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March 6-20, 2000
C.O.R.N. 2000-6
In This Issue:
A)
Weed
Control in Wheat
B) Weed
Control in Alfalfa
C) Inspect
Fields for Winter Annual Weed Hosts of Soybean Cyst Nematode
D) Results
From Soybean Cyst Nematode Sampling Program, 1999-2000
E) Too
Early to Seed Forages
F) Evaluating Forage Stands, Winter
Survival and Other Tips
Wheat as a rule is very competitive
with weeds and some wheat fields do not require herbicide treatment. However,
other fields can benefit greatly from herbicide application. Failure to scout
fields and take the appropriate measure can result in yield loss and harvesting
problems in these fields. The weeds that appear above the wheat canopy late in
the season, such as ragweeds and Canada thistle, can often be easily controlled
with a spring herbicide treatment.
Many wheat herbicides have some
activity on Canada thistle and can suppress it enough to prevent harvest
problems. Effectiveness often depends upon the size of the thistle at the time
of application - regrowth is more likely when thistles are very small at time of
application. Best products for thistle control are Stinger, Curtail, and
Express.
The mild fall weather allowed many
winter annual weeds, such as chickweed and field pennycress, to get established
in many fields and they are now growing rapidly.
These weeds can interfere with the early spring development of wheat.
Winter annuals are more easily controlled when small and still in the rosette
stage, before the stem has bolted. Best products for wild garlic are Harmony
Extra and Peak, but 2,4-D also has some activity on garlic.
When wheat has not yet reached the
jointing stage, any herbicide labeled can be safely applied. As wheat growth
stage advances past jointing and then past boot stage, the herbicide choices
become much more limited. Most herbicides can be applied in nitrogen fertilizer
solution when the wheat is top-dressed. This may increase injury somewhat, and
some labels recommend adjusting surfactant rates to minimize injury. Some key
herbicide limitations are listed below - these are also shown in a figure on
page 104 of the 1999 OSU Weed Control Guide and in the text on pages 97-103 or http://ohioline.ag.ohio-state.edu/b789/index.html.
2,4-D: all 2,4-D products are
labeled for application before jointing. A few are labeled up to early boot
stage. 2,4-D is generally safe up to early boot, but the risk of injury
increases after jointing. To minimize the risk of injury after jointing, use
water as the carrier and do not apply more than 1/2 pint of ester or 1 pint of
amine. 2,4-D will not control chickweed or henbit, and can be weak on smartweed.
MCPA products have characteristics and labeling similar to 2,4-D products.
Banvel: Apply before jointing.
Not as effective as 2,4-D on mustard species, but more effective on smartweed.
Weak on chickweed, henbit, and wild garlic. Can be tank mixed with 2,4-D.
Buctril/Moxy: Apply before the
boot stage. Applying in fertilizer solution increases leaf burn. Weak on most
winter annuals, dandelion, and wild garlic.
For best results apply before weeds reach the 4-leaf stage or a height of
2 inches.
Curtail: premix of 2,4-D plus
Stinger. Apply until jointing. Excellent control of ragweeds and Canada thistle.
Weak on chickweed, henbit, and wild garlic. Do not plant double crop
soybeans in fields treated with Curtail.
Harmony Extra: Apply before flag
leaf is visible and when weeds are less than 4 inches tall or across (rosette).
Apply with nonionic surfactant. Effective for wild garlic. Weak on ragweeds.
Express: Apply before the flag
leaf is visible when weeds are less than 4 inches tall or across (rosette). Not
as broad spectrum as Harmony Extra, but more effective on Canada thistle. Apply
with nonionic surfactant.
Peak: Apply before 2nd node is
detectable in wheat stem elongation, and when weeds are 1 to 3 inches tall. Do
not plant double crop soybeans in fields treated with Peak. Apply with crop oil
concentrate or nonionic surfactant.
Stinger: Best suited for spot treatment due to high cost. Effective for Canada thistle and ragweeds, primarily. Apply up to early boot.
