Volume 17, No. 1
September 2001
With the season coming to a close and fall planting just around the
corner, I thought that I would devote this edition of the Maryland Weed
Reporter to items we should consider before frost. First of all, this is a perfect time to
treat perennials. Secondly, small
grains will be getting planted soon, and with the vast array of weeds we have
to contend with, there are some new tools we can use in our battle against
them.
Perennials. Fall
is a perfect time to treat perennial weeds.
Why? Because the plant is now
storing carbohydrates and sugars to allow it to overwinter. Thus, flow is from the top of the plant to
the below ground root system. By applying
a systemic herbicide to that plant, flow will also be from the top of the plant
down to the roots. While you may have
seeds to contend with next year, your major goal in the Fall is to get rid of
or at least make some inroads in destroying the underground root systems.
What=s available?
While a number of products come to mind, the one used most widely is
glyphosate (Roundup Ultra Max, Touchdown, and others). It=s safe, easy to handle and allows you to plant soon after application.
Pre-Harvest -
Corn
If making applications to corn as a harvest aid, there are
precautions. For corn, the label for
both Roundup Ultra Max and Touchdown state, AApply at 35 % grain moisture or less. Ensure that maximum kernel fill is complete
and the corn is mature (black layer formed).
Allow at least 7 days between application and harvest."
Rates:
Roundup Ultra Max - Apply up to 2.4 quarts/acre by ground and
26 ounces/acre by air
Touchdown - Apply up to 3.0 quarts/acre by ground and up to 1.0 quart/acre by
air
For Roundup-Ready corn, though, the maximum amount used
pre-harvest is 26 ounces/acre for Roundup Ultra Max and 1 quart/acre for
Touchdown. Allow at least 7 days before
harvest. Also, allow 50 days between
application of these materials and harvest of corn for forage.
Pre-Harvest -
Soybeans
For soybeans the labels for Roundup Ultra Max and Touchdown
are similar. Roundup Ultra Max or
Touchdown may be applied pre-harvest as a broadcast spray with ground or aerial
equipment. Apply to mature soybeans
when pods have lost their color. Make
pre-harvest applications at least 7 days before harvest with no more than 4.8
quarts/acre by ground (Roundup Ultra Max) or 6.0 quarts/acre for Touchdown; nor
more than 26 ounces/acre by air (Roundup Ultra Max) or 1 quart/acre for
Touchdown. Allow 7 days between
application and harvest. Allow at least
25 days before grazing or harvesting for livestock feed following harvest aid
application.
For Roundup-Ready soybeans, the pre-harvest application has to
be made at least 14 days before harvest with no more than 26 ounces/acre of
Roundup Ultra Max or 1 quart/acre of Touchdown. Do not graze or harvest for forage or hay
Gramoxone Max is
also labeled as a harvest aid for soybeans. The rates run from 5.5 to 11.0 ounces
per acre. For indeterminant varieties
apply when at least 65% of the seed pods have reached a mature brown color or
when seed moisture is 30% or less. For
determinant varieties, apply when plants are mature, i.e., beans are fully
developed, 2 of the leaves have dropped, and remaining
leaves are yellowing. Do not apply
within 15 days of harvest. Do not graze
or harvest for forage or hay.
Post-Harvest Fall
Weed Control
Roundup Ultra Max
and Touchdown are the two most widely used herbicides for Fall weed
control. You don=t have the residual activity that 2,4-D or
Banvel have when considering a Fall planting of small grains. In general, you should wait at least 7 days
after a glyphosate application before tilling or mowing.
Rates - In general, I recommend a minimum of 1.5 quarts/acre of
Touchdown (38 ounces per acre or Roundup Ultra Max). If you can go up to 2.0 quarts/acre of
Touchdown or 52 ounces per acre of Roundup Ultra Max, you may see a somewhat
better control of perennials when examining regrowth the following year.
2,4-D or Banvel
can be used alone or tank-mixed with the glyphosate-type materials. However, I still recommend that you use
at least 1.5 quarts/acre or either product (based upon a 4.0 lb ai/gallon
material). You can mix and match. For instance, you could use 1 quart/acre of
Touchdown (26 ounces/acre of Roundup Ultra Max) and add 1 pint of 2,4-D or
Banvel. However, 2,4-D and Banvel do
provide some residual activity. In the
case of 2,4-D, fall seeded small grains are restricted to the following
year. For Banvel, fall seeded small
grains are restricted to 30 days after application per pint of Banvel
used.
One other product labeled for post-harvest weed control is Harmony
Extra. This product has very good
activity on dock, wild garlic, and numerous winter annual broadleaf weeds that
may be emerged at time of application. Use
rate is 0.5 to 0.6 ounces/acre.
Wheat, barley and oat may be planted anytime after a Harmony Extra
application. Do not exceed 1.0
ounces/acre per crop season. Harmony
GT is labeled in a similar fashion but does not have as wide a spectrum of
control as Harmony Extra has.
Small Grain Weed
Control
There appears to be an interest in planting small grains under
minimum-till or no-till conditions.
While this may not be the best route to go with disease concerns, small
grains will continue to be planted in this fashion.
