Potatoes:Guidelines
GUIDELINES: POTATO PRODUCTION
Contents
STATISTICS
OUTLINE OF MANAGEMENT ACTIVITIES
Cultural Practices
_____ If field has not been planted with potatoes for two to three previous years, field should be evaluated with an appropriate soil test for nutrient status and a pH. _____ Test for organic matter status every three years. _____ Fertilizer should be applied in accordance with soil test results and expected uptake of nutrients. _____ Account for additional nitrogen supplied by organic matter, compost, manure and cover crops. _____ Determine from Cooperative Extension or seed supplier the expected nutrient uptake. _____ Nitrogen fertilizer should be applied by split application (some applied at planting and some applied as a sidedress). _____ Apply compost or manure (calculate nitrogen contribution) and adjust fertilizer application accordingly. _____ Winter cover crops are preferred and should be a legume or legume/grass mix. _____ Calculate the nitrogen contribution of the cover crop and adjust fertilizer application appropriately. _____ Keep an experimental plot to test reduced rates of fertilizer. Record the results.
Pesticide Management
_____ Use approved and registered pesticides according to label. _____ Maintain application records including date, location, applicator, target pest, pesticide name, EPA registration number, formulation, rate and number of acres treated are maintained. _____ All sprayers are calibrated at the start of the season. _____ Minimize pesticide drift. _____ Develop and implement a resistance management plan. _____ Select pesticides which will preserve natural enemies of pests. _____ Use separate sprayers for herbicides and insecticides. _____ Check sprayer(s) calibration at least once during the season and recalibrate each sprayer as needed. _____ Maintain records of planting dates for treated fields. _____ Keep records of stage of crop of treated field. _____ Use water-sensitive spray cards to test coverage of leaf surfaces.
Insect Pest Management
_____ Monitor colorado potato beetle (CPB) densities weekly. _____ Scout "SUSPECT INSECTS" .. Aphids .. Cutworms .. Colorado Potato Beetle .. Flea Beetles .. Leafhopper .. Potato Psyllid .. Potato Tuberworm .. Silverleaf Whitefly .. Wireworms _____ Scout 25 to 50 plants per field. _____ Correspond application of insecticides for CPB to action thresholds as specified in Cooperative Extension recommendations. _____ Manage insecticide resistance by not using the same synthetic insecticide more than once per season or by not using the same synthetic insecticide on the same generation of the CPB. _____ If imidacloprid is used on the whole-field, soil-applied systemic (Admire) application is limited to non-rotated fields and is applied no more than once every two years in the same field. _____ If imidacloprid is used on foliar application, (Provado) is limited to one generation of CPB (overwintered or summer adults) per season or soil application is made as a border (15-20 rows) in non-rotated fields or adjacent to fields previously planted with potato. _____ If imidacloprid is used on soil application, foliar application should not be made in the same year. _____ Microbial insecticides (such as Bt) should be used for at least half of the insecticide applications for control of CPB. _____ If Bt is used, egg masses are flagged at the beginning of each CPB generation to determine egg hatch and proper timing of microbial insecticides. _____ Use other non-chemical control methods of Colorado potato beetle (i.e. propane flaming, delayed planting, or disruption of movement from overwintering sites). _____ Monitor aphid densities. _____ Identify aphid species. _____ Select which insecticide will best control the species present. _____ Correspond insecticide application for aphids to action thresholds as specified in Cooperative Extension recommendations. _____ Monitor potato leafhopper densities. _____ Correspond insecticide application for potato leafhopper to action thresholds as specified in Cooperative Extension recommendations. _____ Apply half rates of banded granular insecticides at hilling.
Disease Pest Management
_____ Use certified virus-free seed. _____ Practice proper sanitation by disposing properly of cull piles and by removing volunteer potato plants. _____ Monitor weather and crop conditions for fungicide application intervals. _____ Monitor fields for diseases including late blight. Record the results.
