Potato
Crop Atlas · Vegetables
A complete field reference for potato, written for the export and processing crops of Egypt and the region. It covers the growth stages that decide tuber number and tuber size, a nutrient programme built around the crop’s exceptional potassium demand, the physiological disorders that cost grade rather than yield, and the diseases, pests and nematodes that decide whether a consignment ships at all.
Key takeaways
- Potato takes up more potassium than nitrogen, often by half as much again. A programme balanced like a cereal programme will leave yield and tuber size on the table.
- Tuber number is fixed in a short window a few weeks after emergence, and nothing later in the season recovers it. Everything after that only fills the tubers already set.
- Brown rot is the single biggest commercial risk for Egyptian potato exports, and it is managed by zone certification, clean seed and water hygiene, not by chemistry.
- Potato is shallow rooted and sensitive to both drought and waterlogging. Steady soil moisture prevents second growth, growth cracks and common scab at the same time.
- For processing, specific gravity and reducing sugars decide acceptance. Both are driven by variety, by potassium and nitrogen balance, and by storage temperature.
Production: world and Egypt
Potato (Solanum tuberosum) is the world’s largest non-cereal food crop, with global production of roughly 375 million tonnes per year from about 16.8 million hectares. China is by far the largest producer at close to 95 million tonnes, followed by India at around 57 million tonnes, then the United States, Germany and Bangladesh.
Egypt produces approximately 6.9 to 7 million tonnes per year, which makes it Africa’s leading potato producer and one of the world’s largest exporters of fresh ware potatoes, shipping over 1.3 million tonnes. Potato is Egypt’s second-largest agricultural export after citrus. The main destinations are Russia, the European Union, the United Kingdom and the Gulf states, with Southeast Asian markets growing.
Production is concentrated in the Nile Delta, in Beheira, Menoufia, Sharqia, Dakahlia and Gharbia, in Middle Egypt, and increasingly in the reclaimed desert areas of Nubaria and Wadi El-Natrun under centre pivot and drip. The main export window runs from January to June, extended towards October out of cold storage, which is the structural advantage of the Egyptian crop: it arrives when northern hemisphere supply is at its thinnest.
Types and growing systems
Market types
- Ware or table potatoes: sold fresh, graded on size, shape and skin finish. Spunta and Cara dominate the Egyptian fresh export crop.
- Crisping varieties: round tubers with high specific gravity and very low reducing sugars, so the crisp fries pale rather than brown. Lady Rosetta and Hermes are the common types.
- French fry varieties: long tubers with high dry matter and a long enough shape to give a high yield of full-length fries. Agria is the standard example.
- Seed potatoes: a separate production system under strict certification, with far tighter virus and bacterial tolerances than any ware crop.
Seed
Potato is propagated vegetatively, which means every disease in the seed is planted with it. This is why certified seed is not an optional upgrade: virus, blackleg, black scurf and brown rot all travel in tubers. Typical seed rates are 2.5 to 3.5 t/ha depending on seed size and target tuber number, planted 25 to 35 cm apart in rows 75 to 90 cm wide.
Physiological age of the seed matters as much as its health. Well-sprouted, correctly chitted seed emerges fast and evenly and sets more tubers. Over-aged seed produces a weak plant with few stems.
Production systems
- Furrow-irrigated Delta production: traditional, lower cost, and more exposed to soil-borne disease and to uneven moisture.
- Centre pivot on reclaimed desert land: uniform, high yielding, with precise water control and the option of fertigation.
- Drip with mulch: the highest control over water and nutrition, and the lowest disease pressure, at the highest establishment cost.
Market requirements
Fresh export quality
- Size grading by diameter, commonly 35 to 55 mm, 45 to 65 mm and larger counts depending on market.
- Regular oval or round shape without knobs, dolls or growth cracks.
- Clean, bright, well-set skin. Immature skin that rubs off in handling fails the grade immediately.
- Free of greening, common scab, black scurf, soft rot and visible bruising.
