Influence of Tillage, Rotations, and
Herbicides
on Perennial Weed Management
Beverly
R. Durgan
Minnesota Extension Service Weed
Scientist
HTML Editors: Jochum
Wiersma & Tracy
Allrich
A perennial weed is a plant capable of
surviving for three or more years. Perennial weeds
can spread by vegetative reproduction
(rhizomes, stolons, and tubers) and
seed production.
Methods of perennial weed
management fall into three categories: (a)cultural - such as crop rotations,
(b) mechanical - such as tillage with a plow, disk
or cultivator, and (c) chemical - with herbicides.
Effective management of perennial weeds
requires a combination of all these methods.
It is difficult to eradicate
perennial weeds from a field
when using only one method of control. In
fact, it may be impossible to completely eradicate
perennial weeds from a particular field.
The goal of a perennial weed management system
should be to keep perennial weed
populations below economic levels and prevent
spread within a field
and to other fields.
Perennial weed populations are influenced
by many factors. These factors include:
tillage, crop rotations, and herbicide
application and timing. In recent years, soil
conservation programs have resulted in the decreased
use of the moldboard
plow and increased
use of reduced
and no-tillage systems. Recent research has
shown that perennial weed populations increase
in reduced and
no-till cropping systems (2, 3, 6, 7, 8, 9, 10, 11). Fry and
Durgan (4, 5) found that common milkweed
population increased faster in a no-till
soybean, corn and small grains system than in
a conventional (moldboard)
corn soybean, and small grain system.
Perennial weed populations are also
influenced by crop rotations. Some perennial
weeds, such as common milkweed,
are easier to control when small grains are in the rotation system (2, 3).
Other crops, such as alfalfa, help control the establishment and
spread of many perennial weeds,
such as Canada thistle and
common milkweed (6, 8, 9, 10).
Herbicide application and
timing can also play an important role in the establishment and
spread of perennial weeds.
Fall herbicide applications can provide
some of the best perennial weed control of the
season. However, it is important to realize that herbicides
alone, or one herbicide application will
generally not eradicate a perennial weed
population. It will generally take more than one herbicide
application, and the combination of tillage and
crop rotation for good perennial weed
control.
Although, fall herbicide application provide
the best control of perennial weeds, they do
not always provide acceptable perennial weed
control. Many factors influence control including:
- Good
active growth of the perennial weed as
needed.
New shoots should be from underground
parts (rhizomes); leaves on old stems
(one that flowered that year) are less
effectively treated. It is best to have 6
inches of new regrowth before herbicides
are applied. Applying herbicides
to perennial weed regrowth after small
grain harvest is a good option. If
perennial weed regrowth does
not occur, it would be best (more
economical) to forget a herbicide
treatment this fall, and wait to control
the perennial weed the following year.
- Perennial weed
plant growth should not be drought
stressed or frost damaged.
Wait at least 24 hours after temperatures are below 26 - 28 degrees
F to evaluate foliage. Try to apply herbicides
when expected high temperatures will
exceed 60 - 65 degrees
F during the day
of application. Research has shown that herbicide
effectiveness decreases dramatically
after temperatures drop to the mid
to low 20's.
- Select the best herbicide
for the situation and crop rotation. Use
the highest labeled rate possible.
However, many herbicides have strict
rotation restrictions when applied in the
fall. Read the information in the
"Cultural and Chemical Weed
Control Bulletin" (1) under the
perennial weed control section and
read and
follow the restrictions on the label.
- Perennial weed
control will be greatest if the field has
not been tilled prior to herbicide
application. Mowing perennial weeds
earlier in the season as a good
"set-up" for fall control.
- Perennial weed
control is enhanced by tillage after a
herbicide application. Plan to till 2 to
4 weeks after herbicide application. Late
fall tillage at least 2 weeks after spraying often adds
10 to 30 % control.
- Plan a crop, tillage and
herbicide program for next year that
keeps pressure on the perennial weed.
Alfalfa and small grains are a better
follow-up choice that corn or soybeans.
- One herbicide
application will generally not give complete control. Additional
spot - treatments maybe needed
in the spring.
Herbicide choice, rate and
time of application are important factors for treating perennial weeds
in the fall. The following is a discussion on
some of the options for fall perennial weed
control. This is not a complete list, and you
should always refer to and
follow the herbicide label for rates,
application times and recropping restrictions.
The Minnesota Extension Service Bulletin "Cultural an Chemical Weed
Control in Field Crops - 1995" also has
an extensive discussion on perennial weed
management and can be used
as a reference (1).
