What the canopy cannot tell us: Heat damage hidden inside the potato ridge

Recent potato losses in East Asia reveal a production risk that irrigation alone cannot solve: the temperature building around the developing tubers

By Lukie Pieterse, Editor/Publisher of Potato News Today

When South Korean grower Lee Sang-hyuk entered a potato field in Gangwon province during the August heatwave, the crop above ground had given little warning of what he would find beneath it. A week earlier, the field had appeared normal. When the potatoes were lifted, however, the tubers were soft and commercially unusable. Lee compared their condition to potatoes that had been boiled.

The description travelled quickly because it was dramatic. The more important point is agronomic: a potato canopy that still looks serviceable can conceal serious damage inside the ridge.

South Korea’s heatwave formed part of a wider period of exceptional temperatures across East Asia. The country recorded 42.5°C at Yangsan on 2 August 2026—the highest temperature reported there since modern observations began in 1904. Extreme heat also affected Japan, China, Hong Kong and North Korea.

According to reporting published by The Guardian, the damage in Gangwon was not confined to one potato field. The event exposed something the global potato industry must now confront more directly: heat stress is not simply a question of wilted leaves and irrigation demand. It can interrupt tuber formation, distort quality and damage the harvested product while much of the problem remains hidden from view.

The ridge has its own climate

Growers commonly rely on weather stations and air-temperature forecasts to judge heat risk. Those measurements are useful, but the developing tuber does not experience the temperature recorded two metres above the ground.

It lives in a shallow soil environment shaped by solar radiation, soil moisture, ridge dimensions, soil colour, canopy cover, irrigation and wind. Under exposed conditions, the temperature inside the upper ridge can differ markedly from the standard air reading.

This distinction matters because potatoes evolved as a cool-season crop. The plant may continue producing leaves and stems under temperatures that are already disrupting the signals responsible for tuber initiation and bulking.

High daytime temperatures increase respiration and water demand. Warm nights are particularly damaging because the plant continues consuming carbohydrates through respiration when it should be transferring and storing them in developing tubers.

The visible canopy may therefore continue growing while less of the plant’s energy reaches the part of the crop that will be sold.

Heat can also shorten the crop cycle. A plant that develops more quickly is not necessarily producing more. It may simply reach maturity sooner, leaving fewer effective days for tuber bulking and dry-matter accumulation.

Three degrees changed the crop

Evidence from China provides a useful warning about what apparently modest warming can mean.

International Potato Center researcher Li Jieping led controlled experiments using two widely cultivated Chinese potato varieties. Plants were grown under conditions intended to simulate temperatures approximately 3°C above the present average in northern potato-producing regions such as Hebei and Inner Mongolia.

The warmer conditions accelerated development by about ten days—but reduced yield by more than half. The harvested tubers were considerably smaller than those produced under the current-temperature treatment.

The experiment was not a forecast that every potato field will lose half its yield when temperatures rise by 3°C. Controlled environments cannot reproduce all the interactions found in commercial fields, and varieties differ substantially in heat response.

The result nevertheless demonstrates why a longer frost-free season should not automatically be interpreted as a longer productive season. Development can speed up while commercially useful growth declines.

When Reuters reported on the research, Li warned that lower tuber production would affect both food security and growers’ livelihoods. That concern is especially important in China, the world’s largest potato-producing country, but the underlying biology applies far beyond it.

Heat and drought are related—but not identical

A hot potato crop is frequently also a water-stressed crop. The two pressures interact, but they are not the same problem.

When soil moisture declines, plants close their stomata to conserve water. Photosynthesis falls, canopy growth slows and less energy is available for tuber development. Irrigation can relieve that form of stress when sufficient water and delivery capacity are available.

Irrigation may also cool the soil temporarily through evaporation. A moist ridge generally responds differently to solar heating than a dry one.

But water does not cancel temperature.

A fully irrigated crop can still experience reduced tuber initiation, elevated respiration and quality problems during sustained high temperatures—particularly when nights remain warm. Applying more water than the root zone can hold may instead cause nutrient loss, poor aeration, erosion or disease-favourable conditions.

The practical objective is not to use irrigation as a general antidote to heat. It is to maintain consistent soil moisture while avoiding the sharp wetting-and-drying cycles that compound heat injury.

This distinction is commercially important. In water-limited regions, advice to irrigate more may be physically impossible. Even where water is available, pumping capacity is generally designed around historical peak demand. A heatwave affecting an entire district can expose the limits of wells, reservoirs, allocations and electricity infrastructure at the same time.

Quality may fail before tonnage does

Yield is only one part of the heat equation.

Temperature and uneven moisture can contribute to second growth, misshapen tubers, growth cracks and internal physiological disorders. High soil temperatures near the ridge surface may increase the risk of damage to shallow tubers, while interrupted growth can produce a size profile that fails the intended market.

Processing crops face additional concerns. Heat stress can alter dry-matter accumulation and sugar metabolism, affecting fry colour, texture and processing recovery. A field may retain respectable gross tonnage while losing a disproportionate share of its contract value.

This is why post-heat assessment should include more than a yield estimate.

Regular digs can track tuber number, size distribution, shape, internal condition and specific gravity. Samples should represent different soil zones and irrigation positions rather than only the most accessible part of the field.