- Free of sprouting at the point of sale.
Processing quality
| Parameter | Target |
|---|---|
| Specific gravity, crisps | 1.080 to 1.095 |
| Specific gravity, french fries | 1.080 and above |
| Reducing sugars, crisps | Very low, since sugar is what turns the crisp dark |
| Internal defects | No hollow heart, no internal brown spot, no black heart |
| Storage temperature | Warmer than for ware, because cold storage converts starch to sugar |
Export and phytosanitary standards
Potato is one of the most heavily regulated crops in international trade. Beyond pesticide Maximum Residue Limits and traceability, importing markets apply quarantine requirements for brown rot, potato cyst nematode and ring rot. For Egypt specifically, access to the European Union runs through a system of designated disease-free zones with official sampling and laboratory screening of soil, water and tubers. A single detection can suspend a zone, which is why brown rot management is a commercial requirement rather than an agronomic preference.
Growth requirements
Temperature
Potato is a cool-season crop. Haulm growth is best between 20 and 25°C, but tuber initiation and bulking need cooler soil, with the optimum between 15 and 20°C. Tuber initiation slows sharply above 25°C soil temperature and effectively stops above 30°C, which is the reason the Egyptian crop is grown in the winter and early spring window rather than through the summer. High night temperature is particularly damaging, because the plant respires away the sugars that should have gone into the tuber.
Growth stages
| Stage | What happens | Duration |
|---|---|---|
| Sprouting and emergence | The plant lives on the seed tuber. Stem number is set here | 2 to 4 weeks from planting |
| Vegetative growth | Canopy, stolons and root system build | 2 to 4 weeks |
| Tuber initiation | Tuber number is fixed, over roughly two weeks, and cannot be increased later | Around 3 to 5 weeks after emergence |
| Tuber bulking | The longest and most demanding phase. Yield accumulates almost linearly with intercepted light | 6 to 10 weeks |
| Maturation and skin set | Haulm senesces, dry matter stabilises, skin hardens for handling | 2 to 3 weeks before harvest |
Day length and light
Short days and high light favour tuber initiation and bulking. Long days with high nitrogen push haulm growth at the expense of tubers, which is the classic cause of a magnificent green crop that yields poorly.
Soil and irrigation
Soil requirements
- Deep, loose, well-drained sandy loam is ideal. The tuber has to expand physically, so soil structure is a yield factor in a way it is not for most crops.
- Optimum soil pH is 5.5 to 6.5. Potato tolerates a wider range, but common scab becomes markedly worse above about pH 6.5, which is a real constraint on the calcareous soils of reclaimed land.
- Avoid compacted layers and plough pans, which cause misshapen tubers and poor drainage.
- Do not plant potato after potato, tomato, pepper or aubergine, since they share soil-borne pathogens and nematodes.
Ridging
Ridges give the tubers room to expand, improve drainage and keep developing tubers covered. Covering matters commercially: an exposed tuber turns green, and green tubers are rejected.
Irrigation
- Seasonal water requirement is approximately 500 to 700 mm, depending on climate, variety and length of season.
- The root system is shallow and concentrated in the ridge, so potato has a small buffer and depletes available water quickly.
- The critical period is from tuber initiation through bulking, when water stress directly costs yield and tuber size.
- Avoid alternating drought and heavy irrigation. It causes second growth, knobby tubers, growth cracks and hollow heart.
- Keep soil moisture adequate during tuber initiation specifically, because dry soil in that window strongly favours common scab.
- Stop irrigation in good time before harvest so the skin sets properly, and because lifting wet soil bruises tubers and spreads soft rot.
What drives yield and quality
Genetic factors
- Variety, which sets maturity, dry matter, shape, dormancy and the disease resistance package.
- Seed health and physiological age, which set emergence speed, stem number and therefore tuber number.
Environmental factors
- Soil and night temperature during tuber initiation and bulking.
- Light interception, which is the product of canopy size and canopy duration.
