Potato (Solanum tuberosum)-Purple Top

Latest revision: 
March 2023

By P. B. Hamm and C. M. Ocamb

Cause A phytoplasma, also called BLTVA for Beet Leafhopper-transmitted Virescence Agent (a member of phytoplasma group 16SrVI in the PNW region). This disease caused substantial damage in 2002 in the Columbia Basin and additional damage during 2003. The main disease sources are infected potato seed, ladino clover, and perennial weeds. Aster yellows, which is not commonly found, cannot be separated from BLTVA without laboratory testing.

Symptoms Tip leaves begin to roll up, and plants develop an off-green or yellowish cast. Aerial tubers form and leaves have a purplish cast. Interveinal leaf tissue may die, giving stems and leaf ribs a more prominent appearance. Plants may wilt quickly and fall over. Tubers are smaller, soft, and flabby. Some plants have numerous small tubers; others develop one or two giant, rough tubers. Psyllid yellows or zebra chip may cause similar symptoms.

Cultural control

  • Plant only certified seed potatoes.

Chemical control

  • Careful monitoring of the vector and timely applications of insecticides are very important. In the Columbia Basin area, leafhoppers migrate to potatoes as surrounding desert vegetation dries up. Use of products in mid-May to early June, when leafhoppers populations are increasing due to a natural buildup, will substantially reduce the amount of disease.
  • For materials, rates, and procedures, consult the PNW Insect Management Handbook.