Potato

Description

Potato, Solanum tuberosum, is an herbaceous perennial plant in the family Solanaceae which is grown for its edible tubers. The potato plant has a branched stem and alternately arranged leaves consisting of leaflets which are both of unequal size and shape. The leaflets can be oval to oblong in shape and the leaves can reach 10–30 cm (4–12 in) in length and 5–15 cm (2–6 in) wide. The potato plant produces white or blue flowers and yellow-green berries. The potato tubers grow underground and generally located in the top 25 cm (10 in) of the soil. The tubers can range in color from yellow to red or purple depending on the variety. Potato plants can reach in excess of 1 m (3.3 ft) in height and are grown as annual plants, surviving only one growing season. Potato may also be referred to as, spud, Irish potato, white potato or Spanish potato and originates from South America.


Uses

Potato tubers are a staple food source in temperate regions and are eaten after cooking. They may be cut or sliced and made into potato chips or fries. Potatoes can also be processed into starch, alcohol or flour.


Propagation


Requirements
Potatoes are cool season crops which grow best in cooler climates or as a winter crop in areas with warm summers. They are sensitive to heat but can tolerate a light frost. Potatoes require a deep, fertile, loose, well-draining soil with a pH between 5.8 and 6.5 and will grow optimally at daytime temperatures between 18 and 27°C (65–80°F) and night time temperatures between 12 and 18°C (55–65°F). Plants can also be successfully grown outdoors in burlap bags or large containers.

Seed pieces
Potatoes are usually grown from seed potatoes. Small sections of a large tuber known as “seed pieces” or small seed potatoes can be used. Seed potatoes can be purchased from garden centers when in season and through seed companies. Each piece of planting material should have at least two eyes. The eyes are the area from which a shoot will sprout and after cutting should be allowed to cure for a few days prior to planting in the soil. Curing helps to protect the seed pieces from rotting as well as reducing the likelihood of a pathogen invading. Curing is very simple and can be achieved by laying out the seed pieces on paper towels and allowing to dry out for 3 to 4 days.

Planting
Seed potatoes and pieces can be planted 0–2 weeks after the last frost or as soon as the soil is workable in early Spring bearing in mind that the plants will be killed by a frost. Prepare soil for planting by working in compost or well-rotted manure. Potatoes are commonly grown in hilled rows. This involves digging shallow trenches 60–90 cm (2–3 ft) apart after the addition of the compost or manure. Space the seed pieces 30 cm (12 in) apart and cover with 7.5 cm (3 in) of soil. When the plants reach approximately 25 cm (10 in) in height mound the soil up around the stems of the plants so that they are covered up to about half of their height. This protects shallow tubers from turning green from exposure to sunlight. Allow the plants to grow another 25 cm (10 in) and again mound the soil. Continue this process for the duration of the crops growth. Straw can be used around the plants instead of soil which eliminates the need to dig for the tubers but care must be taken to add fresh the straw regularly as it will break down over time.

Alternatively, potatoes can be grown in containers or burlap bags. See: https://www.plantvillage.com/posts/71...

General care
Potatoes are sensitive to soil moisture and grow best when soil moisture is consistent. The plants generally require about 1 inch of water a week from rainfall or irrigation. Water-satureated soil should be avoided as it can poorly formed tubers and rot. In addition, potatoes are heavy feeders and the addition of a balnced fertilizer every two weeks can help increase tuber yields.

Harvesting
The time potato tubers take to reach maturity is variable and depends on the variety being grown, although it is usually about 2–3 weeks after the plants have bloomed. All tubers should be harvested when the vines have died or before a frost which will kill the plants. Harvest the tubers by gently digging them up with a fork or with your hands if the soil is loose enough. Harvesting is easier when the soil is dry. Do not wash the tubers prior to storing.



References

CABI Crop Protection Compendium. (2013). Solanum tuberosum (potato) datasheet. Available at: http://www.cabi.org/cpc/datasheet/50561. [Accessed 31 March 15]. Paid subscription required.

Erhardt, W. H. (2000). Growing potatoes. University of New Hampshire Cooperative Extension. Available at: http://extension.unh.edu/resources/re.... [Accessed 31 March 15]. Free to access.

Rowell, B. (2006). Potatoes. University of Kentucky Cooperative Extension Service. Available at: http://www.uky.edu/Ag/NewCrops/intros.... [Accessed 31 March 15]. Free to access.

Stevenson, W. R., Loria, R., Franc, J. D. & Weingartner, D. P.(Eds.) (2001). Compendium of potato diseases. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.


