Weed Control in Home Gardens - Chemical Weed Control

Chemical Weed Control

Chemicals (herbicides) are only occasionally used by
home gardeners to control weeds because suitable herbicides
are seldom legally available in small, economical
amounts.
There are also several other diffi culties with the use of
herbicides by home gardeners. Many herbicides are nonselective
and will kill the vegetables, as well as the weeds.
Others are selective and can be used only with certain
vegetables or control only certain weeds. Home gardens
generally contain many vegetable and weed species, which
makes using selective herbicides diffi cult. Some herbicides
may also damage nearby vegetables or remain in the soil
and damage future plantings.
Even if available and effective, herbicides may not be
legal for use on a specifi c vegetable or at the time when
they are needed. The herbicide application rate may be very
low and extreme accuracy in application may be absolutely
essential. Overlapping applications may kill vegetable crops
and, if areas are skipped, weeds will not be controlled.
Required pre-harvest intervals (PHI's) or waiting periods
between application and harvest can be lengthy and must
be observed. Herbicides may also be effective only for a
short period of time or produce results slowly.
Despite all these problems, there are occasions when
herbicides may be successfully used in home gardens. The
following suggestions will assist home gardeners in effectively
using herbicides.
1. Understand the difference between preemergence and
postemergence herbicides. Preemergence herbicides are
effective only before weeds germinate. Postemergence
herbicides work on weeds that are actively growing.
2. Understand the different formulations of herbicides
available and how the formulation affects use. Some of
the more common formulations are emulsifi able concentrates
(EC), fl owables (FL), wettable powders (WP)
and dry fl owables (DF). All are designed to be mixed
with water and sprayed on the area to be treated. Wettable
powders and dry fl owables may settle out unless
the sprayer is shaken periodically. Herbicides may also
be formulated as granules (G). These are to be spread
evenly over the soil surface.
3. Plan the garden in detail. Plan to locate all the crops for
which a specifi c herbicide may be used near each other.
This allows treatment of larger areas with less effort.
4. Follow all instructions on the label. This is extremely
important. Failure to follow the label instructions
precisely may result in harm to the applicator, the environment
or the crop. Preemergence herbicides require
weed-free soils without lumps or clods. Most are best
applied to moist soil and shallowly incorporated by tilling,
irrigating or natural rainfall. They must be applied
uniformly and at the proper rate to be safe and effective.
Postemergence herbicides may be applied over the top
of the growing crop and weeds. Again, it is essential
that all aspects of the label directions be understood and
followed. If you have any questions, consult your county
Agricultural Extension agent.
5. Rinse spray equipment. Residual herbicide in sprayers
may damage crops. Many gardeners who use herbicides
purchase spray equipment for herbicides only and keep
it separate from equipment used for insecticides and
fungicides.
6. Calibrate application equipment accurately. Inaccurately
applied herbicides may be ineffective or dangerous. If
there is a question on how to apply a specifi c herbicide,
contact your local county Agricultural Extension offi ce.
The two most suitable herbicides for use on home gardens
are Trifl uralin (Trefl an™) and Sethoxydin (Poast™).
Trifl uralin is sold in many formulations, each designed
for specifi c uses. Trifl uralin prevents the germination of
most grasses and some broad-leaved weeds (for several
weeks) and must be applied before these weeds germinate.
Sethoxydin kills growing grasses. It requires only a short
waiting period between application and harvest and may be
applied to a wide range of vegetables.
Proper use of herbicides may involve grouping vegetables
according to the herbicide that may be applied to them,
as well as paying attention to rate, timing, uniformity and
method of application. Remember, label directions must
always be read and followed.
SP291I-5M-6/03(Rev) E12-5115-00-021-03
The Agricultural Extension Service offers its programs to all eligible persons regardless of race,
color, national origin, sex, age, disability, religion or veteran status and is an Equal Opportunity Employer.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
The University of Tennessee Institute of Agriculture, U.S. De partment of Agriculture,
and county governments cooperating in furtherance of Acts of May 8 and June 30, 1914.
Agricultural Extension Service Charles L. Norman, Dean
The Stale Seedbed Technique
The stale seedbed technique is a system that controls
weeds prior to the planting of the crop. The theory is that
most weed seed that germinate are found in the top 2 to 3
inches of soil. With soil temperatures of 70 degrees F or
higher and moist soil, most of the weed seed in the top 2
inches of the soil will germinate in 2 to 4 weeks after a tillage
operation. Therefore, a generalized procedure follows.
1. Broadcast fertilizer and incorporate with a final tillage.
2. Allow the weed seed to germinate for 2 to 4 weeks.
3. Once most of the weeds have germinated, kill the
emerged weeds. This can be done by using a nonselective
herbicide such as glyphosate (Roundup) or by
performing a shallow tillage (less than 2 inches).
4. Then seed or transplant the crops with minimal soil
disturbance.
Since warm soils are required for this technique to
be effective, it generally is not used for spring-planted
gardens. It can be very effective when utilized prior to the
planting of a fall garden.