- Steady soil moisture, and soil structure loose enough for tubers to expand.
Management factors
- Plant spacing and seed size, which set stem number and therefore the balance between tuber number and tuber size.
- A nutrition programme weighted to potassium through bulking, with nitrogen that finishes rather than continues.
- Late blight protection maintained preventively, since the disease moves faster than any curative programme.
- Haulm destruction timing, which sets skin finish and stops tuber growth at the target size.
- Careful lifting and handling, because bruising is invisible on the day and obvious on arrival.
Nutrient demand
Potato is a heavy feeder with a short, intense demand curve and a shallow root system, which means it depends on nutrients being available in the ridge at the right moment rather than merely being present in the soil.
A crop of 40 to 60 t/ha removes approximately:
| Nutrient | Removal |
|---|---|
| Nitrogen (N) | 150 to 220 kg/ha |
| Phosphorus (P₂O₅) | 50 to 90 kg/ha |
| Potassium (K₂O) | 250 to 350 kg/ha |
| Calcium (CaO) | 40 to 80 kg/ha |
| Magnesium (MgO) | 30 to 50 kg/ha |
| Sulfur (S) | 20 to 40 kg/ha |
The defining feature of potato nutrition is the potassium figure. The crop takes up substantially more potassium than nitrogen, commonly around 50% more, and it shows luxury uptake, meaning it will absorb more than it strictly needs when supply is generous. Uptake is modest until tuber initiation, then rises steeply through bulking, when the great majority of the season’s nutrients are taken up in a few weeks.
Because the demand curve is so concentrated, split applications through fertigation consistently outperform a single pre-plant dose, particularly for nitrogen and potassium on sandy soils where both leach.
Macronutrients
Nitrogen (N)
Nitrogen builds the canopy that intercepts the light that fills the tubers. The useful principle is that nitrogen should build the canopy early and then get out of the way.
Deficiency: pale, small canopy, early senescence, and a short bulking period that caps yield.
Excess: the most expensive mistake in potato. Late nitrogen delays tuber initiation, extends haulm growth at the expense of bulking, delays maturity and skin set, lowers dry matter and specific gravity, and raises reducing sugars so processing crops darken on frying. It also makes the crop more attractive to aphids.
Management: apply a starter portion at planting, build through emergence and early vegetative growth, and taper clearly once bulking is established.
Phosphorus (P)
Phosphorus drives root and stolon development and early establishment, and it influences tuber number set at initiation. Demand is highest early, which is why placement at planting matters more than total rate.
Deficiency: stunted plants, dark dull green leaves, poor root development, delayed maturity and fewer tubers.
On calcareous soils availability rather than quantity is the constraint. Band phosphorus near the seed rather than broadcasting it, and use acidifying or fertigated sources to keep it in solution.
Potassium (K)
Potassium is the dominant nutrient in potato. It regulates water movement and drives the transport of sugars from the leaf into the tuber, which makes it the direct driver of tuber size and total yield. It also improves resistance to bruising and blackspot, which is a quality trait the pack house can measure.
Deficiency: marginal scorch on older leaves, a bronzed and cupped appearance, early senescence, small tubers and high bruising susceptibility.
Source matters: muriate of potash is cheaper, but the chloride it carries depresses dry matter and specific gravity. For processing crops and for any crop grown on saline water, potassium sulphate is the correct choice. Where muriate is used on ware crops, apply it well before planting so the chloride can leach.
Calcium (Ca)
Calcium strengthens cell walls in the tuber skin and flesh. It is taken up directly by the developing tuber from the soil around it, not redistributed from the leaves, so calcium has to be present in the ridge during bulking.
Deficiency: internal brown spot, weak skin, higher bruising and more storage breakdown, and in severe cases dieback of growing points.
Magnesium (Mg)
Magnesium is the centre of the chlorophyll molecule and sustains photosynthesis through the long bulking phase, which is when demand peaks.
