
12 14 17 19 12 14 16 18
15 11 14 16 15 11 13 14

The more uniform in size and weight the seed being planted, the more accurate the planter will perform. The ideal seedbed for planting potatoes is warm, medium field capacity in moisture content, and of uniform texture allowing good soil air movement. Soil temperatures should be 50°F to 60°F in order to encourage cut seed wound healing and rapid growth. Do not plant cut seed in soil below 45°F as seed piece decay will be encouraged.

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.

Suggested Seed Spacing

CULTIVAR SPACING IN THE ROW
Kennebec 6" to 8"
Katahdin, Superior, Green Mountain and Irish Cobbler 7" to 10"
Russet Burbank, GoldRush 12" to 16"

Close spacing in the row, 6" to 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" to 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, or the 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 soil-borne diseases such as Rhizoctonia.

Green Sprouting

The practice of pre-sprouting seed potatoes is called green sprouting or chitting. This practice accelerates plant emergence and speeds the development of marketable tubers. Many times it gains the producer as much as 7 to 10 days in having 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. Consumers usually cook the tubers in their skins.

The basic technique is rather simple: About 6 weeks prior to planting, spread the seed tubers in open-top crates, boxes or flats, 1 layer deep with the eyes up. Egg cartons for small seed lots work great. The flats are then kept in a warm place (approximately 70°F.) where light levels are medium 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. Ideally the sprouts will be about 1" in length. Do not cut the seed before green sprouting. Cutting seed pieces prior to green sprouting will encourage desiccation and reduce seed quality.

Cultivation and Hilling

Hilling and cultivation operations are suggested to begin after the plants begin to emerge and should be completed prior to the plants filling half of the row, so as to not cause foliar or root damage. 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 and adverse temperatures. Discs, rolling cultivators, hilling listers 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 some 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. ai Maleic Hydrazide/A to healthy green non-water-stressed potato vines. Apply when most of the tubers of Russet Burbanks are 4 to 6 oz in weight and Round White varieties are 13/4" to 2" in diameter. Apply at least 2 weeks before application of any vine killer. If rain comes within 24 hours of application, effectiveness will be reduced. Do not apply at temperatures above 85°F. 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 chloro-IPC, sold under a variety of trade names, 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. Chloro-IPC is sold as an aerosol treatment to be applied in storage or as an emulsifiable concentrate to be added to wash water for prevention of sprouting in marketing channels. Do not use the herbicide formulation for sprout control. Two other custom-applied materials are also registered.  They are Amplify (di-ispropylnaphtalene) and 1,4 Sight (1,4-dimethylnaphtalene). 

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 insure 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 stolen attachment on tubers.

With chemical desiccation, rates should be reduced if potato plants are stressed.  Please refer to the label of the product being used.

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

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 > endothall (slowest). This implies that the risk of stem end discoloration is greater with paraquat than with the other vine desiccants.

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. Also the products listed here are based on what is currently labeled for use in the state of Maine — these products may or may not be approved for use in other jurisdictions.

carfentrazone (Aim):  3.2 to 5.8 oz/A (7 dh, REI 12h).   Suitable for seed and storage.  A spray adjuvant (NIS, MSO, or COC) is required (1 to 2% v/v).  Thorough coverage is essential.  A second application may be required depending on density of vine growth.  A 7 to 14 day interval is recommended between applications and not more than 11.6 oz/A may be applied in one season.  Minimum spray volume is 20 gal/A.  May be tank mixed or used sequentially with other dessicants (refer to other product labels for restrictions).

diquat (Reglone): 1 to 2 pt/A (7 dh, REI 12h). Suitable for seed and storage. Always use a spray adjuvant (0.1 to 0.5% v/v NIS). Rain fast in 30 minutes. A second application may be made depending on density of vine growth. A 5 day interval is recommended between applications and not more than 4 pt/A may be applied in 1 season. Minimum spray volume of 20 gal/A.

glufosinate-ammonium (Rely): 3 pt/A (9 dh, REI 12h). NOT for seed. This is the same active ingredient as Liberty herbicide. Rainfast in 4 hours. Minimum spray volume of 20 gal/A.

paraquat (Firestorm or Parazone 3SL) is not registered as a vine desiccant for either storage or for seed potatoes.  However, it can be used for Fresh Market Potatoes ONLY: 0.7 to 1.3 pt/A (9 dh, REI 24h). Potatoes must be harvested promptly after desiccation and immediately processed or consumed.  Split applications may be made with a minimum of 5 days between applications.  Do not apply more than 2.6 oz/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.  Rain fast in 30 minutes.  Minimum spray volume is 20 gal/A.  Do not apply to drought-stressed potatoes.  Application to immature potato foliage will not give complete desiccation.

pyraflufen-ethyl (Vida):  2.75 to 5.5 oz/A (7 dh, REI 12h).  Apply when the crop is in the early stages of senescence for best results.  The product may be tank-mixed in sequence with other desiccant products for improved desiccation.  Minimum spray volume is 20 gal/A.  Application may be repeated after 7 days but do not apply more than 11 oz/A in one season.  Rainfast in 1 hour.  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, field 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" to 6" and all equipment surfaces should be padded. If potatoes are harvested at temperatures below 55°F, considerable bruising is likely to occur. If tubers are harvested during hot weather (above 80°F) and they cool off slowly, the likelihood of storage rot is increased. The ideal temperature during harvest is 60°F to 70°F. 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°F to 60°F and adequate through the pile ventilation. This temperature should be provided for 2 to 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 40°F for tablestock or seed or maintained at 50°F 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 handing 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 including quaternary ammonium compounds, (Prosan and Ster-Bac); sodium hypochlorite products (Agclor); and hydrogen dioxide products (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 tuber rot in storage. However, resistant isolates of this pathogen are now common. Preventing cuts and bruises is the best defense against Fusarium. 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.