Grape (Vitis spp.)-Black Foot Disease

See:

Cause This root disease has been found more frequently during the 2010s in the Pacific Northwest. Many different soilborne fungi have been reported to cause this disease including 24 species in these genera; Dactylonectria, Ilyonectria, Neonectria and Thelonectria (Cylindrocarpon-like fungi); Campylocarpon and Cylindrocladriella. In the PNW, Ilyonectria destructans (formerly C. destructans) and Neonectria obtusispora (formerly C. obtusisporum) have been found in association with declining young vines, but the disease has not been thoroughly investigated. Surveys in British Columbia found 5 fungal species associated with this disease; Ilyonectria liriodendri and I. macrodidyma were the most prevalent.

Vines are predisposed to the pathogenic phase of these fungi by stress, in particular water stress. Blocked xylem vessels accentuate the water stress and lead to insufficient water and nutrient supply resulting in symptom expression, which usually occurs during periods of high water demand. Environmental factors and host stress such as malnutrition, poor drainage, soil compaction, heavy crop loads on young plants, planting of vines in poorly prepared soil, improper planting holes, "J"-rooted vines, root girdling, graft failure, crown gall, and gopher damage can all contribute to development of disease.

Vines derived from infected mother plants are thought to be a significant means by which disease is introduced into a vineyard. However, vineyard soils that have been in grapes previously may already contain the pathogens. Cylindrocarpon-like fungi invade through wounds or natural openings in roots and below-ground stem pieces. Poor conditions during cold storage and transport of nursery stock can result in stress; cross-contamination from infected to healthy material can occur at these times.

Symptoms Young vines generally appear normal at planting, but differences in vigor become marked including reduced caliper size of the trunk, shortened internodes, reduced foliage, and reduced leaf size. The first 3 to 5 years after planting, onset of foliar symptoms may appear as severe leaf scorching, followed by necrosis and early defoliation. Wilting and dieback may also occur. Below ground, symptoms include reduced total root biomass, reduced numbers of feeder roots, and sunken, necrotic root lesions. Uneven wood maturity, usually associated with rapid desiccation, is another common symptom.

Viewing trunks of declining grapevines in cross-section, dark brown to black streaking is evident in the vascular elements due to plugging of individual or aggregates of xylem vessels with amber to black gum (gummosis) and formation of tyloses. Necrosis extending from the bark to the pith is characteristic of black foot disease.

Physical injuries to the grapevine due to root tearing, disbudding, or other trauma during production or planting can result in phenolic depositions and black discoloration, or even outright death of tissue as the result of injury to cambium tissues.

Symptoms of young vine decline resemble other important diseases of grape including uneven wood maturity as in Pierce's disease, virus-induced incompatibility, esca or black measles, and some nutrient deficiencies.

Cultural control Management starts with preventive practices in nursery mother blocks and propagation beds. Good management techniques, which include proper planting, irrigation, and fertility for young vines while avoiding devigorating stresses, both before and after planting, are very important for establishing a healthy and productive vineyard.

In the nursery:

  • Strict sanitation and protection of all wounds from pruning to grafting will help protect vines during nursery production. Frequently disinfest pruning shears, hydration tanks, grafting machines, and callusing rooms.
  • Trellis mother vines, even for rootstock production, to lower soil borne pathogen contamination.
  • Grow mother vines in well-drained soil or raised beds. Use drip irrigation that does not overwet the root crown.
  • Immediately after grafting, nurseries should dip vines into specialized waxes containing plant growth regulators or fungicide-impregnated formulations, which encourage graft union callus development while inhibiting fungal contamination.
  • Soak dormant cuttings 30 min. in hot water (122°F or 50°C). This has not always been effective and must be combined with other methods.

In the vineyard:

  • When planting, sort out vines of poor quality. Do not plant vines that have been rooted from a curved cane (J-rooted), have weak or spindly growth or obvious problems such as crown gall. If you must use these kinds of vines, then cluster them in rows where they can be monitored in future years.
  • Delay fruiting for several years until vines have balanced root and shoot growth. Cropping several tons in the second year after planting has been associated with these diseases.
  • Using grow tubes also has been associated with these diseases. It is suspected that grow tubes favor shoot growth over root growth.
  • Plant new vineyards in spring or fall when water is not a limiting factor. Irrigate new plantings for a few years before switching to dryland production.

Chemical control Chemical strategies to control these pathogens are difficult, as traditional techniques used for the control of surface pathogens do not penetrate dormant grapevine cuttings sufficiently to control fungi inhabiting the vascular system. Soaking infected dormant cuttings or vines in fungicides before grafting or planting has reduced disease incidence and severity but none are registered for this use.

Biological control Use in conjunction with other control tactics such as thorough sanitation. Trichoderma sp. have been shown to help protect pruning wounds, basal ends of propagation material and graft unions before infection.

  • RootShield Granules (Trichoderma harzianum Rifai strain T-22) at various rates depending on the specific use. For example, use 1 to 1.5 lb/ cubic yard soil mix or 1,000 sq ft before nursery planting. Zero reentry interval. O
  • Bio-Tam 2.0 or Tenet WP (Trichoderma asperellum and T. gamsii) at 0.5 to 1.5 lb/cubic yard of substrate. See label for details and other application methods. May take a few weeks after application to be effective. No restrictions on reentry when soil incorporated. O

Reference Gramaje, D., Úrbez-Torres, J.R., and Sosnowski, M.R. 2018. Managing grapevine trunk diseases with respect to etiology and epidemiology: current strategies and future prospects. Plant Disease 102:12-39.