Deficiency: interveinal yellowing on older leaves with the veins staying green, progressing to necrosis and early leaf loss, which shortens bulking. It is common on sandy soils and is made worse by heavy potassium applications through potassium and magnesium antagonism, a real risk in a crop fertilised this heavily with potassium.
Sulfur (S)
Sulfur is needed for protein synthesis throughout the season. It has a second, very practical role in potato: sulfur and acidifying sulfur sources lower pH in the ridge and are a recognised tool for suppressing common scab.
Deficiency: general yellowing starting on the youngest leaves, similar to nitrogen deficiency but at the top of the plant rather than the bottom.
Micronutrients
Potato is more sensitive than most field crops to boron, zinc and manganese supply, and on the calcareous, high-pH soils of reclaimed land all three are commonly limiting.
BBoron
Supports cell wall formation and calcium movement into the tuber. Deficiency causes brown, corky internal tissue and distorted growing points. The margin to toxicity is narrow, so apply only on a test.
ZnZinc
Involved in enzyme systems and hormone regulation. Deficiency gives small, cupped, bronzed leaves and shortened internodes, and reduces tuber number. Common on high-pH and heavily phosphated soils.
MnManganese
Supports photosynthesis and enzyme activation. Deficiency causes interveinal chlorosis on young leaves with fine dark necrotic speckling along the veins, typical of calcareous soils.
FeIron
Required for chlorophyll synthesis. Lime-induced chlorosis shows as pale young leaves with a fine green vein network. Soil iron sulphate is ineffective at high pH, so use chelate or foliar correction.
CuCopper
Involved in enzyme systems and lignin formation. Deficiency is uncommon and mainly seen on peat and very sandy soils, where it causes wilting and weak stems.
MoMolybdenum
Required for nitrogen metabolism. Deficiency is rare and limited to acidic soils, where it resembles nitrogen deficiency with pale, cupped young leaves.
Correction approach
Soil and leaf analysis should guide correction rather than routine blanket application, particularly for boron. Foliar sprays during early bulking give the fastest correction for zinc and manganese, while chelated soil and fertigation applications give a more sustained supply over the bulking period.
Fertilization by growth stage
- Pre-plant and plantingPlace phosphorus near the seed, since early root and stolon development depends on it and broadcast phosphorus is poorly available on calcareous soil. Apply a starter nitrogen portion, magnesium and sulfur, and the bulk of any muriate-based potassium well ahead of planting.
- Emergence and vegetative growthBuild nitrogen progressively to establish the canopy quickly, since canopy duration is what determines how much light the crop intercepts. Keep potassium and magnesium moving in parallel.
- Tuber initiationThe window that fixes tuber number. Moderate nitrogen deliberately here, because excess nitrogen delays initiation and reduces tuber set. Keep soil moisture steady, which also suppresses common scab. Ensure phosphorus, boron and zinc are available.
- Tuber bulkingThe dominant phase for both yield and nutrient uptake. Potassium becomes the leading requirement, with calcium and magnesium alongside it for tuber quality and canopy duration. Nitrogen is tapered so the crop fills tubers rather than growing more haulm.
- Maturation and skin setStop nitrogen. Allow the haulm to senesce so dry matter stabilises and the skin sets hard enough to survive lifting, grading and shipping.
Physiological disorders
Most potato disorders are not pathogens at all. They are the record of an inconsistency in water, temperature or nutrition, written into the tuber where the grader will find it.
Hollow heart
A star-shaped or lens-shaped cavity in the centre of large tubers, caused by a growth check followed by a rapid growth surge. Associated with wide spacing, irregular water and low tuber number.
Greening
Chlorophyll and solanine develop in tubers exposed to light, whether on the ridge shoulder, at lifting or in the store. Green tubers are rejected outright.
Second growth and knobs
Secondary tubers, dumbbells and knobby shapes, caused by heat stress or by drought followed by heavy irrigation during bulking.