Common Pests and Diseases

Common scab
Streptomyces spp.

Symptoms
Raised brown lesions on tubers with corky texture; deep, pitted brown or black lesions on tuber with straw-colored translucent tissue underneath
Cause
Bacterium
Comments
Disease is most severe during warm and dry conditions
Management
Common scab can be very difficult to manage and prevention of the disease relies on combining several different methods. These include: avoiding planting infected tubers, using a 3-4 rotation away from potato; planting less susceptible potato varieties (none are immune); maintaining a high soil moisture content for 4-6 weeks after stolon tips begin to swell at the onset of tuber development; amending soil to lower pH and treating seed with appropriate fungicides when available

Blackleg (Soft rot)
Erwinia carotovora

Symptoms
Small, water-soaked lesions on base of stems originating from seed piece; lesions may enlarge to form a large extended lesion stretching from base of stem to canopy; tissue becomes soft and water-soaked and can be lighty brown to inky black in color; wilted, curled leaves which have a soft and slimy texture when wet
Cause
Bacterium
Comments
Bacteria are carried on tubers and in wounds and can be spread to healthy tubers during handling and cutting of seed pieces; disease emergence favors high soil temperatures
Management
Plant seed pieces which are the product of tissue culture; sanitize tools and equipment when cutting seed pieced to prevent bacterial contamination; avoid damaging tubers during harvest; reduce periods of leaf wetness by allowing enough time for leaves to dry throughout the day after watering

Bacterial ring rot
Clavibacter michiganensis

Symptoms
Wilting stems and leaves; dying leaves; lower leaves wilting first; ring of creamy yellow to brown rot visible when tuber is cut crossways
Cause
Bacterium
Comments
Becterium is tuber-borne; bacteria can enter tuber through cutting wounds; disease favored by wet, warm soils; bacteria overwinter in potato debris
Management
Plant only certified seed potatoes - certified seed potatoes are grown in seed beds with zero tolerance of ring rot; remove all crop debris from soil after harvest; sanitize tools and equipment regularly

Verticillium wilt
Verticillium dahliae
Verticillium albo-atrum

Symptoms
Early death of plants; leaflets dying on only one side of the petiole or branching stem; cut through the stem reveals a discoloration of the tissue; discoloration of tubers at stem-end
Cause
Fungi
Comments
Disease emergence favors high temperature and moisture early in season followed by drought; disease can be spread to uninfected fields by wind or movement of infested soil particles
Management
Planting resistant varieties of potato is the most common method of controlling the disease; cultural practices such as using furrow irrigation in place of sprinkler irrigation and avoiding overwatering plant can also reduce the severity of the disease should it occur

Leak
Pythium spp.

Symptoms
Light tan, water soaked area around wound on tuber; internal rotting of tuber which results in internal tissue becomes spongy and possibly developing cavities; dark, watery fluid exudes from the tuber when squeezed
Cause
Fungi
Comments
Disease only affects tubers and fungus can only enter through wounds; all common potato cultivars are susceptible to leak; disease emergence is favored by relatively high temperatures
Management
Rotating crops away from potato and destroying any infected tubers helps to control the disease; infection can be reduced by application of appropriate foliar fungicides; delaying harvest to allow the skin of the tuber to mature reduced the risk of injury to the tuber

Early blight
Alternaria solani

Symptoms
Dark lesions with yellow border which may form concentric rings of raised and sunken tissue on the leaves and stems; lesions initially circular but become angular; leaves become necrotic but remain attached to plant; dark, dry lesions on tubers with leathery or corky texture and watery yellow0green margins
Cause
Fungus
Comments
Disease emergence favors cycles of wet and dry conditions with periods of high humidity and leaf wetness
Management
Application of appropriate protective fungicide can reduce severity of foliar symptoms; reduce stress to plants by fertilizing and watering adequately; plant late varieties which are less susceptible to disease; store tubers in cool environment

Black scurf & Rhizoctonia canker
Rhizoctonia solani

Symptoms
Flat, irregularly shaped black or dark brown fungal fruiting bodies on tuber surface; tubers may be mishapen; red-brown to black sunken lesions on sprouts; lesions may girdle the main stem causing leaves to curl and turn yellow
Cause
Fungus
Comments
Fungus can be spread by infested soil or planting infected seed pieces and tubers; disease emergence favors cool, moist soil
Management
No potato varieties are completely resistant to the disease; control relies on reducing the level of inoculum in both the soil and in tubers; methods include applying fungicide to seed pieces or soil; avoiding planting seeds too deeply in cold soils and rotating crop away from potato to reduce levels of soil inoculum

