Why Are My Potato Leaves Curling?

Physiological leaf roll (harmless)

Physiological leaf roll is the most common cause of potato leaf curl in UK gardens and is completely harmless. It occurs when healthy potato plants roll their leaves upward in response to hot, sunny conditions as a mechanism to reduce water loss and the leaf surface area exposed to direct sun. The roll is most pronounced during the hottest part of the afternoon and reverses as temperatures drop in the evening. It is most visible in warm, dry summers on plants growing in exposed, sunny positions.

How to distinguish from virus

• Physiological roll reverses by evening: if the leaves have uncurled by the following morning, the roll is physiological rather than viral.
• The rolled leaves feel soft and pliable, not stiff or leathery.
• The roll affects the exposed upper leaves uniformly rather than starting from the base of the plant.
• The plant is otherwise healthy, with strong growth and no other symptoms.

Potato leaf roll virus

Potato leaf roll virus (PLRV) is transmitted primarily by peach-potato aphid (Myzus persicae) and is one of the most serious viral diseases of UK potatoes. Primary infection in the current season (from an aphid feeding on the plant) causes the younger leaves near the top of the plant to curl upward with a pale or pinkish margin, and the plant may be somewhat stunted. Secondary infection (from infected seed tubers) is more damaging: all leaves roll tightly, the plant is significantly stunted, and in later-season infection the lower leaves may turn yellow or bronze. Rolled leaves feel stiff and leathery rather than soft.

What to do

• Remove and destroy plants showing definite symptoms of PLRV: do not compost them and do not save their tubers as seed for next year, as the virus is tuber-transmitted.
• Control aphids promptly to reduce the spread of PLRV from infected plants to healthy ones: peach-potato aphid can transmit the virus in as little as 1 to 2 minutes of feeding, so aphid control is most effective as a preventive measure rather than a response to established infection.
• Always buy certified seed potatoes (marked 'Certified Seed' on the packaging) from a reputable UK supplier. Certified seed is grown in northern Scotland where aphid pressure and virus rates are lowest, tested, and guaranteed virus-free.

Drought

Drought causes potato leaves to wilt, droop, and roll inward simultaneously across all parts of the plant, with recovery overnight when temperatures drop. In severe drought, the leaves do not recover overnight and the plant begins to yellow and die back. Potatoes have high water requirements and produce their best yields in consistently moist conditions. In the UK, drought-induced stress is most common in July and August when summer heat and reduced rainfall coincide with the period of tuber bulking.

What to do

• Water potatoes consistently, particularly from when the flowers appear (indicating tuber formation has begun) until the foliage starts to die back naturally. A deep watering every 7 to 10 days in dry weather is more beneficial than frequent shallow watering.
• Earth up the haulm (stem) to cover the base of the plant as it grows, which also helps retain moisture around the developing tubers and prevents them from turning green.

Aphids

Peach-potato aphid (Myzus persicae) and potato aphid (Macrosiphum euphorbiae) both colonise potato plants in the UK, feeding on the underside of leaves and at the growing tips. Heavy infestations cause leaf curl and distortion around the feeding colonies, honeydew deposition, and sooty mould growth on the sticky leaves. More critically, peach-potato aphid is the main vector of potato leaf roll virus and potato virus Y, both of which cause leaf distortion and have economic consequences for saved seed.

What to do

• Inspect the underside of potato leaves regularly from May for aphid colonies. Peach-potato aphid is small, pale green to yellowish, and often waxy in appearance; potato aphid is larger and bright green or pinkish.
• Apply insecticidal soap spray to colonies, covering the undersides of affected leaves. For small colonies, strong water jets or hand removal are effective without the need for any spray.
• Encourage natural predators: ladybirds, parasitic wasps, and hoverflies all provide significant aphid control in gardens with diverse planting around the vegetable beds.

Late blight collapse

Potato blight (Phytophthora infestans) does not directly cause leaf roll but causes rapid collapse of potato foliage that can be confused with severe wilt or virus in its early stages. Early blight symptoms are brown patches on the leaf margins and tips, often with a pale yellow halo, and a distinctive water-soaked appearance on the underside of the leaf. In wet conditions, white fluffy sporulation appears on the underside of patches. The foliage then collapses rapidly, turning brown and collapsing within days in conditions favourable to blight spread.

What to do

• Monitor UK blight warnings from June onward and inspect foliage after periods of warm, wet weather. The RHS and UK Blight Alert services issue warnings when conditions favour blight development.
• If blight is confirmed, cut down the entire haulm to soil level and remove it from the site to prevent blight spores washing down into the soil and infecting the tubers. Wait 2 to 3 weeks before lifting the tubers to allow the skins to set.
• Grow blight-resistant varieties such as 'Sarpo Mira', 'Sarpo Axona', 'Orla', or 'Cara' in areas where blight pressure is consistently high.

Frequently asked questions

Why are my potato leaves curling?

Potato leaves curl most often from potato leaf roll virus, drought, or physiological leaf roll. Potato leaf roll virus (PLRV) is transmitted by peach-potato aphid (Myzus persicae) and causes the lower leaves to roll upward tightly, beginning with the older basal leaves and progressing up the plant. The rolled leaves feel stiff and leathery rather than soft, and the plant may be stunted. Physiological leaf roll is a harmless response to hot, sunny conditions in which healthy potato leaves roll slightly during the hottest part of the day and unfurl in the evening. Drought causes wilting and inward rolling of all leaves simultaneously, recovering with watering.

What is potato leaf roll virus?

Potato leaf roll virus (PLRV) is one of the most damaging viruses of potatoes in the UK, transmitted primarily by peach-potato aphid (Myzus persicae). Primary infection (in the current season from an infected aphid) causes the younger leaves at the top of the plant to roll and the plant to look generally unwell. Secondary infection (in tubers grown from infected seed potato) causes severe rolling of all leaves, purple or yellow discolouration, and significant yield reduction. There is no treatment for PLRV: infected plants should be removed and destroyed. The most important preventive measure is to use certified seed potatoes from a reputable supplier, which are tested and certified free of major viruses.

Is physiological leaf roll harmful to potatoes?

Physiological leaf roll is not harmful to potatoes and does not require any treatment. It is a normal adaptation to hot, sunny weather: the leaves roll to reduce the surface area exposed to direct sun and to reduce water loss through transpiration. The key distinguishing features from virus-caused roll are: physiological leaf roll reverses in the evening or when temperatures drop, the leaves feel soft and pliable (not stiff or leathery), it occurs uniformly across all exposed leaves rather than starting from the base of the plant, and the plant is otherwise healthy with good vigour and no other symptoms.

How do I prevent potato blight in the UK?

Potato blight (Phytophthora infestans) cannot cause leaf roll but is the most damaging disease of UK potatoes and can cause leaf collapse that might be confused with severe drought or virus. Prevention measures include: growing blight-resistant varieties such as 'Sarpo Mira', 'Sarpo Axona', 'Orla', or 'Cara'; planting certified seed potatoes; earthing up to prevent blight spores washing from the foliage onto the tubers; and monitoring for blight warnings via the Blight Alert service (which issues warnings when conditions favour blight development in the UK). There are no approved fungicides for domestic garden use against potato blight in the UK.