Roundup
(glyphosate): Roundup can give
effective control of many perennial weeds,
including Canada
thistle, quackgrass and common milkweed,
when applied in the fall. Application rates depend
on the species, however, in all causes there must be adequate
regrowth of the weed for foliar uptake, as
Roundup has no soil residual.
The rates for fall applications are
as follows:
Quackgrass:
Apply 1 to 2 qts/A when quackgrass
is 6 to 8 inches tall and actively growing.
For the 1 qt/A rate apply 0.5 to 1% v/v nonionic surfactant in 3 to 10 gpa of
water. DO NOT till between harvest and fall
applications. Allow 3 or more days after
application before tillage.
Canada
Thistle:
Apply 2 to 3 qt/A after harvest
allowing at least 4 weeks for initiation of active growth and
rosette development. Allow 3 or more days
after application before tillage.
For suppression of Canada thistle, apply at 1
qt/A plus 0.5 to 1% v/v of nonionic surfactant in 3 to 10 gpa water. Roundup
at 1 pt/A can also be tank mixed with 2, 4-D
at 0.5 .lb./A (1 pt/A of a 4 lb./gal formulation) plus 0.5 to 1% v/v of
nonionic surfactant in 3 too 10 gpa of water. Allow 3 or more days
after application before tillage.
Milkweed:
Apply 3 pt/A of Roundup
to actively growing common milkweed plants.
Allow 7 or more days after application before
tillage. Do Not apply Roundup to common
milkweed after harvest unless there is adequate
regrowth as the Roundup will not give
effective control.
Roundup can also be tank mixed
with Banvel (dicamba) or 2,4-D for increased
control. When tank mixing Roundup with Banvel
or 2, 4-D the Roundup rate can be reduced.
Roundup can also be applied
as a "spot-treatment" to patches of perennial weeds.
For best control, use a 2% solution (2 qts Roundup
per 25 gallons of water).
Recropping Restrictions:
Roundup
has no soil residual,, and
therefore no recropping restrictions following fall applications.
Banvel (dicamba):
Banvel can give effective control
of many perennial broadleaf weeds,
including Canada
thistle and common milkweed,
when applied in the fall. Application rates depend
on the species, however, in all cases there must be adequate
regrowth on the weed. Banvel has soil residual,
therefore follow crop selection is important.
The rates for fall
applications are as follows:
Canada
Thistle:
Banvel can be applied
an 0.5 to 2 lb./A (1 to 4 pt/A) after harvest to actively growing Canada
thistle. Allow 7 or more days after
application before tillage. Banvel can also be tank mixed
with 2, 4-D or Roundup. This will allow the
use of lower Banvel rates (1 to 2 pts/A) in order
to decrease carryover potential.
Milkweed:
Banvel can be applied
at 0.5 to 2 lb./A(1 to 4 pt/A) after harvest to actively common milkweed.
Allow 7 or more days after application before
tillage. Banvel can also be tank mixed with 2,
4-D or Roundup. This will allow the use of
lower Banvel rates (1 to 2 pts/A) in order to decrease
carryover potential.
Recropping
Instructions:
Banvel has soil activity and
recropping restrictions following fall applications. Corn, sorghum, and
wheat may be planted in the spring following
fall applications. However, for all crops, injury may occur if the interval
between Banvel application and planting is
less than 45 days per pint (0.5 lb./A) used,
excluding days
when the ground is frozen. Research at North
Dakota State University indicated
that visible injury to wheat and barley planted
the following spring, but the effect on yield
was minimal. Banvel at 1 pt/A (0.5 lb./A) applied
in late September prevented seed
production of sunflower planted
the following spring.
The approximate ranking of crops from most to least
tolerant of Banvel residues is:
·
Corn
·
wheat
·
barley
·
oat
·
potato
·
buckwheat
·
soybean
·
drybeans
·
sunflower
·
flax
·
sugarbeet
Therefore, if Banvel is applied
in the fall at 1 pt/A or more in the fall, the "safest" crops to
plant the following spring are: corn, wheat, barley, oats, or other grasses.
There will be a risk of crop injury to soybean.
Curtail and
Stinger:
Curtail and
Stinger both contain the active ingredient,
clopyralid, which is very effective for
control of Canada thistle. Curtail is a premix
of clopyralid and
2, 4-D amine. Curtail and Stinger both have
soil residual, therefore follow-crop selection
is important.
Curtail:
Apply Curtail at 2 pts/A to
actively growing Canada thistle. Allow 14
weeks following application before tillage.