Black dot
Colletotrichum coccodes

Symptoms
Small black dots (fungal fruiting bodies) on tubers, stolons and stems; roots may rot below ground; leaves may turn yellow and wilt; infection may cause defoliation
Cause
Fungus
Comments
Disease emergence favors poorly draining soil; poor aeration of soil and high temperatures; disease symptoms are most severe in coarse soils that are low in nitrogen
Management
Stressed plants are more susceptible to black dot; rotate crops away from potato; do not plant infested tubers or seed pieces; fertilize and water plants adequately; protective fungicides can be applied where available

Powdery scab
Spongospora subterranea

Symptoms
White to brown galls on the roots and stolon; raised pustules on tuber surrounded by potato skin; shallow depressions on tuber filled with brown spores
Cause
Fungus
Comments
Symptoms all occur below ground
Management
Do not plant tubers showing symptoms of disease; avoid planting potato in poorly draining soils; if disease occurs rotate crop away from potato for a period of 3-10 years and avoid planting tomato

Gray mold
Botrytis cinerea

Symptoms
Flowers covered in gray, fuzzy mold; wedge shaped tan lesions on leaves; a slimy brown rot may be present on stems, originating from the petiole; infected tubers have wrinkly skin and tissue underneath is soft and wet; tubers often develop a gray fuzzy growth
Cause
Fungus
Comments
Disease emergence favors excessive humidity, cool temperatures and shade
Management
Cultural control is very important for managing the disease, provide plants with adequate fertilizer and water; application of appropriate protective fungicides where available can provide adequate control of disease but will not treat an established infection

Wireworms
Aeolus spp.
Anchastus spp.
Melanotus spp.
Limonius spp

Symptoms
Death of seedlings; reduced stand; girdled stems and white heads; wireworm larvae can be found in soil when dug round the stem; larvae are yellow-brown, thin worms with shiny skin
Cause
Insect
Comments
Larval stage can last between 1 and 5 years depending on species
Management
Chemical control impossible in a standing crop, must be applied at preplanting or as a seed treatment; if wireworms are known to be present in soil fallow field during summer and till frequently to reduce numbers; rotate to non-host crop where possible; avoid planting susceptible crops after a wireworm infestation on cereals without either fallowing of applying appropriate pesticide

Colorado potato beetle
Leptinotarsa decemlineata

Symptoms
Feeding damage to foliage; if infestation is severe or if left untreated plants can be completely defoliated; adult insect is a black and yellow striped beetle; larvae are bright red with black heads when they first hatch and change color to pink; larvae have two rows of black spots
Cause
Insect
Comments
Adult beetles emerge in spring; female beetles lay eggs in batches of up to two dozen; eggs are orange-yellow and are laid on undersides of leaves; a female can lay 500 or more eggs over a four to five week period
Management
Control of Colorado potato beetle can be challenging as they have developed high levels of insecticide resistance; in the home garden planting early maturing varieties of potato allows the plants to escape from most damage; adults and larvae should be hand picked from plants and destroyed in soapy water; applications of Bacillus thuringiensis can be effective at controlling larvae but should be applied frequently; some insecticides, including spinosad, are still effective against adult beetles

Aphids (Peach aphid, Potato aphid)
Myzus persicae
Macrosiphon euphorbiae

Symptoms
Small soft bodied insects on underside of leaves and/or stems of plant; usually green or yellow in color, but may be pink, brown, red or black depending on species and host plant; if aphid infestation is heavy it may cause leaves to yellow and/or distorted, necrotic spots on leaves and/or stunted shoots; aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plants
Cause
Insects
Comments
Aphids are most damaging to potato through the transmission of viruses such as Potato leafroll virus; distinguishing aphid features include the presence of cornicles (tubular structures) which project backwards from the body of the aphid; will generally not move very quickly when disturbed
Management
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use

Cutworms
Agrotis spp.
Peridroma saucia
Nephelodes minians
and others

Symptoms
Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits; larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed
Cause
Insects
Comments
Cutworms have a wide host range and attack vegetables including asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato and tomato
Management
Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically

Flea beetles
Epitrix spp.

