- Introduction
- Weed Biology
- Best Management Practices
- Non-Chemical Weed Control
- Chemical Control: Methods of Application
Introduction
The weed flora in blueberry fields is unique compared to that
found in cultivated fields. Producers are dealing with a native
perennial crop in low pH soils, where there is no associated
tillage nor cultivation. Most of the problem weeds encountered
in low bush blueberry fields are perennials. However annual
and biennial weeds may also be present. Weeds which prefer
low pH soils and the same habitat as blueberries thrive if
not controlled.
The history of a field often determines its weed flora. Fields
developed from abandoned hayfields or pastures typically have
a large number of grasses and herbaceous perennial weeds.
Fields developed from woodland, however, often have plants
commonly associated with the woodland undergrowth such as
bunchberry, as well as perennial bushes and shrubs.
To successfully develop a weed control program, it is important
to identify the weeds, understand their life cycle and have
an appreciation of why particular weeds grow in particular
areas.
Weed Biology
The life cycle and reproductive strategy of a weed species
are important factors to consider when planning a control
program. Weeds can be classified as annuals, biennials or
perennials. Weeds can additionally be classified as grasses,
broadleaf weeds, ferns, herbaceous or woody weeds.
Annuals
Annuals complete their life cycle from seed in less than one
year. There are two types: summer and winter annuals. Summer
annuals germinate in the spring, mature, produce flowers and
seeds and die before fall. Winter annuals germinate in the
fall, overwinter in a seedling or rosette stage, mature, produce
flowers and seeds, and die in the spring or early summer.
Because of the seedling stage, annual weeds are generally
easy to control. There are usually few annual weeds present
in lowbush blueberry fields.
Biennials
Biennials generally complete their life cycle over two years.
The first year the seeds germinate and form a basal cluster
of leaves and a tap root. The plant overwinters in this stage.
During the second year the weed produces a flower stalk, sets
seed and dies. Examples of biennial weed are evening primrose
and wild carrot. Biennial weeds are rarely observed in blueberry
fields.
Perennials
Perennial weeds live for more than two years. These weeds
are the most common in blueberry fields and generally the
most difficult to control. Perennial weeds may reproduce primarily
by seed (daisy); by both seed and roots (sheep sorrel); or
primarily be vegetative means (bunchberry). Many perennial
weeds grow in the same manner as the blueberry plant. Therefore,
many of the production practices that promote blueberry growth
(e.g. pruning) also promote growth of these weeds. Perennials
which are low growing and spread vegetatively by interconnected
underground root systems are the most difficult to control.
Perennial weeds growing above the blueberries may be controlled
by wiping or spot treatments with registered herbicides. Perennial
weeds include both woody and herbaceous species.
Woody plants can be classified as any plant which develops
woody tissue. This may include brush, shrubs, trees and woody
vines. Herbaceous plants are those that are not woody.
Broadleaf Plants
Broadleaf weeds are annual, biennial or perennial plants which
generally have two leaves (cotyledons) emerging upon germination.
The leaves normally have a branching network of veins and
the flowers have distinct petals.
Grasses, Sedges and Rushes
Grasses can be annual or perennial plants. They generally
have narrow, upright, parallel-veined leaves. Grasses have
jointed stems, usually hollow at the internodes and are circular
in cross section.
Sedges are a large group of perennial (rarely annual) grass-like
plants which are common in wet, poorly drained soils. Sedge
stems are triangular in cross section, solid, and not jointed.
Rushes are annual or perennial plants similar in appearance
to sedges with grass-like tufted leaves common at the plant
base. Rush stems are hollow, circular in cross section, and
not jointed. Like the sedge, this plant is also common in
wet areas or poorly drained soil, but is also found in woodland
and open fields.
Ferns
Ferns are primitive perennial plants that do not produce flowers
and seeds. Ferns consist of a leaf or frond, a stalk and an
expanded blade which may then be further subdivided several
times. Ferns spread by long creeping rhizomes and/or by spores.
For More Information
Most weed guides do not include many of the important blueberry
weeds. However, an excellent illustrated publication for identification
of blueberry weeds is:
Weeds of Eastern Canadian Blueberry Fields,
by G. Sampson, K. McCully and D. Sampson.
