The traditional methods of weed control in flower plantings consist
of manual cultivation, hand pulling and mulches. However, in recent
years chemical companies have introduced a number of herbicides for
the home gardener. These weed killers have been formulated and
packaged by lawn and garden supply firms and sold through garden
centers, hardware stores and other businesses dealing in garden
products.
Classification
Generally, herbicides are categorized for use as post-emergence or
pre-emergence. The former refers to products sprayed directly on the
weed. These types, such as liquid 2, 4-D and Amitrol-T, cannot be
used safely in flower gardens due to the likelihood of injury to
desired plants. Pre-emergence herbicides are applied to the soil
before germination of weed seeds. This type of herbicide kills
germinating seeds or young seedlings but will not affect existing
weeds. Pre-emergence herbicides will be the subject of the remainder
of this fact sheet.
Proper Selection Important
At this time no herbicide will control all weeds, nor is one safe to
use around all flowers. The user must read the label and follow
directions with respect to type of weeds that will be controlled and
ornamentals tolerant of the herbicide. Too often, applicators believe
that once an herbicide has been applied, all weeds will be
controlled. This is usually not true, particularly with perennial
weeds such as dandelion, bindweed, quackgrass and thistle. Select the
herbicide for your yard depending on weeds normally present and
flowers to be grown.
Cultural Factors
Several cultural factors are important for successful results with
pre-emergence herbicides. Knowledge of one's soil type is helpful.
Certain products, such as those containing trifluralin and oryzalin,
are more effective in lighter, sandy soils, while chloramben is most
active in clay loam soils. The soil should be moist before
application or the application followed by rain or irrigation.
Herbicides applied to dry soils without rain or irrigation for 7 to
10 days will often fail as weeds will germinate before the herbicide
becomes active. The soil should be weed free at the time of
application and preferably freshly tilled, cultivated or hoed.
Effectiveness of herbicides is improved if the product can penetrate
the soil with water 1/2 to 1 inch deep. Mulching following
application of an herbicide enhances effectiveness. Should some weeds
germinate prior to the expected weed control period of four to eight
weeks, shallow cultivation can be done. Cultivation or hoeing up to
2 inches deep often extends the weed control period; however, avoid
disturbing the soil more than 2 inches or the weed killer becomes too
diluted within the soil.
Application
Most herbicides are suggested for use on an area basis. Thus, it's
important to know about how much area is included in the beds to be
treated. Once the area has been calculated, weigh or determine the
amount of herbicide needed for a bed and apply with the equipment
suggested on the label. In certain instances, it's advisable to rent
sprayers or granular applicators from tool rental agencies rather
than applying with equipment that cannot be calibrated properly.
Always make certain all application equipment is calibrated properly
prior to use. Following use, thoroughly clean the herbicides from the
equipment.
Recommended Herbicides
The underlined products represent one trade name; there may be many
for each product. In parentheses is the common name, which must
appear on the label. If the trade name listed is not available, ask
for it by its common name. For example, DCPA at one time was the
ingredient in 24 products, Dacthal being just one.
- Betasan or Lescosan (Bensulide): The granular form is recommended to
control annual grasses. Incorporate and irrigate after application
Registered for use with 24 herbaceous plants.
- Dacthal (DCPA): Wettable powder and granular forms available to
control annual grasses and some broadleaf weeds. Recommended for use
with 62 types of flowers.
- Devrinol (Napropamide): Excellent for cool season weed control in
spring and autumn. Use with aster, chrysanthemum, dahlia, daisy,
geranium, gladiolus, petunia, zinnia and daffodils.
- Eptam (EPTC): Incorporate 6 inches deep before planting to control
annual weeds and possibly some perennial weeds. Safe to use with
alyssum, ageratum, amaranths, aster, balsam, begonia, chrysanthemum,
dahlia, daylily, dianthus, nasturtium, marigold, pansy, petunia and
zinnia.
- Furloe Chloro IPC (Chloropropham): This compound is especially
effective in controlling annual grasses, chickweed and dodder. It is
recommended for 23 herbaceous plants, including bulb, corm and
tuberous crops such as daffodil, dahlia, dutch iris, gladiolus, lily
and tulip.
- Surflan (Oryzalin): Controls annual grasses, chickweed, purslane,
lambsquarter and pigweed. One-half inch of water is necessary to
activate the herbicide following application. It is labeled for
begonia, mums, gazania, geranium, impatiens, marigold, pansy, petunia
and zinnia.
- Treflan (Trifluralin): Best against annual grasses in sandy soils.
Apply before planting and incorporate 2 to 3 inches in soil. Labeled
for more than 40 flowers.
Reminders
- Thoroughly read the label and follow directions. Do not use on
vegetables, turf or other crops not on the label.
- As a result of varying environmental conditions, herbicides do not
always result in the same degree of control each year.
- Pay particular attention to timing and apply as directed before
planting or following the suggested period of establishment.
- A trial plot in a small section of the flower garden is suggested
the first time herbicides are used.
- If herbicides are spilled on skin, wash thoroughly with soap. If
swallowed, in contact with the eyes or absorbed to the point or
showing symptoms, call a doctor immediately.
NOTE: Disclaimer - This publication may contain pesticide
recommendations that are subject to change at any time. These
recommendations are provided only as a guide. It is always the
pesticide applicator's responsibility, by law, to read and follow all
current label directions for the specific pesticide being used. Due
to constantly changing labels and product registrations, some of the
recommendations given in this writing may no longer be legal by the
time you read them. If any information in these recommendations
disagrees with the label, the recommendation must be disregarded. No
endorsement is intended for products mentioned, nor is criticism
meant for products not mentioned. The author and Ohio State
University Extension assume no liability resulting from the use of
these recommendations.
-----------------
All educational programs conducted by Ohio State University Extension
are available to clientele on a nondiscriminatory basis without regard
to race, color, creed, religion, sexual orientation, national origin,
gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and
Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868
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