Page 4 - June 2017 Quarterly Newsletter
P. 4
AGRICULTURE & NATURAL RESOURCES MICHELLE BUCHANAN
Controlling Larger Weeds in Roundup Ready
Soybean Fields
Controlling annual weeds postemergence in Velvetleaf
Roundup Ready soybeans is always easier when the Velvetleaf has sometimes been difficult to control
weeds are small – less than 2 inches tall is with glyphosate. There are no confirmed cases of
preferable for good control. Once weeds get taller, glyphosate-resistant velvetleaf, but it is not
they are often considerably more difficult to extremely susceptible to glyphosate. Several
control. However, conditions are not always application factors can affect control, including
conducive to getting optimal postemergence weed time of day, hard water, ammonium sulfate, and
control. The following are some suggestions for environmental conditions. Velvetleaf control with
controlling larger troublesome weeds in soybeans. glyphosate can be optimized by using full rates of
glyphosate and ammonium sulfate (17 lb/100 gal of
Marestail spray), spraying during the daylight hours, and
Fall and early burndown treatments are critical to spraying when the plants are under minimal
the long-term management of marestail. drought stress. Herbicide tank-mix partners with
Unfortunately, that doesn’t always happen. The glyphosate that may enhance velvetleaf control
most effective herbicide treatment for controlling would include Resource, Cadet, Marvel, FirstRate,
marestail post-emergence in Roundup Ready Harmony, and Synchrony.
soybeans is probably a tank-mix of glyphosate plus
FirstRate. The combination of the two herbicides Sunflower and Cocklebur
seems to work better than either herbicide alone, Fortunately, sunflowers and cocklebur are still
even on resistant plants. Other tank-mixes to quite susceptible to glyphosate. However, these
consider with glyphosate for controlling marestail weeds are fast growing and often have multiple
would include Classic and Synchrony herbicides. flushes of germination. It is important to use the
Liberty 280 herbicide has provided fairly good full rate of glyphosate and get good spray coverage
control of large marestail as a burndown treatment when trying to control larger sunflower and
or postemergence in Liberty Link soybeans. cocklebur. Tank-mixing Scepter or Classic
herbicide with glyphosate may improve control and
Waterhemp and Palmer amaranth help provide residual control of later-emerging
Glyphosate-resistant waterhemp and Palmer plants.
amaranth are common in Kansas. The best way to
manage these pigweeds in soybeans is to use Conclusion
effective preemergence herbicides followed by If weeds have gotten large, it’s always best to start
postemergence treatment. However, sometimes the with the highest labeled rate of glyphosate, with the
preemergence herbicides weren’t applied or didn’t proper adjuvants, and add other herbicides as
get activated in a timely manner. Flexstar, Cobra, needed, depending on the weed species present. In
Marvel, and Ultra Blazer can be fairly effective for most fields, there will be a combination of one or
controlling small pigweed, but are less effective as more of the weeds listed above, so producers will
the pigweed gets larger. These herbicides also have to see how the herbicide options match up and
provide some residual weed control, so tank-mixes select the best combination.
of these herbicides with glyphsosate should be
applied within 3 to 4 weeks after planting to
optimize performance.