Contact the Nova
Scotia Agricultural College Bookstore to purchase this
publication.
Best Management Practices
One way blueberry growers can respond to environmental pressures
in a pro-active manner is to adopt "Best Management Practices."
These are recommendations and guidelines to help growers make
sound environmental decisions in their farming operation.
They are a combination of management, cultural, and structural
practices that are considered to be effective and economical
in controlling problems without disturbing the quality of
the environment. They provide opportunities for growers to
evaluate their own operation and choose the best management
practices that are most appropriate for their own situation.
Keep in mind that many of the production and management activities
practiced by blueberry growers influence not only their own
operation, but their neighbours and community. Anything that
can prevent environmental pressures will make their own operation,
as well as the industry itself, more sustainable.
Growers should identify problems within their operation and
implement the appropriate changes. Examples of best management
practices include:
- Scout fields and spray only when and where necessary
- Match appropriate herbicide rates with soil type
- Do not apply herbicides within 50 m of bodies of water
- Do not mix or load near bodies of water, bring the water
to the sprayer
- Do not apply herbicides to rock formations and exposed
ledges as they may provide a direct channel to groundwater
- Avoid spraying if heavy rainfall or high winds are forecast
- Use a anti-backflow device when filling sprayers from
a water source to prevent contamination from backflow
- Make sure your sprayer or spreader is calibrated properly
and accurately
- Leave an untreated vegetation strip near any water sources
to act as a filter
- Read and follow all instructions as stated on the manufacturer's
current label
Non-Chemical Weed Control
Non-chemical methods of weed control have not generally been
used alone but are often used prior to or following other
treatments to further enhance control.
One common production practice used by blueberry producers
is pruning by fire or mowing. Although the main purpose of
pruning is to rejuvenate blueberry plants, it also helps control
weeds. Burning will control coniferous species and some shallow
rooted grasses. The top growth of many deciduous saplings
is generally killed by burning but underground parts may sprout
again, requiring additional control measures. Burning also
helps prevent the return of many weed seeds from mature plants
to the soil, and will kill many of the weed seeds present
near the soil surface. Frequently, however, only partial or
erratic control results. Burning or mowing alone may promote
growth of many perennial weeds with extensive underground
root system.
Mowing and cutting are useful, particularly on weeds higher
than the blueberries. Weeds must be mowed or cut several times
during the season to ensure suppression. Species such as maple,
birch and willow should be cut back to ground level. Regrowth
from the roots usually results and should therefore be cut
again. Species cut in June, July and August for a few seasons
will help ensure weed control. Cutting weeds every mid-summer
has also been found to help control bracken fern, sweet fern,
bayberry, Prunus spp., lambkill, wild rose and others.
Bracken fern should be cut just as the fronds unfold, at least
two times, at four to six week intervals. Cutting the tops
off weeds can also prevent seed production which could reduce
future weed problems. This must be done before seeds ripen.
Cutting, however, is labour intensive, and does not generally
result in permanent control.
Other practices which may help to control weeds include the
use of mulches. Wood chips, sawdust or bark mulch can reduce
weed problems, particularly on bare spots within the fields.
Planting blueberry plants in bare spots throughout the field
help bare spots to fill in more rapidly.
Preventive methods such as cleaning field equipment (mowers,
harvesters, tractors, winnow machines and boxes) also help
prevent the spread of undesirable weeds into uninfested fields.
The use of biological control agents such as Chrysolina
beetle on St. John's Wort can also help suppress weeds although
the use of this method is not compatible with most insecticides.
Chemical Control: Methods of Application
For recommendations on chemical weed control, consult
your provincial or state lowbush blueberry extension specialist
or your weed extension specialist.
There are various methods of applying herbicides to unwanted
vegetation. One should choose the method that best suits the
conditions and available equipment.
Be sure to read the information that is provided on the
label. To avoid damage to the blueberry plants, and to obtain
satisfactory control of weeds, herbicides must be applied
at the recommended rate.
Overall Broadcast Spray
An overall broadcast spary is used to treat entire fields
with a residual soil-applied herbicide after the pruning operation
and before blueberry plants emerge in the spring.
Overall broadcast spraying is done with a boom sprayer.
