Overview
Xanthomonas arboricola is a Gram-negative bacterium whose pathovars cause several of the most economically important bacterial diseases of nut and stone-fruit crops. Pv. juglandis causes walnut blight, one of the principal diseases limiting walnut production worldwide; pv. corylina causes bacterial blight of hazelnut; and pv. pruni causes bacterial spot of peach, plum, apricot and almond.
Symptoms
On walnut, the bacterium infects developing nuts, catkins, shoots and leaves, producing black, greasy lesions; early-season infection of young fruit causes drop and direct yield loss. On stone fruit, pv. pruni causes angular leaf spots, fruit lesions and twig cankers.
How it spreads
Warm, wet and humid conditions during flowering and early fruit development drive epidemics. The bacterium overwinters in buds and cankers, and is spread by rain splash, pollen and contaminated equipment.
The control challenge
As with Pseudomonas, control depends heavily on copper sprays — and copper-tolerant Xanthomonas strains are increasingly common, weakening the main tool available to growers. Effective, residue-free alternatives are needed, particularly for high-value export crops where residue limits matter.
Xanthomonas arboricola is a primary research focus of Exacta's bacteriophage platform. Host-specific bacteriophages offer a targeted route to this pathogen group that avoids the residues and resistance pressure of copper. This describes a research and development area, not a commercially available product.