Weed Control in Home Gardens - Cultural Weed Control

Cultural Weed Control
Most cultural methods of weed control emphasize prevention.
These include mulching, solarization, and multiple
or wide-row planting.
Mulches
Any layer of material spread over the soil surface
may be considered to be a mulch. There are two classes of
mulch: organic and inorganic. Both reduce weed growth,
retain soil moisture and influence soil temperature.
Hay, straw, sawdust, ground bark, leaves, compost and
even newspapers are among the many substances utilized
as organic mulches. All reduce weed emergence and make
it easier to pull those weeds that do emerge. Some weeds
such as nutsedge will grow through mulch, even through
plastic mulch. Extension factsheet SP 291-H,
Mulching
Vegetable Gardens, contains additional information regarding
the use of mulches in home gardens.
Inorganic mulches include black and other opaque plastic
as well as landscape fabric. Landscape fabric is much
more expensive than plastic mulch. However, it has the
advantage of allowing water to pass through into the soil.
Black plastic (polyethylene) is the most commonly used
inorganic mulch. Clear or translucent plastic should not
be used as mulch. These plastics allow light to penetrate,
which permits germinated weed seed to grow under the
plastic mulch. Black plastic eliminates growth of most, but
not all, weeds. For example, yellow nutsedge will grow
through plastic mulch. Also, weeds will grow in the holes
cut in the plastic for the vegetables. More information regarding
the proper time and method of application, as well
as the advantages and disadvantages of plastic mulches, just search below.
Opaque plastic in colors other than black is sometimes
used as mulch and will also control weeds. However, many
of these plastics are quite expensive. Some data suggests
that tomatoes grown on red plastic or that muskmelon
grown on blue plastic will produce higher yields. Yield
increases of up to 25 percent have been documented. However,
the results are not consistent enough to justify the
expense of the colored plastics.
Due to high temperatures and intense solar radiation,
the use of black plastic may cause damage to plants transplanted
or seeded during the hottest part of the summer.
White plastic can be utilized during the summer months to
prevent root and stem damage to the plant. White plastic
will allow light to penetrate. Therefore, white plastic with
a black backing (known as white on black) is preferable.
White on black plastic is more expensive and may be diffi
cult for home gardeners to locate in affordable quantities.
Another option is to whitewash or paint the black plastic
with white latex paint. The paint will eventually wear off,
but not until the plants have shaded the plastic around the
base of the plant, reducing the chance of damage.
Solarization
Solarization is the use of clear polyethylene plastic
sheeting (2 to 6 mils thick) to capture the radiant energy of
the sun, thereby raising the soil temperature to levels lethal
to many weed seeds. The plastic sheeting is placed over
bare, moist soil during a summer fallow period. In Tennessee,
best results are obtained by using two layers of plastic
sheeting and separating the layers with boards, bricks or
small squares (ca. 3” X 3”) of polystyrene insulation called
spacers. Spacers are placed every 1.5 to 2 feet on top of the
fi rst layer of plastic. The second layer of plastic sheeting is
then placed on top. This creates an air gap between the two
layers, which provides a reservoir of warm air that minimizes
nighttime cooling. The two layers of plastic sheeting
are then sealed together by placing soil along the outer
edges of the top layer.
The top layer of plastic should be kept clean to maximize
solarization effi ciency. An occasional dusting with a
dust mop or rinsing with a garden hose should be all that
is necessary. The plastic is left in place for 4 – 5 weeks.
During this period, soil temperatures are frequently raised
to 120 – 125 degrees F. This practically eliminates viable
weed seed in the top 2 to 3 inches of soil. After the plastic
is removed, care must be taken not to mix the deeper layers
of unsolarized soil with the nearly weed-free solarized soil.
Rototilling no deeper than 1 – 2 inches is recommended.
As long as the soil is not rototilled deeper than this, weed
control by soil solarization can signifi cantly reduce weed
infestations for 12 months or more. Many soil-borne plant
pathogens will also be reduced during the solarization process.
This improves plant stands and vigor and may double
yields.
The best time to solarize soil in Tennessee is from May
through early August. Two or three periods, each consisting
of several days in a row of warm weather and bright sunshine,
are necessary. Late summer and fall vegetables may
be planted the day after removing the plastic.
Multiple or wide row planting
Closely spaced double or triple rows may also assist in
weed control. Simply plant two or three rows of a vegetable
close enough so that the leaves will cover the area between
them rapidly as the plants grow. Very small vegetables such
as radishes may be broadcast in a long row a foot or so
wide. These techniques allow growing vegetables to shade
the soil, which reduces weed growth.