A good knock-down treatment will be necessary where emerged vegetation
exists. Roundup Ultra Max, Touchdown
and Gramoxone Max are the 3 products most widely used for knock-down
control of existing vegetation. For
Roundup Ultra Max, 19 to 26 ounces/acre, or for Touchdown, 1.5 to 2.0 pints/acre
should control most small emerged vegetation.
For Gramoxone Max, use 0.75 to 1.75 pints/acre.
In-Crop Weed
Control - Broadleaf Weeds
Harmony Extra has
the lion=s share of the market where broadleaf weed
control in small grains is needed. For wheat
and barley, applications can be made after the crop is in the 2-leaf stage,
but before the flag leaf is visible.
For Spring oat, make applications after the crop is in the 3-leaf
stage, but before jointing.
For barley and wheat, apply 0.3 to 0.6 ounce/acre. Do
not exceed 1.0 ounce/acre per crop season.
For heavy weed pressure, especially where wild garlic is present,
consider 0.5 to 0.6 ounces/acre. Best
activity on wild garlic will occur when plants are less than 12 inches
tall with 2 ro 4 inches of new growth.
Plants hardened-off by cold weather and/or drought stress may be more
difficult to control. Thorough spray
coverage of all garlic plants is essential.
Harmony Extra has activity on Canada thistle. Use 0.6 ounce/acre when all thistles are 4
to 8 inches tall with 2 to 6 inches of new growth.
For Spring oats, Harmony Extra applications are limited to 0.3 to 0.4
ounce/acre. Do not make more
than one application of Harmony Extra per crop season on oat.
Harmony GT is also
available and is actually one of the components in Harmony Extra. Rates and timings are the same as Harmony
Extra. While good on common chickweed
and garlic, Harmony GT is weak on henbit and will not control Canada
thistle.
For both herbicides, do not graze or feed forage or hay from treated
areas to livestock. However, the
harvested straw may be used for bedding and/or feed.
Grass Control
With the wide spread use of Harmony Extra, we are seeing more
grassy-type weeds invade small grain fields.
The following lists the more common ones.
Grasses Invading Small Grain Fields
- Annual bluegrass
- Bromegrass species
- Bulbous oatgrass
- Italian ryegrass
- Roughstalk bluegrass
Axiom (by Bayer) was
given a Section 18 (emergency use exemption) in Virginia for the 2000 - 2001
growing season for preemergence use in wheat for control of ryegrass. While they are renewing the Section 18 for
the 2001 - 2002 cropping season, they are now looking at a delayed application
of Axiom, after the wheat is out of the ground. We have been looking at Axiom and Dual II Magnum
(by Syngenta) for preemergence control of ryegrass in wheat over the past three
years. Both look very promising! The following two tables are averages for
1999 and 2000. We applied Axiom and
Dual II Magnum right after planting wheat in the Fall of 1998 and 1999. The data presented were observations made in
the Spring of the year. Our 2000 - 2001
data look similar.
Product Rate % Ryegrass
(lb ai/acre)
control
Axiom 0.213 74
0.319 94
0.425 94
0.532 99
Dual II Magnum 0.25 69
0.38 78
0.50 95
0.75 95
1.00 95
We have taken these plots to yield and have seen no injury nor yield
reduction with neither product.
One new herbicide that we=ve been looking at for control of grassy weeds in wheat is a product
from Monsanto called Maverick.
Maverick is labeled for control of a variety of bromegrass species
including downy brome, cheat and hairy chess which are
common in our region. We have studied
its use on annual bluegrass, roughstalk bluegrass and bulbous
oatgrass, and have found excellent control of annual and roughstalk
bluegrass.
Bulbous oatgrass
control has varied, but Maverick is the only product that we have found that
has any activity on this particular grass.
Use rate is 2/3 ounce/acre plus surfactant.
Maverick is labeled preemergence, Fall postemergence and Spring
postemergence. Consult the label for
the proper application timing for your specific needs.
Maverick is a sulfonylurea and safety to double-crop soybeans is a
concern. The current Maverick label
says, ADo not plant to any crops other than winter
or spring wheat for a period of one year following Maverick herbicide application.@ We
have two year=s data which shows that a planting of STS
soybeans, even where Maverick was spring applied, will not show any signs of
injury or yield reduction. Recently,
the label was amended to allow for a planting of STS soybeans where Maverick
has been used.
Odds and Ends
We=re currently updating our Pesticide
Recommendation Guide (EB 237).
We=re going to make a number of changes that
should help you and your clientele. It
should be ready for distribution by the end of the year.
The 6th annual Mid-Atlantic Crop Management School is
scheduled for November 13 - 15, 2001 at the Princess Royale Hotel and
Conference Center in Ocean City, MD.
While the school is geared towards Certified Crop Advisors gaining their
continuing education units, it is open to anyone. Enrollment is limited to 200 people. For information contact Dr. Richard Taylor at the University
of Delaware (302-831-1383).
That=s it for now. Will be getting out one more edition before the end of the year
covering the changes in Extension Bulletin 237.
Ronald L. Ritter
Extension Weed
Control Specialist