Growth cracks
Deep splits from rapid expansion after a check, with the same cause as second growth and the same remedy: steady soil moisture.
Internal brown spot
Scattered brown necrotic flecks in the flesh, linked to calcium shortage in the tuber combined with heat and water stress during bulking.
Black heart
Dark grey to black tissue in the tuber centre, caused by oxygen starvation in waterlogged soil or in a poorly ventilated store.
Blackspot bruising
Grey to black discolouration under the skin that appears a day or two after impact. Worse in low-potassium crops and in cold or dehydrated tubers, which is why handling temperature matters.
Cold-induced sweetening
Starch converts to reducing sugars when tubers are stored too cold, so crisps and fries come out dark. It is a storage management problem, not a field problem.
Fungal diseases
Late blight Phytophthora infestans
- Water-soaked dark lesions on leaves and stems, spreading rapidly
- White fungal growth on the leaf underside in humid conditions
- Reddish-brown granular rot spreading irregularly into the tuber from the skin
- Destroy cull piles and volunteer plants, which carry the pathogen between seasons
- Ridge well so spores washing off the canopy cannot reach the tubers
- Follow regional blight warning systems where available
- Preventive protectant fungicides such as mancozeb, started before the canopy closes
- Systemic and translaminar fungicides (cymoxanil, metalaxyl, fluazinam combinations) under high pressure
- Destroy the haulm early if blight gets into the crop, to protect the tubers
- Plant certified, blight-free seed
- Choose varieties with better foliar and tuber blight resistance where pressure is chronic
- Treat the programme as preventive from the start. Once late blight is visible, the crop is already behind
Early blight Alternaria solani
- Dark concentric target-like spots on older, lower leaves
- Yellowing and premature defoliation, which shortens bulking
- Dark sunken dry lesions on tubers in severe cases
- Crop rotation away from solanaceous crops
- Avoid nutrient stress, since the disease attacks a weakened, prematurely senescing canopy
- Remove and destroy infected debris
- Protectant fungicides (chlorothalonil, mancozeb)
- Systemic fungicides (azoxystrobin, difenoconazole, boscalid) at first symptoms
- Rotate modes of action to avoid resistance
- Maintain balanced nitrogen and potassium through bulking, because early blight is in large part a disease of a stressed crop
- Avoid overhead irrigation late in the day, which extends leaf wetness
Black scurf and stem canker Rhizoctonia solani
- Hard black sclerotia stuck to the tuber skin, which wash off but fail the grade
- Brown sunken cankers on underground stems and stolons
- Uneven emergence and stunted, bunched plants
- Plant into warm soil so emergence is fast, since the fungus attacks slow-emerging sprouts
- Avoid planting too deep
- Rotate out of potato for at least three years
- Seed tuber treatment with a registered fungicide, which is the main control
- In-furrow fungicide application at planting where pressure is high
- Use certified seed free of visible sclerotia
- Harvest promptly after haulm destruction. Leaving tubers in the ground is what lets black scurf develop on the skin
Fusarium dry rot Fusarium spp.
- Sunken, wrinkled areas on the tuber with internal brown to grey rot and cavities
- Develops in store rather than in the field
- Often followed by soft rot bacteria entering the damaged tissue
- Minimise wounding at lifting and grading, because every infection starts at an injury
- Cure tubers after harvest at a warm temperature with good ventilation so wounds heal
- Clean and disinfect stores and boxes between seasons
- Registered post-harvest seed treatment for seed lots
- No treatment for an affected ware crop in store. Grade out and ship early
- Handle tubers at an appropriate temperature, since cold tubers bruise and split much more readily
Bacterial diseases
Brown rot and bacterial wilt Ralstonia solanacearum
The quarantine disease that governs Egyptian potato access to the European Union
- Rapid wilting of the whole plant in warm conditions, often with leaves still green
- Brown, slimy vascular ring when the stem or tuber is cut
- Greyish bacterial ooze from the tuber vascular ring, and soil sticking to the eyes
- Use only certified seed from tested lots
- Never irrigate with surface water from drains or canals that may carry the bacterium
- Avoid moving soil, water or machinery from suspect fields into clean ones
- Rotate long out of host crops, including tomato, pepper, aubergine and solanaceous weeds
- No chemical cure exists. Infected lots are removed from the trade channel
- Report and act under the official zone programme rather than attempting to manage it privately
- Produce for export inside designated disease-free zones with official soil, water and tuber screening
- Treat irrigation water source as the critical control point, because that is the route that most often re-introduces the bacterium
- Clean and disinfect equipment, boxes and stores between lots
Blackleg and soft rot Pectobacterium spp. / Dickeya spp.
