Government of New Brunswick

Verticillium Wilt

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The fungi, Verticillium albo-atrum and V. dahliae, overwinter in infected tubers and in the soil in diseased plant debris. Plants become diseased early in the season either due to the planting of infected tubers or because of attack by the organism present in the soil. Verticillium wilt is often confused with other wilts and early maturity diseases (some are non-infectious, eg. drought). It is also referred to as early dying disease. Early death of leaves and stems on plants begins about flowering time and in irregular patches in the field, particularly on well drained sandy soils. Typically only one stem or one side of a stem will show wilting, especially during hot windy days or dry soil conditions. Wilted stems cut at soil level show brown vascular discolourations. Leaves become yellow, then brown, normally first at the bottom of the plant and then proceeding up the stem. As the whole crop matures, wilted plants may not be easily distinguished from naturally senescing plants.

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Tubers are also affected in that growth and quality can be reduced. Vascular tissues can become discoloured and often harbour the organism over winter resulting in more disease problems the next year if tubers are used for seed.

V. albo-atrum is generally more pathogenic than V. dahliae but disease responses will vary depending on climatic conditions, cultivar and pathogen. The fungi are moved around via infected or contaminated seed pieces and can persist and build up in the soil, if potatoes are grown for several years in succession. Other crops and weeds can also harbour these pathogens. Infection of the potato plant takes place via wounds, root hairs and roots. The fungi grow within the xylem (water conducting) vessels of the potato plant. Inoculum (spores) may be airborne or spread from plant to plant by root contact.

Control

A three or four year crop rotation with cereals or grasses is needed as both fungi will survive in the soil in the absence of potatoes. V. dahliae has a longer survival potential than V. albo-atrum in soil and both have been isolated from forage and pea crops, as well as weeds, oilseeds or legumes. Avoid growing cultivars known to be highly susceptible (e.g. Kennebec, Shepody and Superior). No cultivars are immune but much variation exists in degrees of resistance or susceptibility. Russet Burbank is less susceptible to V. albo-atrum than V. dahliae. Plant parasitic nematodes in the soil can increase disease incidence and severity.

Use disease-free potatoes for seed. In the past, burning or removal of potato vines from fields was practiced to reduce levels of the pathogen in the soil. A recommended seed treatment fungicide (see Publication No. 1300A) should be used immediately prior to planting. Soil fumigants (nematicides, fungicides) are effective but expensive.