Weed Pest Management
_____ Scout "SUSPECT WEEDS" .. barnyardgrass (Echinochloa crus-galli) .. bindweed, field (Convolvulus arvensis) .. bluegrass, annual (Poa annua) .. buckwheat, wild (Polygonum convolvulus) .. cudweed (Gnaphalium sp.) .. dodder (Cuscuta spp.) .. fiddleneck, coast (Amsinckia menziesii var. intermedia) .. foxtails (Setaria spp.) .. knotweed, common (Polygonum arenastrum) .. lambsquarters, common (Chenopodium album) .. mustards (Brassica and Sinapis spp.) .. nettle, stinging (Urtica urens) .. nightshade, black (Solanum nigrum) .. nightshade, hairy (Solanum sarrachoides) .. nutsedge, purple (Cyperus rotundus) .. nutsedge, yellow (Cyperus spp.) .. oat, wild (Avena fatua) .. pigweeds (Amaranthus spp.) .. puncturevine (Tribulus terrestris) .. purslane, common (Portulaca oleracea) .. quackgrass (Elytrigia repens) .. radish, wild (Raphanus raphanistrum) .. rocket, London (Sisymbrium irio) .. sandburs (Cenchrus spp.) .. shepherd's-purse (Capsella bursa-pastoris) .. thistle, Canada (Cirsium arvense) .. thistle, Russian (Salsola tragus) .. witchgrass (Panicum capillare)
_____ Scout fields mid to late season for the following years preparation. _____ Note identification and location of weeds. _____ Use previous season's weed survey to determine herbicide selection and rate. _____ Use cultivation and banded application of herbicides to reduce herbicide use. _____ Delay application until crop emergence. _____ Use an experimental plot to test different weed management techniques.
Weather and Crop Monitoring
_____ Monitor weather and crop parameters _____ Keep daily records. Date: Min/max temperatures: Rainfall: Hours of leaf wetness: Stage of tree development (by cultivar, weekly):
CHECKLIST OF MANAGEMENT ACTIVITIES
Previous Crop
Pest Complex: Seed Tubers _____Visit seed production areas to observe seed fields. _____Mature seed crop with use of vine killing agents or vine removal if necessary. _____Harvest seed tubers with minimum mechanical damage. _____Harvest seed tubers before exposure to freezing temperatures.
Pest Complex: Insects and related pests _____Destroy weed host sources. _____Use Rotations that suppress potato insects.
Pest Complex: Diseases _____Destroy weed hosts. _____Destroy potato volunteers. _____Use rotations that suppress potato pathogens.
Pest Complex: Nematodes _____Use rotations that suppress problem species of nematodes.
Pest Complex: Weeds _____Use rotations that allow control of problem weeds. _____Avoid herbicides that leave residues harmful to potatoes the following year.
Between Crops
Pest Complex: Seed tubers _____Store seed tubers in proper environment.
Pest Complex: Insects and related pests _____Destroy weed host sources. _____Monitor for wireworms.
Pest Complex: Diseases _____Eliminate cull piles. _____Destroy potato volunteers. _____Use soil fumigation when necessary and feasible.
Pest Complex: Physiological disorders _____Analyze for soil fertility, chemistry, and physical constraints.
Pest Complex: Nematodes _____Use tillage to destroy crop residues. _____Analyze soil for nematode species. _____Use fall fumigation when necessary and feasible.
Pest Complex: Weeds _____Use tillage and herbicides to control perennials and potato volunteers. _____Allow breakdown of harmful herbicide residues.
Preplanting
Pest Complex: Insects and related pests _____Control weed hosts. _____Use soil-applied insecticides when necessary.
Pest Complex: Diseases _____Use highest quality certified seed tubers. _____Suberize cut seed or plant immediately after cutting. _____Use seed treatment fungicides when necessary. _____Provide proper planting conditions: Correct soil structure; Soil temperature above 45°F (7°C) _____Establish soil moisture that will remain adequate until emergence.
Pest Complex: Physiological disorders _____Store seed tubers and cut seed properly. _____Obtain desirable seed piece size. _____Provide proper planting conditions.
At Planting
Pest Complex: Insects and related pests _____Use systemic insecticides properly when necessary.
Pest Complex: Diseases
_____Use good sanitation during seed cutting and planting. _____Sample and monitor for diseased seed pieces. _____Plant at correct depth in warm (above 45°F [7°C]), moist soil.
