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Know Waterhemp's Weaknesses
Want to get a soybean field
free of waterhemp like the one in this picture?
Know its two weaknesses, says
Kevin Bradley, University of Missouri Extension weeds specialist. Bradley spoke
at this week’s AGMasters conference at the University of Illinois. They include
Waterhemp seeds live relatively short lives in the
soil. Although its 4- to 5-year life
span may seem long to you, it’s a short
life from a weed perspective, says Bradley.
points to an Iowa State University (ISU) study coordinated by Bob Hartzler, ISU
Extension weeds specialist. Hartzler
found that after four years, just 10% of the waterhemp seed in the soil
a catch, though. This survival rate assumes no additional waterhemp seed is added
to the soil. If you continue to add seed to the soil due to mature plants shedding
seed each year, all bets are off.
you combine nixing waterhemp seeding preemergence residual herbicides, multiple
herbicide modes of action, and cultural practices can curb waterhemp
“I’ve seen it work in the
real world,” says Bradley. He notes a grower he worked with near Kansas City initially
had waterhemp-infested fields so severe soybeans could not be seen.
“By the end of three years,
he implemented everything we talked about,” says Bradley. These included steps
like preemergence residual herbicides and multiple herbicide modes of action.
“We started by not letting
waterhemp produce seed. I go by there once every summer, and I cannot find
waterhemp on that farm.
“The ultimate objective must
be to reduce the soil seedbank,” he adds. “If you have no other choice, that
means rouging a field.”
2. Waterhemp seeds do not emerge from lower soil
depths. “When they are 6- to 8-inches
deep in the soil, they will not come up,” says Bradley.
One way to place waterhemp seed
at lower soil depths—and tread carefully on this one—is to moldboard plow the
Now, don’t do this on highly
erodible soils. Bear in mind if you do it on no-till soils, negative
consequences include shattering earthworm tunnels that aid water infiltration.
In nightmare situations where
waterhemp chokes your soybeans out and you’re up against a wall, though, it is
It takes a moldboard plow, as
vertical tillage tools do not till the soil deep enough, says Bradley.
Once you bury the seed, don’t
moldboard plow the field again. If you do, you simply spring the waterhemp seed
back to the soil surface where it can emerge, says Bradley.