PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Disease cycle
See Fig. 157 below.
‘Overwintering’
P. syringae bacteria are always present on leaves
of all stone fruits (healthy and diseased).
Bacteria can also overwinter as actively growing
bacteria in cankers, in infected buds on stone
fruit and other deciduous hosts, and in lesions on
other hosts. Systemically in some hosts.
The disease is not soilborne.
Conditions favoring
Cankers are first noticed in early spring when
gum is produced in most cankers.
Woody tissue of actively growing trees is
generally resistant to canker infection, and that
of dormant trees, susceptible.
Autumn, winter and early spring are the danger
periods for infection.
Wounds, eg pruning scars, hail damage, leaf
scars, stomates and other natural openings during
wet windy conditions in autumn just before and
during leaf fall. Frost injury.
Spread
Movement of infected nursery stock.
By water splash, wind-blown leaves, irrigation
water, insects and pruning tools. Bacteria are
spread from cankers, infected buds, leaf spots
and other lesions on the host to healthy parts.
Fig. 157. Disease cycle of bacterial canker of stone fruit
(Pseudomonas syringae pv. syringae) (adapted from Agrios, 1997).
308 Bacterial diseases