Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Potato (Solanum tuberosum) -- Potato Leafroll Virus (Leaf Roll)
 
Cause: The Potato leafroll virus (PLRV) is transmitted by at least 10 species of aphids, in a persistent manner. Once an aphid acquires the virus, it can transmit it for life, but not pass it on to its offspring. The green peach aphid is the most important vector in our area. Infection may come from plants grown from infected tubers or from current season infection by aphids bringing the virus in from other sources. Potential damage is greatest from planting infected seed tubers. Epidemics may be generated from as few as one infection center (e.g. one infected tuber) per acre when aphids are not controlled. The amount of virus allowed in certified potatoes differs among states.

In Idaho seed growing areas, bedding plants purchased for home gardens have been found to harbor both the virus and aphid vectors.

Yield reduction (reduced numbers and size of tubers) is greatest for plants derived from infected tubers, followed by plants initially virus free but infected early in the season from viruliferous aphids. Mature plants show resistance. Important losses also occur from tuber net necrosis, which occurs only from current season infection, not seed borne infection. Affected tubers are not suitable for fresh market, processing, or seed.

Symptoms: Plants from infected tubers show symptoms first on lower leaves. Leaves curl up around the midrib and may assume a leathery texture. Plants usually are yellowed and stunted; reddish-purple coloration of the upper foliage can develop, and older (lower) leaves may brown and die early. Symptoms are more obscure on plants that become infected during the current season. Leaf rolling occurs first on upper (younger) leaves; leaves may be pale green or chlorotic, with purple or reddish borders. Early season infection may result in symptoms typical of tuber-borne leaf roll.

Infected tubers of 'Russet Burbank' may show "net necrosis": small brown speckles or strands of discolored tissue that start at the tuber's stem end and which may extend as far as half way through the tuber. 'White Rose', 'Norgold', and other cultivars do not develop as severe a net necrosis. Net necrosis can occur in the absence of foliar symptoms when plants are infected after leaves have stopped growing but tuber expansion continues. Incidence of net necrosis increases during prolonged storage, especially in medium and small tubers.

Note the plant at the top of the picture with bronzed, rolled leaves.

 
Cultural control:
  1. Use certified seed potatoes with the lowest virus level.
  2. Rogue and destroy infected plants including tubers in seed fields. Because plants may be infected but not showing symptoms, rogue out the three plants on all sides of the infected plant as well.
  3. Control winter annual weeds such as mustard and shepherd's purse, which can harbor the virus, in field borders.
  4. Control volunteer potato plants and eliminate cull piles to reduce inoculum sources.
  5. Do not store potatoes subject to net necrosis for long periods (more than 40 days).
  6. For organic production and home gardens, resistant cultivars can reduce field spread but not eliminate the need for aphid control. Moderately-resistant cultivars include, Katahdin, Kennebec, Norland, Ranger Russet, Red Pontiac, Sangre, Shepody, and Yukon Gold. Resistant cultivars include Abnaki, Atlantic, Cascade, Chieftain, Chippewa, Penobscot, and Sebago. Susceptible cultivars should be avoided, including Green Mountain, Russet Burbank, and Russet Norkotah.
Chemical control: Monitor fields for aphid activity and control aphids. Early and mid-season vector control is most crucial to prevent spread of the virus. Mid- to late-season control is important when growing cultivars susceptible to net necrosis. See PNW Insect Control Handbook for details.
Content edited by: Melodie Putnam and Cynthia M. Ocamb on January 1, 2010
 
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