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).
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Figure 1 – Perennial canker of peach limb, advanced symptoms
with oozing sap. (Photo Penn State)
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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.
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Figure 2 – Infection of peach twigs, early symptoms. (Photo West Virginia University)
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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.
