Herbicide Options For Open Pollinated/Conventional Corn
Corn acres on the Prairies have been steadily increasing, in part due to reliable shorter-season varieties with yield potentials that are good.
EARLY Weed management is extremely important.
First off and most importantly please source your herbicides early as some will need to be ordered in.
Also please touch base with your local crop herbicide advisor as they may have some information that hasn’t been mentioned below.
A critical weed-free period in Western Canada is important from first corn emergence to the eight leaf stage.
After this stage of growth the corn will be nearly ready to canopy and competition from weeds has minimal effect on the corn.
Corn is a relatively non-competitive crop in the early stages.
This is in part due to corn’s dislike of a crowd, be it weeds or other corn plants.
Researchers from the University of Guelph have shown that corn alters its growth pattern based on light waves reflected off neighbouring plants.
Dense or weedy corn stands negatively impact corn leaf architecture, decreasing photosynthetic efficiency and increasing the potential for yield loss.
Fortunately, weed populations are controllable. In Western Canada, weed management should be centred around a two-pass herbicide program that combines pre- and post-emergent herbicide applications and multiple modes of action. Depending on the herbicide and application rate, many of these herbicides provide residual weed control.
THE TWO PASS SYSTEM IS AS FOLLOWS:
The pre-emergent herbicides such as Frontier Max, Dual II Magnum, Prime Extra Light, or Atrazine and others which all have residual activity over 21 days are mainly grassy herbicides.
Followed if needed with a post emergent such as Armezon or Impact
and these two need a small amount of
Atrazine/ATTREX with them to be more effective —- they control both grasses and broadleaf and have residual as well for about 15 days.
Or a Dicamba product (Extendamax) and Pardner which do not have a residual but are excellent herbicide choices for broadleaf weeds.
This two-pass system maintains weed control for the duration of the CRITICAL WEED FREE PERIOD while managing the risk of herbicide resistance and existing resistant weeds —Because you are implementing the use of different groups of herbicides.
Pre-Emergent Corn Herbicides
Pre-emergent herbicides typically require one-quarter to three-quarters of an inch in rainfall after application to become activated (actual amount varies by herbicide).
However, excessive rainfall shortly after application can wash certain herbicides from the application zone, reducing efficacy and increasing the risk of crop injury.
If there are no signs of rainfall and the spring is dry harrowing the herbicide into the soil is required to incorporate and encourage activation of the herbicide.
The herbicide should be applied within 3 days of planting and immediately harrowed for best results.
Post-Emergent Corn Herbicides
The Group 4 herbicides 2,4-D, Buctril -M and MCPA, applied at two leaf stage also caused injury to the corn, a known side-effect of late application timing and/or sensitivity. Although the corn leaves outgrew their symptoms, weakened roots caused lodging and snapping later in the growing season.
Group 2 herbicides Option (Manitoba only) Accent, Ultim or Sortan IS and the Group 27 herbicide Armezon (Impact), were the best post-emergent choices, providing excellent grassy and broadleaf weed control.
Herbicides To Avoid
1. Buctril – M
2. MCPA
Recommendation
Weed management in corn is critical in the early stages of corn development to enable the corn to capture all the necessary moisture and nutrients it requires especially during drought situations.
The right strategy that needs to be implemented depends upon the weed species and the environmental conditions.
The information that we have provided in this document is only a guide to be used with caution as we cannot guarantee success and are only trying to provide information. Thanks
CATT CORN 1-204-723-2831.