Orchardists use weather stations(Metos
shown here) to record temperature and leaf wetness periods;
Critical for predicting scab infection.
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Apple
Scab
Most
growers automatically apply a fungicide at the half inch
green stage as an initial measure to protect emerging
foliage from primary scab infection. After this initial spray,
there are two approaches to controlling primary scab using
fungicides. They are a Protectant program or an Eradicant program.
In the protectant program, sprays are applied every 7-10
days for the entire primary infection period until all of
the overwintering ascospores have been discharged (usually
about mid to late June when apples are ½ inch in diameter).
This approach requires about 10 to 11 sprays, which may be
impractical to some growers who have large acreage and only
one tractor and sprayer. However, in the maritime climate
of western Washington, which is very favorable for scab infection,
many growers are shifting to a protectant program to reduce
the guesswork and minimize the risk of scab infection.
In the eradicant program, spray scheduling is based upon
the determination that environmental conditions within your
orchard are favorable for infection (an infection period
has occurred). There are several methods to help determine
whether an infection period has occurred. Some growers use
computerized scab prediction models (Metos system) which
are driven by instrumentation in place in the orchard. Instruments
record temperature and the time period of leaf wetness. These
values are automatically fed into a computer model which
is capable of identifying if and when infection has occurred
and the relative degree or seriousness of an infection period.
This information can then be used to determine fairly precisely,
given the characteristics of different fungicides, a deadline
for treatment in order to kickback or stop the infection
from progressing within the leaf tissue. The kickback or
reachback period for various eradicant fungicides is specified
on the product label. As an alternative to a computer generated
model, growers can use leaf wetness and temperature guages
in the orchard, and compare their measurements to the Scab
Infection Table shown in the Tables and Charts section page
5-3, to identify scab infection periods. This method is considerably
less expensive than a computerized scab prediction model
but does require close monitoring of instrumentation and
simple mathematical calculations performed in a timely fashion.
Whatcom county growers who use an eradicant strategy usually
make six or seven fungicide applications from half inch green
stage through mid to late June to control primary scab.
The potential threat from this disease in western Washington
is not to be underestimated. Some growers who have used an
eradicant approach in recent years have experienced poor
control. In these situations, fruit and foliar lesions have
first been observed in late May to early June, which is towards
the end of the primary scab infection period. The specific
reasons for these failures are not precisely understood and
are possibly due to one or more of these factors:
- Gala variety is most susceptible.
- Low rate of fungicide application relative to disease
pressure.
- Exceeding the kickback period beyond the capability of
the fungicide.
- Favorable weather conditions for the disease and higher
than ordinary disease inoculum levels.
- Disease may be resistant to certain eradicant fungicides.
- Dilution of fungicide active ingredient on the leaf surface
due to rain.
- For these reasons, when using an eradicant approach,
consider the factors above and err on the conservative
side to minimize the opportunity for error.
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Beating tray used to monitor pest and benificial
insect activity.
Deformed fruit caused by Lygus Bug feeding
when fruit was small.
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Sucking Insects
The beating tray is a useful tool to dislodge and then identify
insects which are active on buds and expanding leaves. Prior
to early pink stage;
- Visit 3 to 5 sites within the orchard and along borders.
- At each site, take at least ten tray samples and record
the total number and identity of insects detected (lygus
bugs, stink bugs, syneta beetle, minute pirate bugs are
most common).
- Hold the tray just below the branch and strike the branch
lightly three times with a short section of rubber sprayer
hose.
- Insects which fall to the tray may fly off quickly. It
is therefore necessary to look at the tray and mentally
record the results as you go from tree to tree until you
have completed ten samples at each site.
- Alternate samples between the rows, at various heights,
and check every other tree until ten branches have been
sampled. Record the results.
- This sampling should be done during the heat of the
day when lygus bugs are more active and in the trees.
There are no established decision-making thresholds based
on this sampling procedure. Even seemingly low density of
lygus or stink bugs may cause excessive damage to fruit.
Many growers routinely apply an insecticide prior to bloom
(pre-bee spray) due to their experience with early season
fruit deformity from sucking insects. Regardless of this,
this sampling procedure is a useful way to:
- Confirm that the target pest is present.
- Compare pre- and post-treatment counts of pests and beneficials.
- Detect other arthropods for later identification and
pest status.
- Familiarize yourself with beneficial and pest insects
in your orchard.
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Young Obliquebanded Leafroller larva
Leafroller larvae feed on expanding leaves
and flower clusters.
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Obliquebanded leafroller
It can be difficult to detect larvae between green tip and
tight cluster stage by visual examination in the field. To
accurately estimate leafroller density during this period,
buds can be collected from the field and returned to the
home or shop for examination under magnification. This sampling
procedure, although time consuming, can be used as a management
tool to determine if a delayed-dormant control is necessary:
- Collect at least 150 fruit buds (6 buds from 25 trees)
from a block (5 acres).
By the tight cluster stage to pink stage, larvae can be
detected without magnification as webbing and feeding damage
is more obvious at this time. The following sampling program
is adapted from a sequential sampling system discussed in
the Cornell Apple IPM program manual. It may be useful for
confirming OBLR presence and justification for treatment
during the pink and bloom stages.
- Examine 10 bud clusters or expanding terminals per tree
for live OBLR larvae.
- Choose half of your clusters or terminals from inside
the tree and the other half from near the outside of the
canopy.
- Sample from random trees that are representative of the
entire block.
- If you detect 2 or more infested clusters in the first
20 to 30 samples or more than 3 in the first 100 clusters
examined, treatment is advised.
- If you detect no infestation after examining 50 clusters
treatment is probably not necessary.
These leafroller sampling methods have not been evaluated
here in Whatcom County in apples but similar procedures are
used to scout for this insect in raspberries. Due to the
direct fruit damage potential from even low populations of
leafrollers at this time of the year, many growers apply
Bacillus thuringiensis (Bt) at the pink and bloom stage to
protect fruit. This timing is well suited to control overwintering
larvae in the spring. Sampling as described above should
be considered, because winter survival of OBLR larvae, and
therefore damage potential and need for treatment, can vary
significantly from year to year.
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