Irregular spray applications can be avoided by the use of
flagging tape, foam markers or the use of an appropriate dye.
To apply herbicides at the recommended rate, equipment must
be calibrated and in proper working order.
Foliar Applications on Brush
Unless otherwise stated on the label, applications should
be limited to bushes which are under 2 meters in height. If
bushes are higher, cut and treat the regrowth. Foliar applications
are generally the most effective just after full leaf development
in late spring or early summer. Applications made to actively
growing bushes will be the most effective if good growing
conditions and adequate soil moisture are present. Under those
conditions, applications may be made up to 2 or 3 weeks before
the normal frost date.
Coverage should be uniform and thorough to wet all leaves,
stems and root collars. Mix with water only and spray until
wet, but avoid spraying to runoff. Extreme caution must be
used as any spray contacting blueberry plants can cause severe
injury or death. The use of herbicide wipers and rollers can
also be useful for applying herbicides to the foliage and
stems of species which grow above the crop.
Stump Treatment (Used for site
preparation only)
Unless otherwise stated on the label, the herbicides used
for stump treatment should be applied in diesel oil, fuel
oil, kerosene or mineral oil to help penetrate the exposed
bark and cut surfaces (environmentally, mineral oil is the
preferred choice). This treatment is useful in that it can
be applied any time of the year, including the winter months
as long as snow or water does not prevent spraying. Unless
otherwise stated, applications should be made to freshly cut
stumps. Best results are usually obtained on stumps 5 cm across
or larger (refer to individual labels). All exposed bark,
roots, and cut surfaces should be wet thoroughly either by
painting or spraying. For old stumps it is best to drill several
holes or split the stump with a wedge before applying the
treatment. Dye can also be added to the mixture to help ensure
that all exposed surfaces of the stump have been treated,
and stumps do not get retreated or skipped.
Trash from brush cutting operations such as sawdust, leaves,
branches, etc. should be removed from the base of the stumps
before treating. Care must be taken to ensure that all cut
stems in a clump have been treated, or regrowth can result.
Most of the stump treatments will control the top growth of
root suckering species (i.e. poplar, and aspen), however,
regrowth from lateral roots may occur the following season.
Basal Bark Treatments
Brush and small trees (15 cm diameter) can be controlled
by spraying or wiping the basal parts of bush stems and tree
trunks from the ground line up to a height of 50 cm or as
recommended on the label. Treatments are applied in diesel
oil, fuel oil, kerosene or mineral oil as recommended on the
label (environmentally, mineral oil is the preferred choice).
Old or rough bark requires more volume than young or smooth
bark. Treatments can be applied any time of the year except
when snow or water prevent spraying at the ground line. Basal
bark treatments are advantageous because the entire bush or
tree foliage does not require spraying. If spraying, use a
nozzle that forms a very narrow band or stream.The basal bark
treatment is useful against a wide range of trees and brush
with trunk diameters up to 15 cm.
Spot Sprays
Spot spraying applies herbicide to the foliage of weed
species, avoiding contact with the blueberry foliage. Depending
on the product used and the time of application, blueberry
plants can be injured or killed if the foliage is sprayed.
Applications are often made in the summer of the sprout year,
but these can result in crop injury. Alternatively, evergreen
species, such as lambkill and bayberry, can be controlled
in the fall. Furthermore, many species such as alders, sweetfern,
bayberry, blackberries retain their leaves in a viable condition
longer than the harvested blueberries and can be treated in
October.
Spot sprays can be applied with either backpack sprayers
or by operating a handgun from a line connected to a tractor
mounted sprayer.
Wiping Treatments
Wiping and rolling methods can be used where weeds are
taller than the blueberries. A commercially available "side-swipe"
or "hockey-stick" has been used effectively for applying Roundup.
There are several roller-type applicators now in use, including
several tractor mounted models and small one-man portable
machines for use in small fields. The herbicides is slowly
delivered to a rotating drum, with an absorbent covering,
that wipes the foliage of tall weeds and bushes, transferring
the herbicide from roller to leaves. To avoid misses, most
rollers must be operated quite slowly.
Updated January 15, 2001
This page and all contents Crown copyright ©
1997, Province of Nova Scotia,
all rights reserved.