After severe heat, storage managers also need an accurate field history. Tubers exposed to physiological stress may not behave like an unstressed crop, even when the defects are not immediately obvious at intake. Field identity should be maintained long enough to evaluate storability rather than allowing uncertain lots to disappear into a large bulk store.

The canopy is also cooling infrastructure

A complete potato canopy shades the ridge and reduces direct solar heating. Its value is therefore not limited to intercepting light for photosynthesis.

Anything that delays canopy closure can leave the soil exposed during the period when tubers are beginning to form. Poor seed vigour, compaction, nutrient imbalance, early disease, herbicide injury and irregular emergence may all increase heat exposure indirectly.

That creates a useful management principle: protecting early canopy development is part of heat management.

Ridge design matters as well. Planting depth and the amount of soil covering developing tubers influence the temperature they experience, but deeper is not automatically better. Excessive depth may delay emergence, worsen harvesting losses or place seed into colder, wetter or more compacted soil.

Mulches and retained surface residues can moderate soil temperature in some systems. They may also alter moisture, pest populations, disease risk and harvesting practicality. Their value should be tested locally rather than promoted as a universal solution for mechanised potato production.

The same applies to planting date. Moving the crop so that tuber initiation and early bulking avoid the hottest historical period may reduce exposure. But altered timing can introduce frost risk, conflict with rotation and labour schedules, or move harvest into wetter conditions.

Adaptation always exchanges one risk for another. The task is to make that exchange deliberately.

Not every farm has the same room to adapt

The advice most easily offered after a heat event—change variety, improve irrigation, move the planting window or install better monitoring—assumes that the grower controls those decisions.

Many do not.

Contract specifications may restrict cultivar choice. Seed availability determines what can actually be planted. Water rights and pumping capacity limit irrigation. Tenancy arrangements may discourage long-term investment, while processors and retailers influence planting and delivery periods.

Smallholders face an even narrower range of choices. A grower without irrigation cannot cool a ridge with water that does not exist. A farmer dependent on saved or locally traded seed cannot immediately obtain a newly released heat-tolerant cultivar. Moving production to higher ground may mean leaving established markets, communities and land rights behind.

The human consequence of heat is therefore distributed unevenly. Better-resourced businesses can purchase monitoring equipment, diversify fields and absorb an experimental season. Others carry most of the risk personally when a crop that looked sound above ground fails below it.

Climate adaptation will be incomplete if it consists only of technical recommendations to growers. Contracts, insurance, water policy, seed multiplication and extension services must adapt as well.

Breeding must protect quality, not just survival

Heat-tolerant breeding is advancing in China, at the International Potato Center and within national and commercial programmes elsewhere.

The objective is not simply to produce a plant that remains green at high temperature. A useful variety must still initiate and bulk tubers, produce acceptable dry matter and shape, resist locally important diseases, store reliably and meet the requirements of consumers or processors.

Those traits do not always travel together.

A clone may maintain yield under heat but mature too late for the production system. It may tolerate warm soils but produce unacceptable fry colour. It may perform well in a controlled chamber and respond differently when heat arrives together with drought, intense radiation, a warm night and disease pressure.

Breeding programmes therefore need field trials across contrasting environments and seasons. They also need growers and buyers involved early enough to define what “tolerance” must deliver commercially.

A cultivar that survives heat but cannot enter the market is a scientific result—not yet an adaptation.

Measuring what the tuber experiences

The Gangwon losses underline the limits of canopy observation alone.

An inexpensive soil-temperature probe placed at tuber depth can provide information that a regional weather station cannot. Sensors should represent the actual production zones: the exposed side of a ridge, areas with weaker canopy, different soil types and contrasting irrigation positions.

The value lies less in collecting a perfect stream of data than in connecting temperature to crop response.

Growers can record when critical thresholds persist, then compare those periods with digs, grade, specific gravity, defects and storage performance. Over several seasons, the business begins building its own evidence about which fields, cultivars and growth stages are most vulnerable.

Remote sensing can identify canopy stress and surface-temperature patterns across large areas. It cannot inspect the condition of the developing tubers. Field digging remains indispensable.

The strongest system combines forecasts, soil measurements, canopy observations, irrigation records and physical sampling. Each sees a different part of the problem.

The warning from beneath the ground

It would be misleading to describe every soft or damaged tuber found during a heatwave as literally “boiled” in the soil. The phrase captures a grower’s experience, not a formal diagnosis. Disease, waterlogging and other disorders may also contribute to deterioration and should be investigated.

But the field account from South Korea should not be dismissed because the language was dramatic.

It revealed the particular danger of a crop whose harvest develops out of sight. By the time the canopy communicates the full severity of heat stress, part of the commercial loss may already be fixed.

Potato production has traditionally managed temperature through geography and timing: growing in cooler seasons, temperate regions or higher elevations. Those advantages are becoming less dependable as extreme heat reaches areas once considered naturally protected.

The response will require better varieties, more precise irrigation, protected soil, adaptable planting windows and storage decisions informed by what happened in the field. It will also require contracts and public policy that do not leave growers carrying climate risk alone.

The next damaging heatwave will not wait for all those systems to be ready.

For now, the most practical change may be the simplest one: stop treating the air temperature as the whole story. The potato is forming below the canopy, inside a ridge with a climate of its own.

That is where the industry must learn to look.