- Black, slimy decay of the stem base, with the plant yellowing and wilting from the top
- Soft, wet, foul-smelling rot of tubers in the field or in store
- Gaps in the stand from seed pieces that rotted before emergence
- Avoid waterlogging and avoid lifting in wet soil
- Do not wash tubers unless they can be dried quickly
- Keep stores cool, dry and well ventilated
- No effective chemical control. Management is hygiene and storage condition
- Grade out affected tubers before they infect the rest of the lot
- Plant certified seed, since the bacteria are carried in and on tubers
- Warm seed before cutting or handling to reduce bruising, and let cut surfaces suberise
Common scab Streptomyces scabies
- Rough, corky, raised or pitted lesions on the tuber skin
- No effect on yield or on eating quality, and a total effect on grade
- Worse on alkaline, dry, light soils, which describes much reclaimed land
- Keep soil moisture high through the three to six weeks after tuber initiation, which is the single most effective measure
- Avoid liming before potato, and avoid fresh manure
- Use acidifying fertilizers, including sulfur and ammonium sulphate, to lower pH in the ridge
- No curative treatment once lesions have formed. The tuber surface does not recover
- Choose less susceptible varieties on high-pH fields
- Rotate with non-host crops such as cereals, and avoid beet and carrot in the rotation
Viral diseases
Potato Virus Y (PVY)
Transmitted by aphids in seconds, without the aphid needing to colonise the plant
- Mosaic mottling, leaf crinkling and vein necrosis
- Stunted plants and sharply reduced yield in the following generation
- Necrotic ringspot on tubers with some strains
- Rogue out symptomatic plants in seed crops
- Mineral oil sprays, which interfere with transmission better than insecticides do
- Control volunteers and weed hosts
- No cure. The virus is carried forward in the tubers of infected plants
- Certified seed is the whole strategy, since the loss appears in the generation after infection
- Do not save your own seed from a ware crop
Potato Leafroll Virus (PLRV)
Transmitted persistently by the peach-potato aphid
- Upward rolling of the lower leaves, which become stiff and leathery
- Stunting and pale, upright plants
- Net necrosis in the tuber flesh of susceptible varieties
- Control colonising aphids, which matters here because transmission is persistent
- Rogue infected plants in seed crops
- No cure. Remove and do not replant affected stock
- Plant certified seed with a low virus tolerance
- Destroy haulm early in seed crops to limit late-season infection reaching the tubers
Insect pests
Potato tuber moth Phthorimaea operculella
- Blotch mines in leaves and tunnelling in stems
- Larvae tunnelling just under the tuber skin, with frass at the entry hole
- Heavy losses in store, where the pest continues to multiply
- Ridge high and keep tubers covered, since the moth lays on exposed tubers and in soil cracks
- Pheromone traps for monitoring and mass trapping
- Harvest promptly and do not leave lifted tubers in the field overnight
- Bacillus thuringiensis and selective insecticides (spinosad, chlorantraniliprole) per label
- Store treatment and sealed storage for seed lots
- Destroy crop residues and cull piles immediately after harvest
- Keep the store insect-proof, because most of the damage is done after the crop leaves the field
Aphids Myzus persicae / Aphis gossypii
- Colonies on the underside of leaves, with curling and honeydew
- The economic damage is virus transmission, not feeding
- Monitor with yellow water traps from emergence
- Conserve lacewings, ladybirds and parasitoid wasps
- Mineral oil, which reduces non-persistent virus transmission
- Selective aphicides (flonicamid, pymetrozine) when thresholds are exceeded
- Rotate insecticide classes, since this aphid develops resistance readily
- Avoid excess nitrogen, which produces the soft growth aphids multiply on
- Destroy haulm on time in seed crops to protect the tubers from late infection
Leafminers Liriomyza spp.
