Weed Control Guide for Ohio Field Crops
Bulletin 789
Control of Problem Weeds
Winter Annuals
Many winter annual weeds, including common chickweed, purple deadnettle,
henbit, and cressleaf groundsel, have become increasingly problematic in
corn, soybean, and wheat production. These weeds emerge primarily in
the late-summer through fall (and sometimes early spring), overwinter,
and flower and set seed in late spring or early summer. They can
directly interfere with wheat establishment and growth in the fall or
spring. While they do not necessarily compete directly with corn and
soybean growth, winter annuals cause a number of other problems,
including some of the following:
- the dense mat of chickweed and other winter annuals can slow
soil drying and warming and interfere with planting and tillage in
the spring
- harbor insects in the spring, which later infest corn or
soybeans
- purple deadnettle and several other winter annuals appear to
serve as alternate hosts for soybean cyst nematode
The goals of a winter annual management programs should be control with
herbicide or tillage in the fall or early spring to: 1) prevent problems
with crop establishment; 2) prevent problems with pests associated with
winter annuals; and 3) prevent additional winter annual seed production.
Fall herbicide treatments are an extremely effective tool for managing
winter annual weeds, and fields where these weeds have been a problem
over the past several years should be considered as good candidates for
fall herbicide treatments. Some general suggestions to maximize
effectiveness of these treatments follow:
- Optimum time of application for control of emerged winter annuals is between mid-October and mid-November. We have applied as late as the first week of December under very cold conditions, and still achieved effective control. However, we suggest applying herbicides under relatively warm conditions if possible.
- When using residual herbicides (Canopy, Backdraft, Python, etc) with the goal of controlling weeds as long as possible into the following crop, delay application until November to minimize herbicide degradation.
- We recommend including 2,4-D with all treatments, to reduce the risk of herbicide resistance and help control dandelions and a few other weeds. A rate of 1 pint/A should be adequate with most treatments.
- Treatments with glyphosate should be applied with ammonium sulfate. Include surfactant if recommended by the glyphosate product label. Most other treatments should be applied with crop oil concentrate.
- If possible, wait a minimum of a week or so after crop harvest to apply herbicides, which allows time for crop residue to settle and maximizes contact of spray with weeds.
Ohio State and Purdue University have conducted studies on the
effectiveness of fall herbicide treatments over the past several years,
and the following treatments have been among the more effective in this
research.
- Glyphosate or glyphosate plus 2,4-D: Very effective treatment
for control of dandelions and winter annuals. Can be used prior to
corn or Soybeans. Primary disadvantage is the lack of
residual activity into the following spring, which means that two
in-season herbicide applications are likely to be necessary. The
minimum rate for glyphosate applied alone in fields with dandelion,
wild carrot, and other simple perennials and biennials should be
0.75 lb acid equivalent per acre. When applied with 2,4-D, the
glyphosate rate can be reduced to 0.38 lb ae/A unless the population
density of these species is extremely high or other perennial weeds
are present.
- 2,4-D (1.0 lb ai/A): Economical treatment for dandelion and
most winter annuals, but will not control chickweed. Can be used
prior to corn or Soybeans. Primary disadvantage - no residual
activity into the spring. Populations of wild carrot can be
resistant to 2,4-D, and control of these will be unacceptable.
Cressleaf groundsel and curly dock may not be completely controlled,
because they have tolerance to 2,4-D.
- Backdraft (glyphosate plus Scepter) plus 2,4-D: Similar to
glyphosate plus 2,4-D, with the addition of residual activity into
the following season (but shorter period of residual control on
ragweeds compared to CanopyXL). Scepter appears to antagonize the
glyphosate/2,4-D occasionally, reducing control of dandelion
primarily. Use before soybeans only.
- Canopy XL plus Express plus 2,4-D: Effective treatment for
dandelion and winter annuals. Provides residual activity into the
following season the length of this residual varies with rate of
Canopy XL applied. Disadvantage possibility of developing ALS
resistance (so use of 2,4-D with this treatment is essentially
mandatory) and lack of control of ALS-resistant marestail in the
spring. Use before soybeans only. Low rates of Canopy XL may not
completely control 2,4-Dresistant wild carrot.
- Sencor plus 2,4-D: Effective on many winter annuals, but
rarely provides more than 80% chickweed control in OSU studies
(usually conducted in very dense chickweed areas). Sencor appears to
antagonize the 2,4-D on dandelion, reducing the control. Sencor does
not control wild carrot. Expect shorter period of residual control
on ragweeds compared to CanopyXL or Scepter. Can be applied in fall
before corn or Soybeans.
- Simazine plus 2,4-D: Effective on winter annuals and
dandelion, but a 2,4-D rate of 1 quart/A may be necessary for
effective control of dandelion and large purple deadnettle in
problem fields. Use in the fall before corn only.
- Basis plus 2,4-D: Controls winter annuals and danderlion. Use
in the fall before corn only.
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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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