Making it Tough to Straighten Out: Venturia Leaf and Shoot Blight
of Poplar
An outbreak of this disease, in a new planting, can pose
problems in establishing a central leader (single trunk) in
woodlot operations if new shoot tips are repeatedly killed.
Regenerating sprouts on recently cut trees can become quite
distorted, resulting in crooked stems and poor canopy
architecture.
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Figure 1. |
The blackened shoot tips and leaves of venturia
leaf and shoot blight are the most obvious symptoms of this
serious disease of poplar. Two species have been reported in
Manitoba: Venturia moreletii and Venturia populina. Both can cause significant damage and symptoms from each are
similar, but slight differences between them influence
management. With the onset of the disease, infected tissues turn
black and killed shoots droop and become brittle (See Figure 1).
All succulent leaves and shoots are susceptible to infection.
Mature parts of the current year’s shoots and all parts formed
in previous years escape infection. In other words, old growth
is not affected directly by these pathogens. The fungi do not
discriminate, attacking plants of all ages and sizes,
potentially killing leaves and shoots throughout the crown.
Generally the younger the stand, the greater the impact, as each
individual shoot and leaf contributes a greater amount to growth
of the plant relative to larger, well established trees. |
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The death of the leaf tips results in distortion of the leaves,
but generally the leaf bases and petioles stay alive when V.
populi is the pathogen. V. moreletii can infect
petioles, turning them black. During dormant seasons, damaged
branches appear to be crowded, stunted and in varying states of
decline (the result of the development of adventitious shoots
and multiple leaders after death of terminal shoots). Canker
causing fungi enter through blighted terminals and can
contribute to the decline. |
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V. populi survives winters only on
blighted shoots. V. moreletii survives on fallen
leaves as well. Early season infections of new leaves from
buds close to the infected and dead shoots begin the disease
cycle and in as little as four days leaf symptoms (spots)
may be observed. At least a week later, a new generation of
leaf borne spores is produced, which give the lesions an
olive-brown appearance. Wet periods with temperatures
ranging from 15°C to 25°C, are suitable for infection to occur.
In Manitoba, the initial release of spores likely begins in
late May or early June and subsequent cycles of infection
continue into mid-July. After this point, the fungus
prepares itself for winter survival and new spore releases
cease until spring.
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| With few available management options this disease is a
challenge to manage. Removal and destruction of blighted
shoots is a good approach, but this may be difficult when
the incidence of disease is high within a planting, and may
not always be practical. Removal of leaf debris is a good
approach regardless, but especially if V. populi is
present, as this fungus overwinters on fallen leaves. |
Author:
Philip
Northover,
Plant Pathologist
Crops Knowledge Centre
Manitoba Agriculture, Food and
Rural Initiatives
Phone: 204-745-5694 |
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For further information, contact your
GO representative.
