Why Are My Potato Leaves Curling Inward?

Curled or rolled potato leaves look alarming, but the cause is often perfectly harmless. Potatoes curl their leaves as a defence mechanism against heat and moisture loss — on a hot afternoon in summer, slightly curled leaves on an otherwise healthy plant are the plant protecting itself. However, leaf curl can also be an early symptom of potato leaf roll virus, a serious disease spread by aphids that can devastate yield and carry over into the following season via infected tubers. Knowing which you have is essential.

Physiological leaf roll — the harmless kind

When temperatures rise above around 25°C and soil moisture is limited, potato leaves roll inward along their midrib — from the edges toward the centre — as the plant reduces its surface area to conserve water. This is particularly common on warm summer afternoons and usually reverses by morning as temperatures drop. Physiological roll affects the upper, younger leaves most noticeably and the plant otherwise looks healthy with good colour and strong stems. If the rolling eases overnight and the plant looks normal in the cooler parts of the day, this is simply heat stress and the plant is coping well. Deep, consistent watering at the root zone helps reduce it.

Potato leaf roll virus

Potato leaf roll virus (PLRV) causes a different, more persistent rolling that starts with the lower leaves and progresses upward over the season. Affected leaves roll tightly upward — not downward — and turn slightly pale or yellowish, feeling stiff and papery to the touch. The rolling does not reverse overnight. In severe infections the plant may be noticeably stunted. PLRV is transmitted by peach-potato aphids (Myzus persicae) and cannot be cured once a plant is infected. Infected tubers carry the virus into next season, which is why growing from certified seed each year is so important.

What to do about leaf roll virus

If you suspect leaf roll virus, remove and destroy the infected plants immediately — do not compost them. This limits the chance of aphids feeding on infected foliage and carrying the virus to neighbouring healthy plants. Monitor all remaining plants carefully and control aphid populations with an organic insecticidal soap spray, focusing on the undersides of leaves where aphids colonise. Do not save tubers from infected plants for seed. For next season, buy new certified virus-free seed potatoes and consider growing varieties with good resistance to PLRV.

Other causes of leaf curl

Less commonly, leaf curl can result from spray drift from herbicides used nearby, particularly if potatoes are grown close to a lawn or path that has been treated. Herbicide-related curl often looks twisted or distorted rather than neatly rolled, and frequently affects the youngest growing tips most severely. If you suspect drift, there is nothing to do but wait and see whether the plants recover once the chemical has broken down. In most cases, healthy established plants do recover from mild herbicide exposure.