Fall Weed Management Options
Jerry
Doll
It's time to assess the possible need to treat weeds this
fall. This is particularly important for fields that will be
no-till planted next spring. Let's look at three typical
scenarios. 1. Old hay fields. These often have a mix of
alfalfa, some forage grasses, dandelions, quackgrass and perhaps
white cockle and some winter annuals like shepherd's purse or
chickweed. A common practice is to apply a combination of
glyphosate plus 2,4-D ester or dicamba and this is certainly an
effective program to kill the existing vegetation. Be careful
that these fields are not treated too early as winter annuals
and dandelions still have several weeks to germinate and grow
sufficiently to survive winter. Where possible, wait until the
first frost before treating old hayfields. This ensures that few
if any weeds will appear from seed after that and some weeds are
actually more sensitive to herbicides after a frost. None of the
species mentioned above is frost sensitive so they will still be
actively translocating sugars (and any applied systemic
herbicides) to their underground organs. Try and make the
application during a period of relatively warm weather (highs in
the 60s would be ideal). Pay attention to the possibility that
the canopy of the taller vegetation in these fields might be
protecting small dandelion or shepherd's purse seedlings.
Increasing the spray volume to at least 20 gal/A in these
situations might be in order. 2.
Harvested soybean fields going to no-till corn. Both
dandelions and white cockle are sometimes present after soybean
harvest. Because they have rosettes of leaves, which are
minimally affected by soybean harvest and are not covered by as
much crop residue as if they were in a corn field, they can be
effectively treated if these fields are to be no-till planted to
corn next spring. if white cockle is the weed of concern,
dicamba (alone or in combination with glyphosate) is probably
the best choice (and for any other weeds in the Pink family such
as common or mouse-ear chickweed). For common dandelion, 2,4-D
ester should be sufficient. If quackgrass is present with the
cockle or dandelions, then a combination of glyphosate and
dicamba or 2,4-D could be used. Another option for dandelion
control in fields that will be planted to corn is a combination
of Basis and 2,4-D ester. This is a labeled treatment and gave
excellent dandelion control when applied in the fall of 2001 in
a trial at Arlington. 3. Harvested corn fields going to
no-till soybeans. Success in this situation is more difficult
for two reasons: the crop is harvested later than soybeans and
there is more crop residue to contend with. Nevertheless, given
that fall treatments are so much more effective on perennials
like dandelions and white cockle, it is worthwhile to consider a
fall application in fields with significant dandelion or cockle
pressure. Remember, these weeds don not have to be very large to
survive winter so even fields with small perennials (which says
they germinated late season, probably after the corn canopy
opened up) are candidates for treatment. For dandelions, 2,4-D
ester alone or dicamba should be considered. Ideally, you
should wait a week or two after harvesting soybeans or corn
before spraying so that the weeds can recover and hopefully will
have some new growth when treated. Not every fall is like the
one we had in 2001 so judge the treatment timing in light of the
predicted temperatures and rain events. And because the idea of
fall treatments after soybean or corn harvest is relatively new,
perhaps it is best to treat a portion of a field or two to see
if the results warrant more wide-scale use of this practice. October 2002 |