Like wheat, alfalfa and other forages
compete well with weeds, and proper establishment and management go a long way
toward keeping weeds under control. Some
general reminders on weed management in forages (from the Penn State Weed
Control Guide):
Establishment and seedling year:
weeds that emerge with the crop are generally more destructive
maintain the forage relatively weed-free for the first 60 days
weeds that emerge beyond 60 days will not influence that year's forage yield
later-emerging weeds may still influence forage quality
winter annual weed competition in early spring is most damaging to forages
broadleaf weeds are generally more
competitive against legumes than grassy weeds
Established stands - factors that
should influence decision to use a herbicide:
thin or irregular stands do not thicken once weeds are removed. Be sure there are sufficient desirable species to fill in the gaps. A minimum of five alfalfa plants per square foot should be present (another way to look at this is that yield will not be limited by stand if there are at least 55 stems per square foot - stands with 40 to 55 stems can still be productive)
weeds tolerant of the herbicide may invade the space left by more susceptible species, ultimately creating a more severe weed problem.
treat only well-established, vigorous stands with herbicides.
if the forage stand is at least 2 years old and 25 to 30% of the plants are weeds, removing them with an herbicide is of questionable value.
if 50% or more of the plants are weeds,
it is time to rotate to a different crop.
At this point in time, winter annuals such as chickweed are present and thriving in many forage fields due to our warm fall and recent warm weather. New forage growth has occurred in many fields also, which limits herbicide choices for winter annual control. Do not apply Gramoxone, Sencor, or Sinbar to fields where new growth has started. Velpar can be applied to established stands with no more than 2 inches of new growth (take note of the long recrop restrictions before using Velpar). Pursuit and Butyrac are probably the best options for winter annual control in fields where new forage growth has occurred.
Butyrac is weak on chickweed and
henbit, but is effective on small weeds in the mustard family (pennycress,
shepherds purse, mustards). Weeds should be no more than 2 to 3 inches tall,
and rosettes should be no more than 2 inches in diameter for best results.
Butyrac can be used on established or new stands of alfalfa, clover,
and birdsfoot trefoil. Do not use on sweet clover.
Butyrac should not injure grasses in the stand.
Pursuit should be applied when alfalfa
is in at least the 2nd trifoliate stage, but before alfalfa growth exceeds 3
inches to allow for adequate spray coverage on weeds.
Apply when weeds are 1 to 3 inches tall, or before rosettes exceed 3
inches in diameter. Pursuit may
cause injury to small forage grasses - we do not have data on grass
tolerance.
Buctril
is less effective for winter annuals than Butyrac and Pursuit, but can be
effective on mustards if small (rosettes less than 1 inch in diameter).
Alfalfa should have at least 4 trifoliates. Buctril can cause crop
leaf burn. Do not apply when
temperatures will exceed 70 degrees on the day of and for three days
following application.
A
study conducted recently at OSU indicated that four winter annual weeds common
throughout Ohio are alternative hosts of Soybean Cyst Nematode (SCN).
The weeds identified as SCN hosts are purple deadnettle, henbit,
shepherd's-purse, and field pennycress. Purple
deadnettle is an exceptionally good host of races 1 and 3 SCN and is common in
no-till crop fields, fencerows, and roadsides. As
winter annuals, these weeds will germinate in the late summer or early fall,
overwinter in a dormant condition, then resume growth and set seed in the
spring.
Shepherd's-purse and field pennycress may also germinate in early spring and complete their life cycle in 6-8 weeks; however, they are relatively weak SCN hosts compared to purple deadnettle and henbit, which mostly germinate in the fall in Ohio.
As
alternative SCN hosts, weeds support SCN feeding and reproduction in infested
fields regardless of what crop is being grown.
Consequently, SCN populations in weedy fields may stay high even when
non-host crops or SCN-resistant soybean varieties are grown in SCN-infested
soils.
We recommend that special consideration be given to controlling winter annual weed hosts of SCN in the fall, within 3 weeks after most of plants germinate but before SCN can complete a life cycle on the newly germinated seedlings. In most of Ohio, this timing would correspond to mid-September through mid October.
In
addition, host weeds that are present in the spring should be controlled early,
before corn and soybeans are planted. This is because SCN resumes activity in
the spring at about the same minimum soil temperatures for corn and soybean
planting to begin (>50 degrees). The
four SCN-host weeds identified can be effectively controlled in the fall or
spring when small with 2,4-D (1 pint/acre), Roundup/Glyphomax (1 pint/acre), or
Touchdown (2/3 pint/acre). Larger weeds may be more easily controlled with
combinations of glyphosate plus 2,4-D. Where
perennial weeds are also present, apply higher rates of Roundup or Touchdown as
recommended by the herbicide label.
More
information on SCN is available on the web at http://ohioline.ag.ohio-state.edu/ac-fact/0039.html
and at http://www.ag.ohio-state.edu/~ipm/.
The soil sampling program for soybean cyst nematode continued through the autumn and winter, 1999-2000. The Ohio Soybean Council has funded this program with soybean checkoff funds.
