PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Bacterial canker of stone fruit
Gummosis, Blast
This is a serious disease of ornamental and
fruiting stone fruits. Infection of young trees is
particularly severe often killing them.
Scientific name
A bacterium (Pseudomonas syringae pv. syringae).
P. syringae pv. morsprunorum may also occur on
cherry and plum in some areas.
Host range
Wide range of plants including:
Fruit & ornamentals, eg all fruiting and
ornamental stone fruit, especially apricot, sweet
cherry; also citrus, rose, lilac, poplar.
Vegetables, eg beans and peas.
A particular strain of bacteria may be restricted to
a particular host or group of related hosts, so that
the organism causing citrus blast may not be able
to attack cherry and vice versa.
Symptoms
The disease is most serious on young trees.
Buds. Dormant buds may be blighted, resulting
in the death of the bud and the formation of small
cankers at the base. Flowers. Blossom blight
may develop in favourable weather and this may
develop into twig blight. Leaves. Water soaked
spots develop which rapidly become brown and
drop out giving a ‘shot-hole’ effect. Infection may
result in thin yellow leaves which may be rolled.
In moist conditions, young sappy shoots may wilt
as a result of infection. There may be prolific
defoliation in spring. Fruit of apricot and cherry
trees develop sunken black lesions with underlying
gum pockets. However, lesions on fruit are
variable. Severe fruit infection is most common
in cherry.
Branches and trunks. The most destructive
damage is caused by the development of cankers
on branches and trunks. Cankers extend more
rapidly along a branch than round it, and may be
more than 100 cm long before the branch is girdled
and killed. Stem infection of young trees is usually
fatal. There are 2 types of canker:
Gummosis canker. Water soluble gum
exudes from elongated dead areas of bark. The
underlying wood shows extensive browning.
Soursap canker. First noticed as a slightly
sunken zone but if the bark is cut away dead
tissue is found underneath. Later the bark is
brown, moist or gummy and sour smelling, little
or no gum is exuded. These cankers may not be
noticed until spring when growth begins and
limbs and even whole trees may collapse and
die. Where a branch has been killed by girdling
there is often prolific new growth below the
canker.
Roots are seldom attacked.
General. Infection of young trees is particularly
severe and often results in their death.
Diagnostics. On stone fruit.
State Fact Sheets are available online.
Do not confuse bacterial canker with:
– Bacterial spot of stone fruit (Xanthomonas
arboricola pv. pruni.
– Phytophthora trunk, collar and root rots
(Phytophthora spp.).
– Fireblight (if established in Australia).
Seek expert advice from a diagnostic service.
Various stages of fruit infection
Gumming on stem
Bark removed, brown
dead tissue beneath
Cherry leaves with brown
Dieback of leaders and
bud failure due to leaf
scar infections
Fig. 156. Bacterial canker of stone fruit (Pseudomonas syringae pv. syringae).
Left: PhotoCIT, Canberra (P.W.Unger). Centre and Right: PhotoNSW Dept. of Industry and Investment...
Bacterial diseases 307