Pest Complex: Physiological disorders _____Provide proper soil fertility. _____Plant at correct depth and spacing.
Pest Complex: Nematodes _____Use nematicides if necessary.
Preemergence
Pest Complex: Diseases _____Avoid preemergence irrigations. _____Plant shallow to hasten emergence; form hills after emergence.
Pest Complex: Weeds _____Apply preemergence herbicides when necessary.
Emergence to Tuber Growth
Pest Complex: Insects and related pests _____Monitor for insects and mites. _____Destroy volunteer host sources. _____Hill to prevent exposure of tubers to pests. _____Apply pesticides when necessary.
Pest Complex: Diseases _____Maintain proper soil moisture and fertility. _____Avoid extended periods of wet foliage. _____Monitor for disease development. _____Apply fungicides when necessary.
Pest Complex: Physiological disorders _____Maintain proper soil moisture and fertility. _____Hill to prevent exposure of tubers to heat and light.
Pest Complex: Weeds _____Monitor for weed emergence. _____Time hilling to control emerging weeds. _____Apply postemergence herbicides when necessary.
Maturation and Harvest
Pest Complex: Insects and related pests _____Keep tubers covered to avoid tuberworm damage. _____Use early vinekill to avoid aphids and frost.
Pest Complex: Diseases _____Maintain proper soil moisture. _____Apply foliar fungicides or vine killing agents when necessary for late blight control. _____Harvest after complete vine death to reduce late blight infections. _____Use careful harvesting and handling procedures. _____Harvest at proper soil moisture and temperature. _____Maximize soil removal before storage.
Pest Complex: Nematodes _____Time harvest to avoid tuber damage when possible. _____Isolate lots with infested tubers.
Pest Complex: Weeds _____Apply contact herbicides for complete vinekill and control of nutsedge. _____Manage water for late-season weed control.
Storage
Pest Complex: Diseases _____Use proper sanitation in storage areas. _____Use proper cutting conditions. _____Use ventilation to hasten drying or wet tubers. _____Maintain proper ventilation, humidity, and temperature. _____Monitor storages for disease development.
Pest Complex: Physiological disorders _____Maintain proper ventilation, humidity, and temperature.
Pest Complex: Nematodes _____Monitor tubers going into and coming out of storage for symptoms of nematode damage. _____Store at temperatures that prevent nematode multiplication if compatible with intended use.
POTATO DEVELOPMENT=
Potatoes have four growth stages, which include the vegetative stage, tuber initiation, tuber growth, and maturation. Cultivars will influence the growing practices as well as how seeds respond to weather, cultural practices, pest damage, and other factors.
Vegetative Growth
Tubers grow because of starch in the seed piece that supplies energy for sprout growth and development. The root system is highly branched and is concentrated in the top 18 inches of soil. Stolons are lateral shoots that develop from buds at the underground nodes of stems and contains a large amount of phloem tissue to transport the nutrients from the stems to the tubers. Tubers can be classified as determinate or indeterminate depending on their growth pattern. Indeterminate plants have a vine type growth habit and complete their growth cycle in at least 100 days. Determinate plants have a bush type of growth habit and require 60-80 days to complete their growth cycle.
Potato plant morphology (H. F. Schwartz; Colorado State University)
Potato plant morphology (H. F. Schwartz; Colorado State University)
Potato plant morphology (H. F. Schwartz; Colorado State University)
Tuber Initiation
Tuber initiation begins after the plant produces enough carbohydrates to support the growth of leaves, stems, and roots and the excess goes to the tuber. Tuber initiation is affected by soil moisture, soil temperature, and nitrogen management. Tubers usually first appear on the lower, older stolons, when high amounts of sucrose begin to build up in the stolon tips where there is rapid cell division. The length of the initiation period varies among cultivars.
Tuber Growth
Tubers are modified stems that carry all the necessary parts for new tuber production. Each tuber contains eyes that have several buds, which can give rise to new stems. The tuber skin is made up of several layers of sloughed off corky cells that protect the tuber. If the tuber becomes injured, the epidermis forms a waxy substance called suberin that acts as a barrier to invasion by disease organisms. Lenticels are surface pores that are found on both stems and tubers and serve as sites for gas exchange. The layers of suberin are found under the lenticels but prevent infection from entering the tuber.
