Biology
Microscopic view of Acospores, the primary
source of scab infection
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Apple
Scab
Apple
scab is a fungal disease and it is one of the most serious
threats to commercial apple production in western Washington.
If uncontrolled, it may defoliate trees and blemish fruit
to a point where it is unmarketable. The fungus survives
the winter in dead leaves on the orchard floor. The overwintering
structure (perithecium) discharges spores (ascospores)
during rainy or wet periods usually from late March thru
mid to late June. These spores landing on wet leaves or
fruit are responsible for initial or primary scab infection.
It is critical to stop this primary infection in order
to control scab in the orchard. Germination of spores and
resulting infection is influenced by temperature and duration
of leaf wetness.
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Powdery mildew infection on Jonagold
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Powdery
Mildew
Powdery
mildew is a fungal disease, which is of considerably less
importance when compared to scab in western Washington.
It overwinters as fungal strands (mycelium) in vegetative
or fruit buds which were infected the previous season.
As buds break dormancy, the fungus mycelium continues to
grow, colonizing developing shoots and causing a powdery
white appearance which is the primary infection. These
infections produce thousands of spores (conidia) which
allow the fungus to spread causing secondary infections
on fruit and leaves throughout the summer. Infections of
fruitlets shortly after bloom can cause web-like russetting
on the mature fruit. Although high relative humidity is
required for infection, spores will not germinate if immersed
in water. The leaf wetting associated with rainfall experienced
in this area is not conducive to mildew development, somewhat
lessening its importance in western Washington.
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The Adult Lygus bug varies from pale green
to dark brown, and has yellow and brown markings.
The Consperse Stink Bug is pale brown with
small red spots
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Sucking
Insects
Both
lygus bugs and stink bugs can feed on and damage fruit.
Lygus
bugs overwinter as adults beneath weeds or duff on the
orchard floor or in adjacent uncultivated areas. They are
about ¼ inch long, green to dark brown in color with a
yellow triangular region (scutellum) on the upper center
of the back. They become active in the spring, fly to fruit
trees, and feed on developing flower buds or young fruit.
They have 3-4 generations per season. Apples are most susceptible
to damage between early pink stage (bud stage 5-6) through
2 weeks after petal fall. Feeding kills some cells in the
fruit, which fail to grow, leaving the fruit deformed and
with deep pits when mature.
Stink
bugs are larger than lygus bugs, green or brown in color
and shaped like a shield. The most common are the consperse
stink bug (brown) and the green soldier bug (green). They
are ½ to ¾ inches long, move quickly when disturbed and
are capable of flying. They overwinter as adults within
the orchard or in nearby brush piles or other protected
areas. They become active in April, feeding on broadleaf
weeds in or around the orchard. Some immediately lay eggs
on trees at this time. When this happens, fruit can be
damaged by nymphs which hatch from these eggs. They have
2-3 generations per season. Most damage from stink bugs
occurs on borders later in the season. Adults puncture
fruit with their beaks causing a sunken appearance with
brown discoloration, similar to bitter pit except that
feeding damage is typically around the top of the fruit,
which helps distinguish it from bitter pit (usually near
the bottom).
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In the spring, Leafroller larvae feed on
expanding leaves and flower clusters.
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Leafrollers
There
are several different species of tortricid moths called
leafrollers, which can be damaging on apples. The most
common leafroller found in Whatcom county is the obliquebanded
leafroller. It overwinters as a 2nd or 3rd instar caterpillar
(larva) within a silken case (hibernaculum) which may be
found in crevices on the tree bark. Young caterpillars
become active in the early spring at about half inch green
stage when they migrate within the tree to feed initially
on opening buds and then on expanding leaves and flower
clusters. The name leafroller comes from the caterpillar's
habit of rolling or tying leaves together when building
sheltered feeding sites. These overwintering caterpillars
complete their feeding in mid to late May, when they pupate
and then emerge as adult moths during June. OBLR worms
have a green body with a dark brown to black head capsule
and thoracic shield, and are about 1 inch long when mature. |
