Crop Production Potatoes

Potatoes Potatoes are the most widely used vegetable in Ireland Potatoes are grown by farmers for two reasons: “Ware potatoes” to be eaten by humans and exported as food “Seed potatoes” to re-plant and grow new potatoes 80% of commercial potato production is concentrated in Meath, Dublin, Donegal, Cork, Wexford and Louth

Potatoes facts Is a root crop Are underground stems called tubers Belong to the family Solanaceae Are perennial plants that grow to a height of approximately 60cm

Categories of Potatoes Potato are classified as: First earlies Second earlies Maincrop First and second earlies are planted in February and are harvested immaturely from May onwards. Maincrop are harvested when they are fully mature in September and October.

1st Earlies 2nd Earlies

Roosters Kerr Pinks

From early February onwards Class Variety Soil Type Sowing Date Harvesting Yield Example 1st Earlies Home Guard Colleen Epicure Sandy From early February onwards From May onwards. Available commercially from May to June 12 – 18 tonnes/ hectare Oval shape, light skin, creamy white flesh. Suitable for boiling, roasting and chipping

2nd Earlies British Queen Orla Carlingford Sandy From mid February onwards From July to September 17 – 25 tonnes/ hectare British Queen. Oval shape, floury white flesh. Suitable for boiling, roasting and chipping

Main Crop Rooster Record Golden Wonder Kerr Pinks Loam pH 5 – 5.5 From March onwards From Aug to Oct. Available commercially from Sep to May 30 – 40 tonnes/ hectare Irregular round shape with distinctive pink skin, deep eyes and white floury flesh Superior in terms of eating and cooking quality

Seed Production For commercial potato production, certified seed must be used Certified seed potato production is centred around Donegal for two reasons: Firstly, cool windy conditions in Donegal keep the aphid population low. Aphids are vectors (carriers) of a number of plant viruses. Secondly, Donegal is isolated from other potato- growing regions in the country, therefore preventing the spread of diseases. Certified seed is also produced by micropropagation.

New seed potatoes New varieties of potatoes are being produced through Teagasc’s Potato Breeding programme in Co. Carlow New varieties are produced form crossing genetically different parents and a trialling process takes place where their characteristics are tested. Each variety is compared under a series of headings. Tuber size Percentage dry matter Processing quality Yield per hectare Susceptibility to blight and other diseases Resistance to eelworm, etc.

New seed potatoes Newly developed varieties include: Cara Orla Colleen Camelot Slaney Cristina

Cultivation Practices Soil suitability: Earlies require sandy soil which contains more air and is easier to heat up. Main crop require well drained loams which holds more moisture in the summer Soil pH between 5.5 and 6. Rotation: Vital to prevent the build up of potato cyst nematode, a soil-borne pest of potatoes. Potatoes should not be grown in the same field more than once every four years. For seed potatoes, once every five years.

Cultivation Practices Preparation of seedbeds and sowing: Potatoes need deep well cultivated soils. Land is ploughed and tilled in preparation for planting. Stones are removed A ridger is used to form drills 80cm apart. Wider drills mean quicker harvesting A potato planter drops the seed down into the soil at least 15cm below the surface to allow for good soil cover. This ensures the tuber is not exposed to sunlight as too much destroys the crop The seeding rate is 2.5 tonnes/hectare Seeds may be sprouted prior to planting.

Preparation of the Seedbed A de-stoner Drill formation

Sprouting Potato seeds are exposed to light so that they develop shoots. This gives the seeds a head start. It is essential when growing earlies. Sprouting speeds up growth and improves yield.

Fertiliser Application Most growers apply a compound fertiliser such as 10:10:20. Commercial growers place the fertiliser in a band either side of the potato drill, so as to promote uniform growth. Excess nitrogen and excess phosphate depresses the dry matter content of potatoes, while the addition of sulfate of potash increases dry matter.