Weed Control in Home Gardens - Mechanical Weed Control

Mechanical weed control:
Mechanical weed control involves removing weeds
while they are small and preventing them from producing
mature seed. It consists principally of mowing, ploughing,
rototilling, hoeing and hand pulling. These procedures
give immediate results and require little, if any, specialized
equipment. Their main disadvantage is that they work only
on growing weeds and may need to be repeated frequently.
Remove weeds while they are small because it is
quicker, easier and does less damage to desired vegetable
plants. Hoe or till shallowly (less than 2 inches deep) to
avoid damage to desirable plants and to minimize moisture
loss from the soil. The deeper the soil is disturbed, the
more weed seed will be brought to the surface where it will
grow. Most weed seed that germinate are in the upper 2
inches of soil. Weed seed may survive many, many years in
the soil. Each time it is worked, more seed is pulled to the
surface.
Gardeners often quit weeding as a crop matures. Weeds
do not affect crop yields as much at this stage. However,
they will still produce seed. A single weed of some species
can produce hundreds of thousands of seed. Weed removal
should continue until the vegetable crop is completely harvested.
While crops are not growing on the garden spot, the
soil may then be kept tilled, mowed or heavily mulched to
prevent weeds from propagating. Frequent tillage has the
additional advantages of turning organic material under
where it will add to soil organic matter and of mechanically
destroying any insects that are present.

What is a weed, How do weeds harm gardens and Why are weeds hard to control?

What is a weed?
A weed may be broadly defined as any unwanted plant,
or as I have heard it said many times, “a weed is a plant out
of place.” For example, a corn plant is a weed if it is in a
strawberry planting. Most weeds are plants that are generally
considered undesirable by gardeners. They are neither
eaten nor considered attractive. They are frequently invasive
and difficult to control.
How do weeds harm gardens?
Weeds compete with crop plants for moisture, nutrients
and light. They may also harbor insects that harm flowers
or vegetables or transmit diseases to the crop. Weeds can
also serve as alternate hosts for diseases. They also promote
diseases by increasing humidity, decrease vegetable
quality and make harvests difficult. Vegetable plants grown
under weedy conditions will have reduced yields, or they
may not survive to produce at all. A weedy garden or flowerbed
is also unattractive.
Why are weeds hard to control?
Weeds are highly adapted to where they grow. They
have large, efficient root systems, grow rapidly and frequently
produce tremendous amounts of seed. Most weeds
tolerate drought and low fertility. Little of their energy is
used producing lush foliage, large seed or fruit. Therefore,
they often thrive where vegetables struggle to produce.
Many spread rapidly by vegetative structures as well as by
seed. The principle methods of weed control fall into three
categories: (1) mechanical, (2) cultural and (3) chemical.