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Bruce Burdick
1109 S. Birch St.
Albany, MO 64402
660-726-5610
Email:
BurdickB@missouri.edu
Hundley-Whaley Center phone
660-726-3698
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February, 1999
Enhancing Select plus Cobra Tank Mixes
by Donald E. Null, Regional Agronomy Specialist
University Outreach and Extension, NW Region
Situation: Select plus Cobra tank mixes generally
provide excellent control of annual grasses and common waterhemp in
soybeans. Cobra alone provides fair to good control of large seeded
broadleaf weeds but that is too low for producers with heavy pressure
of cocklebur and sunflower.
Objective: Determine products that will enhance Select
plus Cobra tank mixes.
Methods: Soybeans were planted on May 27 into an area
with very heavy giant foxtail, common waterhemp and cocklebur
pressure. Late post herbicide treatments were applied on June 30 to
plots with V4 soybeans, 4-12" giant foxtail, 3-14" common waterhemp
and 4-16" cocklebur.
The rates of application for products were Select 2EC, 6 oz/acre;
Cobra 2EC, 6 oz/acre; FirstRate 84WP, 0.3 oz/acre; and Expert 75WG,
1.5 oz/acre. All tank mixes included 1 pint/acre of crop oil
concentrate and 2.5 pounds/acre of ammonium sulfate.
Results: Treated plots were rated July 15, two weeks
after the post treatments were applied. The effects can be seen in
the graph below. Both FirstRate and Expert improved the level of
cocklebur control to either complete or near complete control.
However, the tank-mix that included Expert tended to antagonize the
weedy grass control provided by Select. Increasing the rate of
Select to 8 ounces/acre did enhance the grass control to 90% but
that would still not be an acceptable level of control for many
producers. FirstRate did not antagonize Select.
Leaf area reduction, due to leaf burn (necrosis), was estimated one
week following herbicide application. Select + Cobra and Select +
Cobra + Expert tank mixes reduced soybean leaf area by 20-22%. The
Select +Cobra + FirstRate tank mix reduced leaf area by 15% which
was significantly less than the two other tank-mixes. Select +
FirstRate and Select + Expert treatments did not reduce soybean leaf
area. These two tank mixes provided no control of the ALS resistant
waterhemp at Hundley-Whaley.
Figure 14 Study 2620
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