Maturation
As the tubers begin to reach maturity, several physical changes happen to the plant. The skin on the tuber begins to thicken, the dry matter content reaches a maximum, and the vines begin to turn yellow and lose leaves due to slowed photosynthetic activity. During this time the eyes become dormant and starch synthesis gradually stops as the vines die.
Water and Nutrient Transport
Nutrients and water move from plant roots to the leaves and stems through xylem tissue within the vascular system. This transport can be restricted by certain pathogens causing the vines to wilt or age prematurely.
Carbohydrate Transport
Several diseases may reduce or block the transport of carbohydrates from foliage to tubers by clogging the phloem tissues of the vascular system. Sucrose also builds up in the leaves causing them to become brittle and they can take on a reddish color.
Foliage Reduction
Some pests can reduce the leaf area available to produce photosynthesis and this causes the tubers to become smaller as well as early aging of vines that are trying to support the growing tubers.
Second Growth
It is important that the plant does not experience water stress because this can affect the carbohydrate buildup in the tuber. When conditions for photosynthesis are again favorable after a period of stress, the tubers may resume growth, some slower than others, but often it is uneven growth. When this occurs, various typed of tuber malformations occur causing them to be unacceptable for processing.
REQUIREMENTS
Soils
Potatoes grow best in sandy, gravelly, shale loams that are well drained, well aerated, and well supplied with organic matter.
Temperature
Potatoes are cool weather crops and should be grown under conditions where the average day temperature is less than 70°F. Cool nights are important for the tuber solids to develop.
Moisture
The potato plant contains about 80% water and must maintain adequate soil moisture to avoid cracking, knobby, or hollow tubers. Potatoes do not have a very extensive root system which means that nutrient uptake is often inefficient. Most of a root system is only in the top two feet of the soil and since much of the nutrients get leached out from irrigations, nutrients must be applied regularly.
Nutrient Requirements
Most fertilizer programs need multiple applications because the nutrients rest so close to the soil surface. Starter fertilizers are usually high in phosphorus and additional fertilizers are high in nitrogen. Additional applications of nitrogen may be applied as a side dress fertilizer or though the irrigation water. Heavier soil will require more frequent, supplemental applications.
CULTURAL PRACTICES
Careful water management helps prevent early seed decay. Excess fertilization may reduce yields, and inadequate fertilization may also reduce yields and encourage some diseases.
PLANTING
Before planting, proper field preparation is essential for maximum quality and yield. It is important to eliminate all old residues that may be left in the field from previous crops because they can be hosts of several pathogens. The soil should be plowed 8-12 inches deep and the soil moisture should be 60-80% of field capacity at planting. Always use a preplant irrigation if the soil is too dry because it is best to avoid irrigating again until after the seeds have emerged. The soil temperature should be at least 45°F (7°C) before planting and this will help keep the soil moisture levels high. The width of the rows and the depth of planting varies according to the area, time of year, cultivar, and conditions at planting. Many seeds are planted 4-6 inches deep in rows that are 30-36 inches wide.
Hilling
Hilling should always be done after the plants begin to emerge, and not beforehand. There are many different equipment options to perform the hilling operations. Hilling should not expose any tubers as this will cause them to develop a green color with a bitter taste. The hills should be flat and broad for best results. Cultivation during hilling destroys emerged weeds, and some soil-applied herbicides can be mixed in at this time. Plan to complete hilling before plants are so large that pruning of stolons or roots may occur.
Frost Protection
Irrigation water can be used to keep the plants from freezing and often sprinklers are used. The advantage of sprinklers is that they can be turned on before the air temperature drops below freezing and left on until the air temperature has risen again.
SEED QUALITY
A number of pests can be transmitted in infected seed tubers, however, stem cutting and micropropagation techniques have been developed to obtain pest-free potato plants for propagation and production of certified seed tubers. Certified seed show very low percentages of pest and disorder symptoms during inspections made by the state's seed certification program. In fields where seed potatoes are grown, extra precautions are made against diseases and other pests. It is extremely important to clean all the equipment between fields and keep the mechanical contact to a minimum to reduce the spread of pathogens. In addition, follow careful handling of the seeds to keep the seeds from becoming infected. Potato seed should always be purchased from a reputable supplier of good quality, certified seed.