Important elements for potato growth Nitrogen – helps with growth of plant Phosphorous – gives a higher yield Potassium – increases dry matter and improves skin Magnesium – part of chlorophyll for photosynthesis

Weed Control and Earthing Up Deep ploughing in the preparation of the seed bed can eliminate weeds. A residual herbicide should be sprayed before the potato plant emerges. This helps to eliminate annual and soft weeds growing. For perennial weeds, e.g. common cleavers, a contact herbicide is used. Contact herbicides destroy only the plant tissue in contact with the chemical Scotch grass is killed off using a graminicide, e.g. glyphosphate. Once the stems and leaves (haulms) of the potato plant grow, they form a canopy so emerging weeds have no sunlight for photosynthesis and growth.

Earthing up Earthing up has not been practiced in commercial potato production for many years Once potatoes are 20 – 25 cm in height, a ridger is used to widen ridges and deepen furrows so developing potatoes are not over-exposed to light and fungal spores in the air. It also reduces the emergence of weeds by smothering them. Sunlight can cause greening of the tuber where poisonous alkaloids, e.g. solanin, build up Earthing up is also used as a preventative measure against blight. Spores from the leaf find it difficult to attack tubers as additional soil is packed around them With advancement in technology, drills are wider than before so earthing up is not required. Fungicides and herbicides are also used. Organic farmers may still practice earthing up as they don’t spray any chemicals.

Potato Diseases Potato blight Blight is caused by an airborne fungus. Warm humid weather favours the spread of blight. Potato crops should be sprayed every ten days with a fungicide when blight warnings are issued by the Met Office.

Lifecycle of blight Fungal spores can survive the winter in blighted tubers or in the soil Hyphae emerge from these spores and grow between the cells in the leaf of the potato plant. Haustoria (fine branches of hyphae) penetrate the cells of the leaf and absorb food from them. Sporangiophores then develop and grow out through the stomata and produce more spores. Zoospores, with flagellae, swim in a film of water on the leaf and produce a germ tube to penetrate leaf cells and form new hyphae. Rain washes spores into the soil, infecting tubers or they may come in contact with spores at harvesting if infected haulms are not burned off.

Lifecycle continued Blight affects the potato haulms by causing black spot on the upper side of the leaves, while grey mould develops on the bottom during wet conditions. Eventually the whole plant appears black and withered. The tuber displays a brown/purple colour skin with shrunken areas. A rusty brown colour is evident when the potato is cut open

Blight

Prevention of Blight Spray with blight fungicide every 7 to 9 days from May 1st for 1st Earlies, mid May for 2nd Earlies and June 1st for maincrop potatoes This means that 18 to 20 applications of fungicide are made until the end of the growing season. If blight does occur, spray with a curative fungicide, e.g. Curzate – M, twice, four days apart A good rotation will reduce the likelihood of blight as spores will not be present in the soil The use of certified seed ensures blighted seed is not used Chemically burning haulms three weeks prior to harvesting prevents spores being washed onto soil

Potato Diseases Blackleg is a disease caused by bacteria. Cool, wet weather favours the spread of blackleg. It commonly affects the established crop. The disease is spread through contaminated seed.

Pests Wireworms can sometimes be a problem if potatoes are grown after pasture. Slugs can damage tubers especially in wet summers. Aphids are vectors of viral diseases.

Harvest Early varieties are harvested from May onwards. Maincrop is harvested in September and October. The haulms are killed off with a herbicide and the tubers are left for three weeks to allow the skins on the tubers to harden. Potatoes are harvested using an elevator digger.

Storage Potatoes must be stored in purpose-built buildings that are well ventilated, leak proof, insulated and frost proof. Potatoes are often sprayed to prevent sprouting. Commercial farmers store their potatoes in refrigerated units.

Yields First and second earlies yield around 7–10 tonnes per hectare. Maincrop yield between 30 and 40 tonnes per hectare.