Columbia, Missouri
April 1, 2008
Rising input costs have crop
farmers looking for price-competitive alternatives, said a
University of Missouri
(MU) weed scientist.
With a doubling in price for glyphosate, a post-emergence
herbicide that is most popular with soybean producers,
pre-emergence herbicides became price competitive, said Kevin
Bradley, MU Extension specialist.
“In the past, the cost of two applications of glyphosate on a
Roundup Ready soybean field has been unbeatable from an economic
standpoint,” Bradley said. “Now at chemical cost of $11 to $12
per acre for brand-name glyphosate treatment, many pre-emergence
soybean herbicides will cost about the same or less than
glyphosate.
“Although generic glyphosate products will likely remain
slightly lower in cost than many pre-emergence treatments, I
still think there is a strong case to be made for the use of
pre-emergence soybean herbicides.”
Pre-emergence herbicides control weeds before the seedlings come
up, preventing yield loss from early weed competition.
“Our survey of Missouri producers last year revealed that a
majority of first-pass glyphosate applications in soybeans were
made when weeds are 7 to 10 inches tall,” Bradley said. “At that
point, yield loss will probably have already occurred.”
“A pre-emergence herbicide will eliminate that early weed
competition and yield loss.” Although each weed species differs
in its competitive ability, Bradley recommends that glyphosate
be sprayed before the weeds in a field reach a height of 6
inches.
Bradley does recommend use of glyphosate for weeds that escape
or for weeds that emerge later in the growing season.
The advantage of glyphosate, now sold under the trade name of
Roundup PowerMax by Monsanto, is that it can be sprayed over the
top of Roundup Ready soybeans to kill weeds without harming the
beans. The ease of that treatment has made glyphosate the most
popular weed control method in soybeans.
“However, an advantage of pre-emergence herbicides is to rotate
herbicide modes of action and manage glyphosate-resistant weed
species. Repeated exposure to glyphosate, generation after
generation, has allowed herbicide-resistant weeds to develop.
“Surveys we conducted last year indicate glyphosate-resistant
waterhemp now occurs on 4 percent of the soybean acres in
Missouri,” Bradley said.
Pre-emergence herbicides available this year include Authority
First, Boundary, Canopy, Dual II Magnum, Envive, IntRRo, Prefix,
Prowl H2O, Sonic, Valor and Valor XLT. “All are currently
costing about the same or less than a brand-name glyphosate
treatment,” Bradley said.
Most of these also will provide good control of
glyphosate-resistant waterhemp. Continued use of glyphosate on
weeds showing resistance will only intensify the problem.
If producers decide to use glyphosate, they should not cut the
application rate to save costs. “Reduced rates usually translate
into reduced weed control and increased yield loss,” Bradley
said. “Cutting rates to save a few cents will likely lead to
lower yields at the end of the season.”
For years, soybean acreage has been the leading cash crop in the
state. |
|