- Winding white mines through the leaf blade
- Premature defoliation under heavy attack, which shortens bulking
- Conserve parasitoid wasps, which usually control the pest unless they are sprayed out
- Yellow sticky traps for monitoring
- Remove heavily mined lower leaves
- Selective insecticides (abamectin, cyromazine) only when defoliation is threatening the canopy
- Avoid repeated broad-spectrum sprays, which cause leafminer outbreaks by removing natural enemies
Wireworms and cutworms Agriotes spp. / Agrotis spp.
- Narrow clean holes bored straight into tubers by wireworms, which downgrade the tuber completely
- Young plants cut at the soil line at night by cutworms
- Avoid planting potato directly after grass, pasture or cereal stubble, where wireworm populations build
- Deep tillage before planting to expose larvae
- Control weeds before planting to remove egg-laying sites
- Soil-applied insecticide at planting where populations are known to be high
- Bait formulations for cutworms near the plant base
- Sample soil for wireworm before planting a high-value crop, since there is no rescue treatment once tubers are holed
- Harvest promptly, because damage accumulates the longer tubers sit in the soil
Nematodes
Root-knot nematode Meloidogyne spp.
- Galls and knots on roots, and raised pimples or bumps on the tuber surface
- Brown specks in the flesh just under the affected skin
- Stunted growth and wilting under heat stress despite adequate water
- Soil solarization before planting on sandy soils
- Rotate with non-host crops such as cereals and onions
- Add organic matter to improve soil biological activity
- Nematicides applied at planting per registered label
- Biological nematicides as part of a longer-term soil programme
- Sample soil before planting, since tuber symptoms arrive too late to act on
- Sanitize equipment to avoid moving infested soil between fields
Potato cyst nematode Globodera rostochiensis / Globodera pallida
A regulated quarantine pest in most importing markets
- Patches of stunted, pale, early-senescing plants rather than a whole-field effect
- Small white, yellow or brown cysts visible on roots when plants are lifted carefully
- Yield decline that worsens year on year in short rotations
- Long rotations, since cysts survive in soil for many years
- Resistant varieties where the species present is known
- Strict machinery and soil hygiene between fields
- Registered nematicides reduce damage but do not eradicate the population
- Official soil testing before planting an export crop, which most destination markets require
- Certified seed only, since the cysts travel in adhering soil
Prevention and IPM
Cultural practices
- Certified seed, every season. Almost every serious potato problem is seed-borne.
- Rotation of at least three to four years out of potato and other solanaceous crops.
- Ridge high and keep tubers covered, which prevents greening, tuber blight and tuber moth at once.
- Steady soil moisture through tuber initiation and bulking.
- Balanced fertilization with nitrogen that finishes before bulking ends.
- Destroy haulm on time, then lift promptly rather than leaving tubers in warm soil.
- Remove cull piles and volunteers, which carry blight and tuber moth into the next crop.
Monitoring and biological control
- Weekly field scouting, with yellow water traps for aphids and pheromone traps for tuber moth.
- Follow blight warning systems and spray ahead of the risk period rather than after symptoms.
- Conserve parasitoid wasps and predatory insects, which hold leafminer and aphid populations down.
- Soil sampling for nematodes before planting, not after a yield loss.
Chemical control and storage
- Apply only registered products at recommended rates, and keep full spray records for export audit.
- Rotate modes of action, particularly in blight fungicides and aphicides.