Resistant Cultivars
The term resistant cultivar refers to a plant that is infected by a disease organism but is unaffected or has no measurable effect on yield or quality. Tubers require a certain amount of aging to break dormancy of enough eyes so that each seed piece will produce two or three stems. The tubers should be stored at a temperature of 35° to 38°F (1.7° to 3.3°C) and then approximately 2 weeks before cutting, warm seed tubers gradually to 50° to 55°F (10° to 13°C) and hold them at that temperature with a relative humidity greater than 90% and good ventilation. The seed pieces should be planted immediately in moist soil. This encourages wound healing when they are cut and greatly reduces the incidence of seed piece decay after planting. Most areas prefer to have seed pieces that are 11/2 to 2 ounces for optimum performance.
Seed Treatment
Chemical seed treatments are often needed to fight against fungus development on seed pieces. To avoid treatments, good quality seed tubers must be used, soil moisture must be optimal, and field conditions must favor rapid wound healing and emergence.
FERTILIZATION
It is important that the proper amount of fertilizer be applied because if nutrient deficiencies occur, the plants send all the nutrients from the stems and leaves to the tubers causing early aging of the vines. If the plants receive excess fertilizer, the onset of tuber growth can be delayed and there may be in increase in decay after harvest. Nitrogen is the nutrient that is most often needed, but phosphorus and potassium are usually needed as well. In order to determine how much fertilizer to apply, it is helpful to know what crops have previously been grown in the field and how much of individual nutrients were applied. Tubers maximize fertilizer treatments during early and middle growth, when the plants most need them. Most nutrients can be applied either as a preplant broadcast or in a band close to the seed. Most nutrients are not easily leached from the soil and sufficient quantities can be applied before planting to last all season. Nitrogen is the exception because it is easily leached from the root zone and may need several applications during the growing season. The final application of nitrogen should not be any later than four weeks before vinekill because it encourages too much top growth. Having the soil tested at a laboratory before planting is the best way of determining how much fertilizer to apply. However, in order to determine the nutrient status in the crop, a petiole analysis is the best way of assessing this information. The best fertilizer programs include each of the following steps: 1) have the soil and plant tissue tested for nutrient analysis, 2) use a band placement fertilizer of nitrogen, phosphorus, and potassium near the seed at planting, 3) use an early season sidedressing of a complete fertilizer, and 4) make nitrogen applications as frequent as petiole tests indicate they are necessary.
IRRIGATION
The amount of water the plant receives is extremely critical to the development of the tuber. Too little water will reduce yields, induce tuber malformations, or increase severity of diseases. Excess or poorly timed irrigation may reduce yields and quality, cause several disease problems in the field or in storage, or leach nutrients from the root zone. Potatoes should be irrigated when the soil reaches a depletion level of 30-40% so that the plant does not experience water stress. Because the root system in potatoes is rather shallow, mostly in the top 12-18 inches, the plants must be watered more frequently than many other crops.
Irrigation Methods
There are several different methods of irrigating potatoes, but the most commonly used methods are center pivots, wheel lines, and solid set sprinklers. Sprinklers offer a greater flexibility than furrow irrigation because they distribute the water more evenly, fertilizers and pesticides can be mixed with the water, and they can adapt to uneven ground. When the slope of the land is less than 2% then furrow irrigation can effectively be used. The rows must be shorter for furrow irrigation and fertilizer is not recommended to be mixed with the water because it is difficult to get an even distribution.
Preirrigation
The soil moisture should be at 60-80% of field capacity at planting time and this usually requires one or two preirrigation treatments. It is important that the land not be irrigated between planting and the emergence of the plants as this will increase the possibility of diseases and seed decay.
Post plant Irrigations
After the plants have emerged, they should be irrigated once the soil moisture is 30-40% depleted. Because potatoes have a relatively short root system, only the top 18 inches of soil need to be brought back to field capacity. Later in the season when harvest approaches, the soil moisture should be at about 60% field capacity when the vines are killed. This allows the skins on the tuber to thicken and withstand bruising during harvest.
