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* Spider
Mites
* Raspberry
Crown Borer
* Plant Parasitic Nematodes |
* Cane
Blight
* Phytophthora
Root Rot |
Biology
Spider Mites (Decison
Making Guide) (Images)
Spider mite populations can increase rapidly after harvest through
early September. Most of the mite population by this time has moved gradually
from fruiting cane to primocane foliage. Under certain conditions in the absence
of mite predators, spider mite populations can reach up to 300 mites/leaflet
by late August, but this is not typical. There is no clear correlation between
mite population density and economic injury to raspberry fields. Recent research
indicates the importance of maintaining healthy foliage late into the season
in order to provide adequate carbohydrate reserves for the plant. With this
in mind, it is good management to monitor spider mite populations through early
September. Overwintering mites who become more orange in color begin to migrate
from the leaves in mid- to late- September.
Raspberry
Crown Borer (Decision
Making Guide) (Images)
Adult crown borers can be present in raspberry fields from late
July through early October. They look like a black and yellow wasp,
but are actually a moth
with clear wings. Females produce as many as 100 eggs, which are deposited
singly on the undersides of berry leaves. Small caterpillars hatch from these
eggs, crawl down to the base of the canes, and form an overwintering cell in
the side of the cane. Second year caterpillars, which tunnel into the canes
and fleshy roots, may be present at this time of the year as well.
Cane
Blight (Decision
Making Guide) (Disease Cycle)
(Images)
Cane blight requires a wound to enter the vascular tissue of the primocane.
In fields where cane blight has been a problem, a fungicide application is
usually made immediately after harvest to suppress infection. Make sure that
the bottom half of canes receive adequate fungicide coverage. Cane blight infection
is likely to be more severe in years with heavy rainfall during the harvest
period. The canes become highly resistant to infection in the fall.
Plant Parasitic Nematodes (Decision
Making Guide)
There are two types of microscopic nematodes which can damage raspberry
fields in northwest Washington. They are root lesion nematodes
(Pratylenchus penetrans)
and dagger nematodes (Xiphinema americanum and X. bakeri). Root lesion nematodes
migrate within the roots and between soil and root tissue, whereas the dagger
nematodes stay outside of the roots, feeding on root tips. Both cause direct
damage to root tissue. One of the dagger nematodes (X. americanum) causes little
or no direct root damage but is capable of transmitting the tomato ringspot
virus which reduces raspberry growth and causes crumbly fruit. X. bakeri is
suspected to transmit viruses as well, although this has not been proven. The
presence of either species of dagger nematodes is cause for concern.
The nematodes most commonly found in raspberry fields in northwest
Washington are P. penetrans and X. bakeri.
Phytophthora (Decision
Making Guide) (Images)
The most common above ground symptom of Phytophthora root rot during
the harvest period is the collapse of fruiting laterals and wilting
of primocanes. The
pattern of diseased plants is determined by the presence and movement of the
disease organism in the soil. Root rot caused by Phytophthora fragariae var.
rubi can be found in both well-drained and poorly drained soils.
Monitoring
AUGUST - SEPTEMBER
Spider
Mites (Decison
Making Sheet) (Images)
- Examine
leaves immediately after harvest to determine population
density of spider mites and mite predators. Predators can become
quite numerous this late in the season, particularly in fields
with low insecticide use. Treatment is considered unnecessary
unless the population reaches 25 mites per leaflet by September
1.
- Sample
by collecting at least ten leaflets per site in a minimum
of four locations in the field.
- Record
the number of mites at each site to illustrate the
variation across a field and to decide which areas, if any, require
a spray.
Raspberry
Crown Borer (Decision
Making Sheet) (Images)
- Check
lower canes and crown material closely in weak areas
of a field for first or second year caterpillars, particularly
if adult crown borers are seen during the late summer months.
- October is the preferred month for treating infested fields.
Spur
Blight and Cane Blight (Decision
Making Sheet) (Images)
- Monitor cane blight in the late fall by scraping
away the epidermis on the canes near the catcher plate height.
- Look
for a brown stripe lesion spreading from a wounded area.
- Infected canes become brittle the following spring and can
be easily broken at that time.
- Monitor spur blight by looking for the characteristic chestnut
colored lesions which are associated with nodes on the primocanes.
It is too late to control the disease this season, but findings
will be useful for managing the disease the following year.
Phytophthora
Root Rot (Decision
Making Sheet) (Images)
- Soon after harvest, if you have not done so already, identify
areas which show symptoms of Phytophthora infection. These include
premature decline of fruiting canes and primocane wilt.
- Examine the crown region of suspect plants by scraping away
the epidermis. Diseased plants have red or brown rotted tissue
with a clear demarcation between the diseased and adjacent healthy
white tissue.
- There are several tactics to control this disease. They include:
- Tiling and/or ripping soil to improve drainage.
- Consider hilling or replanting into raised beds.
- Clean tillage equipment used in known Phytophthora infested
soils before moving to healthy fields.
- Apply fungicides in only those fields known to be infected
with the disease organism.
- Avoid planting raspberries in fields with a history
of Phytophthora.
- Do not introduce Phytophthora on plant material. Do
not plant root stock that has been under a suppressant
fungicide program to control Phytophthora.
Plant
Parasitic Nematodes (Decision
Making Sheet)
- Sample fields for nematodes in September. If a significant
population is found, treatments should be applied in the fall.
- Because root lesion nematodes are found within the actual
roots as well as in the soil, it is important to collect
both soil and roots when evaluating them.
- Try to take at least two samples from each field, comparing
good versus poor areas if possible.
- Each sample should represent about ten plants scattered throughout
the sample area.
- Using a shovel and pruning shears, collect a handful of soil
and feeder roots from the top foot of each plant sampled.
- Roots and soil can be placed together in a plastic bag and
shipped to the lab for analysis.
- If you are just sampling soil, use a soil sampling tube and
take a minimum of 20 - 1ft deep cores.
- A rough treatment
threshold has been established for root
lesion nematodes; it is 250/250 cc of soil (500/pint). Root lesion
counts taken from root tissue in northwest Washington have been
reported as high as 2,000 nematodes per gram of root tissue.
More typical numbers are in the 10 - 50 range. There are no thresholds
based on root analysis.
- Due to the migratory habits of root lesion nematodes, sampling
roots in addition to soil can provide a more complete picture
of the situation. There have been cases when soil populations
are below threshold, but roots are quite heavily infested. This
is most likely to occur under very dry soil conditions.
- Dagger nematodes, if present, are usually found at much lower
densities. X. bakeri is the most commonly found dagger nematode
and seems to be associated with declining, low vigor fields.
Unfortunately, these nematodes are not controlled by any nematicides
currently registered for use on established plantings. They are
most effectively controlled with chemical fumigation before raspberries
are planted
Scouting
Report - Post Harvest (PDF File)
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