Cause A phytoplasma transmitted by several species of leafhopper and within potato seed pieces.
Symptoms Plants from an infected seed piece have multiple and highly branched stems. Leaves are rolled up and have yellow margins. Plants are dwarfed in the field. Stolons are elongated and set many small tubers, giving the effect of a chain of beads. Tubers usually are numerous but no larger than a walnut. Buds on tubers break and give rise to new stems or leafy growths. When a leafhopper transmits the virus, the plant produces many tightly spaced branches whose rolled-up leaves have chlorotic margins. Tubers formed after transmission are small, and buds break as above.
- Plant certified seed.
- Avoid planting near alfalfa or ladino clover fields because they are alternate hosts.
- Kill volunteer clover and alfalfa around potato fields.