Scheduling
In order to develop a reliable water schedule, it is necessary to know what the soil texture is because sandy soils will require more water than loamy soils and will show signs of water stress earlier. Always check the soil moisture before applying more water so that water reaches to proper rooting depth. Tensiometers, neutron probes, and aerial infrared photography are all ways to measure soil moisture and identify problem areas. Water budgets are also a way of estimating how much water the plants require from day to day. However, not all water is lost just through the roots, a considerable amount is lost due to transpiration, through the leaves. Water useage will vary from field to field. Disease, weeds, insects, and management factors are all taken into consideration of the amount of water needed for a crop. A good irrigation program will include the following items: starting the soil at field capacity, monitoring the soil moisture, recording daily evapotranspiration levels, keeping records of rainfall, irrigating between 18-24 inches below the soil surface, and using an irrigation system that will allow uniform water distribution.
Managing Salinity
All soil should have a routine analysis in a laboratory before planting to determine salinity problems, as well as potential nutrient deficiencies. Salts greatly influence the irrigation water required. If the salt concentration is high, plants will be able to withdraw less water and a smaller amount of water will be available to the plant.
HARVEST
Careful handling should be an important consideration during harvest because a large percentage of harvested potatoes will go directly to a storage facility where bruising will deteriorate the tuber. Potatoes can also go directly to a packinghouse or to a processor from the field.
Potato topping (H. F. Schwartz; Colorado State University)
Potato topping (H. F. Schwartz; Colorado State University)
Potato topping (H. F. Schwartz; Colorado State University)
Soil Moisture
Proper soil moisture and temperature are both important factors that can reduce bruising. If the water content in the tuber is too low, the tubers are extremely sensitive to bruising and if the water content is too high, they are sensitive to blackspot bruise. Soil moisture of 60% to 80% of field capacity is generally recommended.
Temperature
The tubers will perform better and be less susceptible to shatter bruising if the soil temperature does not fall below 50°F (10°C). Because of the increased chance of bruising, it is recommended to harvest the potatoes when the soil temperature is above 50°F, usually during the daytime hours.
Vine Killing
Most potatoes are harvested after the vines have died which allows tubers to mature and develop a thicker skin making them less susceptible to bruising and diseases. In additions, tuber sugars reach a more desirable level and some diseases do not affect dried up vines. To increase the effectiveness of vine-killing treatments, avoid using chemical vine killers during cool, wet weather, avoid exposing or damaging tubers during mechanical operations, make sure the soil moisture is adequate (at least 50% of field capacity), and begin vine kill about about 2-3 weeks before harvest to avoid unnecessary tuber discoloration.
Spraying potato vines with gramoxone (H. F. Schwartz; Colorado State University)
Burning potato vines (H. F. Schwartz; Colorado State University)
Equipment Operation
The condition of the equipment will have a great impact on the success of the harvest. Make sure that all equipment is in good repair, correctly adjusted, and run by an experienced operator. To reduce bruise injury, important considerations are the digger blade depth and losses at the blade, reducing the amount of spill-out, apron pitch, travel speed, and drop heights. Keep the chains filled so the tubers have little space to bounce around and use padding on equipment wherever bruising might occur.
Sprout Inhibitors
Sprout inhibitors should be applied to fresh market or processing potato tubers if they are going to be stored for more than 2 or 3 months. There are two types of inhibitors that are used, maleic hydrazide that is applied during the actively growing stages and chlorpropham (CIPC) that is applied through the ventilation system while the tubers are in storage. Maleic hydrazide must be applied when the tubers are 11/2 to 2 inches in diameter or when the lower leaves are turning yellow. Chlorpropham (CIPC) must be applied in a well ventilated storage facility and can be applied either as an aerosol spray or through the ventilation system.
Storage
All storage facilities should have controls for temperature, humidity, and proper ventilation to remove field heat, excess moisture that may condense on colder tubers, and carbon dioxide produced by respiration.