Stinger:
Apply Stinger at 1/4 to 2/3 pts/A
to actively growing Canada Thistle. Extreme
growing conditions (such as drought
or near freezing temperatures) prior to, at, and
following application may reduce Canada
thistle control. Allow 14 to 20 days following
application before tillage.
Recropping Restrictions:
Curtail and
Stinger have soil activity and recropping restrictions
following fall applications.
Curtail:
·
Do Not plant wheat, barley, oats, grasses, and
corn within 0 days after an application of
Curtail.
·
Do Not plant sugarbeets in the same growing
season following an application of Curtail.
·
Do not plant alfalfa, sweet corn, or canola for
10.5 months following an application of Curtail.
·
Do Not plant drybeans,
soybeans, and sunflowers for 10.5 months after
an application of Curtail, or 18 months if soil contains less than 2% organic
matter and precipitation is less than 15
inches during the 12 months following
application.
Therefore, when Curtail is applied
in the fall, ONLY wheat, barley, oats, grasses, corn or sugarbeets should
be planted the following spring.
Stinger:
Wheat, barley, oats, grasses, field
corn, and sugarbeets may be planted
anytime following application.
·
Do not plant alfalfa, sweet corn, or canola for
10.5 months following an application of Stinger.
·
Do Not plant soybeans, soybeans, and
sunflowers for 10.5 months after an application of Stinger, or 18 months if
soil contains less than 2% organic matter and
precipitation is less than 15 inches during
the 12 months following application.
Therefore, when Stinger is applied
in the fall, ONLY wheat, barley, oats, grasses, corn or sugarbeets should
be planted the following spring.
2,4-D:
2,4-d
can be applied in the fall for the suppression
of many broadleaf perennial weeds.
As mentioned earlier, 2,4-D is most effective
when used in combination with other herbicides
such as, Roundup, Banvel and
clopyralid. 2,4-D use rate in the following
fall is 0.5 to 2 qts/A (4 lb./gal formulation). Ester formulations generally
give better control than amine formulations. When 2,4-D is applied
in the late fall, at the high use rates, there is a possibility of carryover.
Crop injury may occur to broadleaf crops such
as soybeans and sunflowers.
Finally, remember that perennial weeds are difficult
to control. One herbicide application will not
give complete control. A two to three year control program is generally needed
to achieve complete control of perennial weeds.
However, for some perennial weeds, such as
milkweed, complete eradication
from field may not be possible. Therefore the
goal should be to decrease
perennial weed populations in order
to prevent sever crop yield losses and
prevent continued spread
of the weed throughout the field.
Literature Cited
1. Durgan, Beverly, R., J. L. Gunsolus, and
R. L. Becker. 1994. Cultural and Chemical Weed
Control in Field Crops. BU-3157-S. Minnesota
Extension Service. University of Minnesota
2. Fry, T. A., B. R. Durgan, and
D.L. Wyse. 1990. Common milkweed control in
spring wheat. Proc. North Central Weed Control
Conf. 43:10
3. Fry, T. A., B. R. Durgan, and
D.L. Wyse. 1990. Common milkweed seedling
establishment in spring wheat. Proc. North Central Weed
Control Conf. 43:121
4. Fry, T. A., B. R. Durgan, and
D.L. Wyse. 1991. Common milkweed seedling
establishment. Proc. North Central Weed
Control Conf. 46:110-111.
5. Fry, T. A., B. R. Durgan, and
D.L. Wyse. 1992. The effects of tillage practices on the vertical distribution
of simulated weed
seed and its
relation to common milkweed seedling
establishment. Proc. North Central Weed
Control Conf. 47:133.
6. Doll, Jerry D. 1992. Controlling Canada
Thistle. North Central Regional Extension Publication No. 218.
7. Doll, Jerry D. 1993. Quackgrass management in
field crops. North Central Regional Extension
Publication No. 219.
8. Salzman, F., KW. Renner, and
J. Kells. 1992. Controlling Canada Thistle.
IPM Extension Bulletin E-2245. Michigan State University.
9. Salzman, F., KW. Renner, and
J. Kells. 1992. Controlling Common Milkweed.
IPM Extension Bulletin E-2246. Michigan State University
10. Salzman, F., KW. Renner, and
J. Kells. 1992. Controlling Common Hemp Dogbane. IPM Extension Bulletin E-2247.
Michigan State University.
11. Salzman, F., KW. Renner, and
J. Kells. 1992. Controlling Quackgrass. IPM Extension Bulletin E-2251. Michigan
State University.
Minnesota Association of Wheat Growers
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