A total of 3,680 samples were processed during 1999. Results of the sampling are given below, in eggs/200 cc soil:
| Infestation Level | # Samples | % Samples |
| None
Detected (0) |
1,646 | 44.7% |
| Trace (40-199) |
821 | 22.3% |
| Low (200-1999) |
655 | 17.1% |
| Moderate (2000-4999) | 261 | 7.1% |
| High (5000+) |
297 | 8.1% |
During
the sampling program, one additional county, Monroe County, has been added to
those known to be infested with soybean cyst nematode.
Results
of soybean cyst nematode sampling reported by county have been continuously
updated and posted on the Web at: http://www.ag.ohio-state.edu/~ipm/scn/scn3_9.htm.
Additional information about the soybean cyst nematode can be found at the site:
http://www.ag.ohio-state.edu/~ipm/scn/scn.htm
The
backlog of samples received during the fall and winter has been processed at
this point in time and results should be in the hands of sample submitters.
New samples can still be submitted and will continue through spring of
2000.
With
the recent warm weather and dry soil conditions, some people have asked about
seeding forages now. Small grains (oats) can and should be seeded now for either
forage or grain, but it is still too risky to seed perennial forages at this
early date. Most forage crops; especially legumes are quite sensitive to below
freezing temperatures during the early seedling stages.
For
example, alfalfa seedlings are quite sensitive to frost injury until 4 or 5
leaves have formed. Wait until the last 7 to 10 days of March before planting
perennial grasses or clovers, and until the last week of March before even
considering planting alfalfa. If soil conditions are fit the last week of March,
and warm temperatures are still with us, do not hesitate to plant alfalfa at
that time, especially in central and southern Ohio.
There
is always the risk of frost injury with timely planting, but planting legumes
now in early March is just too risky, despite the current warm weather pattern.
So just hold on to the horses for two or three more weeks. Hopefully we will get
some needed rains before then followed by good soil and weather conditions for
timely early planting the last of March and early April.
With
the recent warm weather, forages are beginning new spring growth. Now is a good
time to walk hay fields and pastures to assess stand density and winter
survival. New growth in alfalfa and grass stands ranges from 1 to 3 inches
already, depending on the location and vigor of the stand. In grass hay fields,
the new growth is not as obvious, but grass growth is beginning. So the next
week or two should provide a good opportunity to assess stands.
At
this stage, established forages appear to have survived the winter very well. No
reports of heaving damage in established alfalfa stands have been received --
most likely a result of the dry soil conditions and lack of much freezing and
thawing action. Good snow cover during the coldest periods, and the dry fall
conditions most likely increased the degree of cold hardening in forages.
Winter
survival of new seedings made last summer may be much more variable, due to the
dry fall conditions which hampered growth and development. One report of heaving
in an August seeded alfalfa stand, and another report of heaved timothy seeded
with wheat has come into OSU. Heaving greater than 1/2 to 1-inch in new seedings
is serious. Such heaved plants will probably die eventually in the coming
months.
Chickweed
and other winter annuals are usually a real problem in late summer seedings with
poor vigor. So walk those fields and be prepared to make necessary herbicide
applications this week or next, before the winter annuals get too big.
As
forage stands greenup, walk your fields and estimate the number of live plants
per square foot. Actual counts in several spots can be made with a 2 x 2 foot
square, or if the planting is in rows, measure off a known area and make plant
counts. Second year stands should have 8 to 12 plants per square foot, and third
year or older stands should have 5 to 6 plants per square foot for optimal yield
potential. Estimated the ground cover of desirable forage plants can also be
estimated visually. This should be done when there is about six inches of
growth.
Stands
with more than 80% ground cover will produce excellent yields. Stands with
60-80% ground cover should produce fairly normal yields. Stands with 40 to 60%
ground cover will probably produce yields in the 60% range of normal. Stands of
20-40% ground cover will yield less than half their normal hay potential. Weeds
will become real problems in the thinner stands, and overseeding with grass or
destroying the stand and rotating out should be considered.
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Contact your local Ohio State University Extension Office or e-mail
Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/
C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
Special
thanks to Kent Harrison, Department of Horticulture and Crop Science and Nancy
Taylor, Plant Pest Diagnostic Clinic for contributing to this edition of CORN.
Contributors to C.O.R.N. include:
State Specialists: Pat Lipps & Anne Dorrance (Plant Pathology), Hal Willson
(Entomology), Peter Thomison (Corn Production), Jay Johnson (Fertility), Jim
Beuerlein (Soybeans & Small Grain), Mark Loux (Weed Science), Jeff Stachler
(Weed Science), Mark Sulc (Forages)
Editor: Greg LaBarge Web Editor: Nathan Watermeier
Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
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.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
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