Curing
Tubers need to be stored at different temperatures depending on their outcome. During the first part of storage, all tubers can be stored at a temperature of 50° to 55°F (10° to 13°C) with relative humidity above 95% which helps cure small scrapes in the skin and prevents decay. Tubers for french fries or fresh market should be cured at a temperature of 45°F (7.3°C) and 50°F (10°C) for chipping cultivars. The tubers should be dried and cooled as quickly as possible with high flows of nonhumidified air.
Holding
Tubers should be stored at different temperatures depending on how they will be used. The following holding temperatures are recommended: tubers for chipping, 50° to 55°F (10° to 13°C), french fries, 45° to 50°F (7.3° to 10°C), fresh market, 40° to 45°F (4.4° to 7.3°C), and seeds, 35° to 40°F (1.7° to 4.4°C). Although the temperatures are relatively low, the humidity should remain high to avoid pressure bruising.
Warming
When removing tubers from storage, their temperatures should be above 50°F (10°C), but it is recommended to allow the heat of respiration to warm tubers rather than using warm air and maintain high humidity levels. If excessive sugars have accumulated in tubers to be used for processing, warming above 50°F for 3 weeks may reduce their sugar to acceptable levels.
Sugar Accumulation
Sugar accumulation is undesirable in tubers used for processing because it causes the product to darken and so storage temperatures are critical for converting the sugars to starch. Tubers that are going to be used for chips usually are stored at no less than 50°F (10°C), and tubers used for french fries no less than 45°F (7°C).
Dormancy
The dormancy period is the time required for the eyes to sprout after the seeds have been harvested. Initially only the apical eye will sprout because it is dominant over the other eyes, but over time, the apical dominance weakens and all eyes will sprout. Tuber seeds should be stored at a temperature of about 35° to 38°F (1.7° to 3.3°C) to delay sprouting.
AGING <CF 000 100 000><S18>Aging
When seeds are placed in storage, sometimes physiological aging occurs which means that dormancy and apical dominance are often lost. This can be beneficial because it encourages the other eyes on the seed to sprout creating more stems per hill that will set more tubers.
Pest Activity
Regularly check the field for the invasion of possible pests or every 2-3 days after they are discovered. Some pests will require longer and more extensive treatments for control than others. However, good control will keep pests down as well as eliminate excessive traffic through the field to control the diseases. In many cases, some diseases can be spotted early in the season before the tubers are too large and control can be easier.
Soil, Water, and Tissue Testing
It is important that the soil and water be tested in a professional laboratory to determine fertilizer requirements and predict possible hazards to the plants. The tests should determine the amount of salt in the soil and water, sodium and boron levels, and also measure the level of nitrates. Having the plant tissues analyzed during the growing season is the best way to determine the crop nutrient status.
ROTATION
Crop rotation is an economical way of increasing soil fertility and organic matter, improving the soil structure, controlling certain pests, and conserving soil moisture. The crops that are most commonly used in rotation with potatoes are forage crops and grains and corn. In some areas, alfalfa, cotton, sugar beets, and beans have been used.
SANITATION
There are a few sanitation practices that can be used to prevent infesting the soil with additional diseases or pests. The following is a list of items that should always be practiced. Use the highest quality certified seed tubers to reduce the risk of bringing in diseases with the seed. Always clean the seed cutting equipment and all equipment between fields. Do not irrigate with tailwater that may contain contaminants or harmful herbicides. Install screens at canals or ditches to filter out unwanted seeds in the irrigation water. Destroy all residues from previous crops. Control weeds with herbicides and destroy all weed stands along the field borders.
PESTICIDES
Caution should be used when using pesticides to not harm natural enemies or crop plants. Always read the label before application and make sure that the treatment applied is suited to the appropriate stage of the target pest. Reducing treatments needed for control will cut costs and potential hazards. Contact a local farm advisor about the resistance that some pests have to pesticides in certain areas. It may be necessary to change pesticides or control measures.
MISC. PHOTOS=
Potato field (H. F. Schwartz; Colorado State University)
Potato field flowering (H. F. Schwartz; Colorado State University)
Potato field scouting (Larry Duell) (H. F. Schwartz; Colorado State University)
