Why Are My Sweet Potato Leaves Mottled and Distorted?

Leaves that show an irregular yellow-green mosaic pattern — lighter and darker patches scattered across the leaf surface — combined with distortion, puckering, or a feathery, finely divided appearance at the leaf edges are showing the classic symptoms of sweet potato virus disease. Several viruses affect sweet potato; the most economically significant are Sweet Potato Feathery Mottle Virus (SPFMV) and Sweet Potato Chlorotic Stunt Virus (SPCSV). When both infect the same plant simultaneously, the combined damage (called sweet potato virus disease, SPVD) causes severe stunting and yield loss of up to 80%.

Identifying virus infection

Look for a combination of symptoms: irregular yellow-green mosaic or mottling on the leaves, distorted or feathery leaf edges (particularly with SPFMV), strong yellowing with distortion in severe SPVD infections, and overall stunting of the plant compared to its neighbours. The symptoms are most visible in young growing-tip leaves, which show the most pronounced distortion. Unlike nutrient deficiencies, virus symptoms do not appear uniformly on all leaves and do not improve with watering or feeding.

How viruses spread

Sweet potato viruses are primarily spread by aphids in a non-persistent manner — meaning the aphid acquires the virus very quickly while feeding on an infected plant and transmits it almost immediately when it moves to a healthy plant. This happens faster than any contact insecticide can work. Even killing aphids with insecticides does not effectively prevent virus transmission because the aphid transmits the virus during the initial probe before it has taken a substantial feed. The only effective aphid-based control is to prevent aphids landing on plants using physical exclusion (fine mesh netting) or reflective mulches that disorient flying aphids.

Managing infected plants

There is no chemical cure for virus-infected sweet potato. Once a plant shows clear virus symptoms, remove and destroy it immediately. Do not compost it — dispose in household waste. Removing infected plants promptly reduces the virus source for aphids moving to healthy plants. Harvest tubers from infected plants if they are a usable size, but do not use those tubers for propagating slips — virus is carried internally in the tuber and slips taken from it will be infected from the start.

Prevention

The single most effective prevention is to source certified virus-tested, virus-free slips from a reputable supplier each year. Do not propagate from supermarket sweet potatoes or from previous years' plants unless you are certain they were virus-free throughout the season. Manage aphid populations early and proactively. Remove any bindweed (morning glory family) from the garden — several bindweed species are alternative hosts for sweet potato viruses.