- Respect pre-harvest intervals, checked against the destination market’s residue limits.
- Cure, cool and ventilate the store correctly. A large share of total potato losses happens after the crop is already out of the ground.
Questions growers ask
Why does potato need so much potassium?
Because potassium drives the movement of sugars from the leaves into the tubers, and a potato crop is essentially a sugar transport operation. A 40 to 60 t/ha crop removes 250 to 350 kg/ha of K₂O against 150 to 220 kg/ha of N, roughly 50% more potassium than nitrogen, and the crop shows luxury uptake on top of that. Potassium also reduces blackspot bruising, which is a measurable quality gain in the pack house.
Should I use muriate of potash or potassium sulphate?
For processing crops, potassium sulphate. The chloride in muriate of potash lowers dry matter and specific gravity, which is exactly what a crisping or fry contract is paying for. The same applies where irrigation water is already saline. On ware crops where cost matters more, muriate can be used if it is applied well before planting so the chloride has time to leach out of the ridge.
Why did my crop grow a huge canopy and yield badly?
That is the signature of too much nitrogen applied too late. Excess nitrogen delays tuber initiation, keeps the plant growing haulm instead of filling tubers, delays maturity and skin set, lowers specific gravity and raises reducing sugars. Nitrogen should build the canopy early and then taper clearly once bulking is established.
How do I reduce common scab on calcareous soil?
Keep the soil moist through the three to six weeks after tuber initiation, which is the most effective single measure. Beyond that: avoid liming before potato and avoid fresh manure, use acidifying fertilizers such as sulfur and ammonium sulphate to lower pH in the ridge, choose less susceptible varieties, and rotate with cereals rather than with beet or carrot. Once the lesions have formed there is no treatment, so all of it is preventive.
What causes hollow heart and growth cracks?
Both are growth checks followed by a surge. A period of heat or drought slows the tuber, then heavy irrigation or a sudden cool spell makes it expand faster than the tissue can follow. Steady irrigation through bulking is the main control. Closer spacing, which gives more tubers of smaller individual size, also reduces hollow heart because the disorder mainly affects the largest tubers.
Why is brown rot such a serious issue for Egyptian exports?
Because it is a quarantine disease with no chemical cure, and European market access runs through a system of designated disease-free zones with official sampling of soil, water and tubers. A detection can suspend a whole zone, not just one grower. The practical controls are certified seed, never irrigating with untested surface water from drains or canals, long rotation out of solanaceous hosts, and strict equipment and store hygiene.
When should I destroy the haulm?
When the tubers have reached the target size for the market, allowing two to three weeks before lifting for the skin to set. Lifting before skin set produces skinning and scuffing that fails the grade and opens the tuber to soft rot. In seed crops the haulm is usually destroyed earlier, to stop late-season aphids carrying virus down into the tubers.
Glossary and units
Chitting
Pre-sprouting seed tubers in light before planting, to speed and even up emergence.
Haulm
The above-ground stems and foliage of the potato plant.
Reducing sugars
Glucose and fructose in the tuber. They brown on frying, so processing contracts set a low limit.
Skin set
Hardening of the tuber periderm after haulm destruction, which allows lifting and grading without skinning.
Specific gravity
A practical measure of tuber dry matter, and the main index of processing quality.
Stolon
The underground stem on whose tip the tuber forms.
Suberisation
Wound healing at the tuber surface, which seals cut or damaged tissue against rot.
Units used here
t/ha tonnes per hectare (yield) · kg/ha kilograms per hectare (nutrient rate) · mm millimetres of water · °C degrees Celsius · EC electrical conductivity, an indicator of salinity.
This guide provides general agronomic reference information and does not replace local extension advice or officially registered product labels. Always verify recommendations against your specific variety, soil, climate and regulatory requirements.
Build a potato nutrition programme around your soil and your contract
The Gate Group agronomy team works with growers and distributors across Egypt, the Middle East and Africa to translate soil and tissue analysis into a practical fertilizer plan.
