Perennial canker of peach is a fungal infection of fruiting twigs, scaffold limbs, or trunks (Fig 1 & 2). The disease may also be referred to as Cytospora canker, Leucostoma canker, perennial canker, valsa canker, or peach canker. A common symptom is oozing gum from canker sites, so symptoms may also be referred to as gummosis (Fig 1).
The causal fungi, Leucostoma spp., are weak pathogens that infect stressed or wounded plants. Infections cause cankers, or stem lesions, that enlarge every year, creating annual rings or target-like growths. These cankers expand until limbs become girdled and die. Cankers often ooze gummy sap (gummosis) that eventually hardens (Fig 1).
Figure 1 – Perennial canker of peach limb, advanced symptoms with oozing sap. (Photo Penn State)
Gummosis can also be caused by other plant injuries such as bacterial infection (bacterial canker of peach), boring or sucking insects, and mechanical damage. It is important to properly diagnose the cause of gummosis before considering management options.
The fungi that cause peach canker produce spores during spring. Fungal spores ooze from cankers during cool rainy weather. Consequently, disease is often more severe during rainy years.
Figure 2 – Infection of peach twigs, early symptoms. (Photo West Virginia University)
Prevention of peach canker begins with vigorous plants and proper orchard sanitation.
· Retain plant vigor. Maintain soil moisture, fertilize according to soil tests, and mulch properly.
· Avoid plant wounds such as mower damage, sunscald, winter injury, and insect injury.
· Make clean, sharp pruning cuts that heal quickly. Avoid jagged cuts.
· Prune peach trees during late winter, preferably during late-February or March.
· Prune during dry weather, only. Fungal spores spread during wet conditions.
· Maintain a clean orchard by pruning dead and damaged wood. Remove cuttings from the orchard; bury, burn, or move them at least 100 yards from peach plantings.
· Some peach cultivars are less susceptible to peach canker than others. Use resistant or tolerant trees when possible.
If peach canker becomes a problem in the orchard, a strict sanitation should be implemented. There are no fungicide treatments available for management of peach canker.
· Remove diseased twigs and limbs, making clean cuts at least 6 inches below cankers. Remove diseased cuttings from the orchard.
· Infected trunks may require “surgery.” Using a knife or chisel, remove bark at least one inch around each disease lesion. There is no need to cut into hardwood. Do not paint affected area with wound dressing, paint, or oil.
· Prune during dry weather, only.
· Disinfest pruners and tools between cuts using a commercial sanitizer, 10% bleach, or 10% Lysol® concentrated disinfectant.
· Apply fungicides to open pruning wounds as a preventative. Captan, iprodione (Rovral), and thiophanate-methyl (Topsin M) may be applied after pruning (delayed dormant phase), after petal fall, and after shuck split to prevent new infections.