Symptoms
Small holes or pits in leaves that give the foliage a characteristic “shothole” appearance; young plants and seedlings are particularly susceptible; plant growth may be reduced; if damage is severe the plant may be killed; the pest responsible for the damage is a small (1.5–3.0 mm) dark colored beetle which jumps when disturbed; the beetles are often shiny in appearance
Cause
Insects
Comments
Younger plants are more susceptible to flea beetle damage than older ones; older plants can tolerate infestation; flea beetles may overwinter on nearby weed species, in plant debris or in the soil; insects may go through a second or third generation in one year
Management
In areas where flea beetles are a problem, floating row covers may have to be used prior to the emergence of the beetles to provide a physical barrier to protect young plants; plant seeds early to allow establishment before the beetles become a problem - mature plants are less susceptible to damage; trap crops may provide a measure of control - cruciferous plants are best; application of a thick layer of mulch may help prevent beetles reaching surface; application on diamotecoeus earth or oils such as neem oil are effective control methods for organic growers; application of insecticides containing carbaryl, spinosad, bifenthrin and permethrin can provide adequate control of beetles for up to a week but will need reapplied

Late blight
Phytophthora infestans

Symptoms
Irregularly shaped spreading brown lesions on leaves with distinctive white fluffy sporulation at lesion margins on the underside of the leaf in wet conditions. In dry condition the lesions dry up and go dark brown with collapsed tissue; water-soaked dark green to brown lesions on stems also with characteristic white sporulation; later in infection leaves and petioles completely rotted; severely affected plants may have an slightly sweet distinctive odor; red-brown firm lesions on tubers extending several centimeters into tissue; lesions may be slightly sunken in appearance and often lead to secondary bacterial rots.
Cause
Oomycete
Comments
The pathogen can survive for several months to years in the soil; emergence of disease favored by moist, cool conditions; major cause of disease spread is infected tubers
Management
Control depends on a multifaceted approach with importance of certain practices changing based on geographic location: destroy infected tubers; destroy any volunteer plants; application of appropriate fungicide to potato hills at emergence; time watering to reduce periods of leaf wetness e.g. water early to allow plant to dry off during the day; plant resistant varieties; apply appropriate protective fungicide if disease is forecast in area

Pink rot
Phytophthora erythroseptica

Symptoms
Stunted plant growth; wilting leaves; dying leaves; marked tuber decay; dark brown eyes on tuber; cut tuber turns pink after 20-30 min air exposure, then turns brown and finally black
Cause
Oomycete
Comments
Disease emergence favors high soil water saturation late in the season
Management
Plant potato in well-draining soils with no history of pink rot; avoid overwatering plants; avoid wounding during harvest

Potato leaf roll
Potato leafroll virus (PLRV)

Symptoms
Young leaves rolled and yellow or pink; lower leaves have leathery texture and roll upward; necrotic netting in vascular tissue of tuber may be present; plant exhibits an upright growth habit and growth may be stunted
Cause
Virus
Comments
Transmitted by several species of aphid; infected seed tubers and volunteer potato plants provide a source of inoculum for the virus
Management
Grow plants produced clonally from PLRV-free stock; harvest potato crop early in temperate regions to avoid aphid migrations late in season; remove and destroy infected plants and tubers; application of appropriate insecticides where available may help reduce spread

Potato virus A
Potato virus A (PVA)

Symptoms
Mild mosaic pattern or mottling on leaves; severely infected plants may have alternating patches of yellow and dark green tissue; leaves may have a shiny appearance; stems bending outwards slightly
Cause
Virus
Comments
Virus is transmitted by several species of aphid and can be transmitted to the next potato generation by planting infected tubers; tubers show no visible symptoms
Management
Plant material which is free of PVA; plant tolerant potato varieties in areas where virus is common; application of appropriate systemic insecticides helps to control aphid populations`

Potato virus X
Potato virus X (PVX)

Symptoms
Mild mosaic pattern on leaves; severely infected plants may be dwarved with smaller leaves; necrosis of plant tops and tubers may occur
Cause
Virus
Comments
PVX can be transmitted by infected leaves coming into contact with healthy ones
Management
Planting seed free of PVX is the most important method of controlling the virus

Potato virus Y
Potato virus Y (PVY)

Symptoms
Symptoms vary widely from mild mosaic of leaves to leaf necrosis and plant death depending on the variety of potato and the strain of the virus: leaves may turn yellow and drop from plant; symptoms may be present on only one shoot of the plant; plants with severe leaf necrosis may produce tubers with light brown rings on the skin
Cause
Virus
Comments
Virus is transmitted by more than 25 different species of aphid; virus can be transmitted over long distances by aphids; can be transmitted mechanically by contact with infected leaves or tubers
Management
Plant only certified seed potatoes; application of appropriate systemic insecticides, where available, may control spread of virus within a single plantation but will not prevent spread caused by winged aphids; remove and destroy symptomatic plants; plant resistant varieties