Managing Roundup Ready Canola in Corn

Collaborators: Calvin Yoder - Alberta Agriculture & Forestry, Akim Omokanye - Peace Country Beef & Forage Association, Kim Schoorlemmer - DuPont Pioneer

From: Peace Country Beef & Forage Association 2016 Annual Report

Corn acreage in the Peace River Region for livestock feed has steadily increased over the past number of years. Most of the corn seeded is Roundup Ready (RR) which provides a good system for controlling weeds. Volunteer RR canola is also a common weed on fields where corn is grown. Managing volunteer RR canola in RR corn requires a broadleaved herbicide that can be mixed with glyphosate and be safely applied prior to seeding corn or applied in-crop.

Selecting a corn herbicide should be based on weeds present, crop stage, crop tolerance and price. There are a number of broadleaved herbicides that can be tank mixed with glyphosate and used on corn as pre-seed or in-crop applications. Tank mixing a broadleaved herbicide with glyphosate will improve control of a number of weeds including volunteer RR canola. Herbicides that can be tank mixed with glyphosate and applied prior to seeding corn are Heat, Pardner, Conquor, MCPA and 2,4-D. Some herbicides that are registered for use on corn and can be tank mixed with glyphosate include Pardner, Buctril M, 2,4-D, MCPA, Banvel and a new herbicide Armezon. Although Banvel, 2,4-D and MCPA are registered for use on corn, agronomists prefer not to recommend them as they can cause stunted growth and poor brace root development resulting in lower yields. Bromoxynil, which is the main active ingredient of Pardner, tends to be safer although can cause some leaf burn.

Methods

Trials were conducted in 2015 and 2016 to evaluate several herbicide tank mixes with Roundup WeatherMax to control volunteer RR canola and other weeds in field corn. One trial in 2015 compared several treatments applied prior to seeding (Table 1) and the second trial conducted in 2015 and 2016 compared treatments applied in-crop (Table 2). All treatments included in the trials are registered for use on corn.

Experimental design for the Pre-Seed Herbicide trial was a randomized complete block design with three replications and plots were 2m x 7m in size. Experimental design for the 2015 In-Crop Herbicide trial was a randomized complete block design with 2 replicates. Experimental design for the 2016 In-Crop Herbicide trial was a randomized complete block design with 4 replicates.

Herbicides were applied with a hand held plot sprayer, calibrated to deliver 100 l/ha of water at 270 kPa.

Pre-seed Herbicide Applications

The trial was conducted on a RR canola stubble field near Debolt. The site had uniform populations of volunteer RR canola. Herbicide treatments (Table 1) were applied on May 25th when the canola was at the 1-3 leaf stage. Corn was direct seeded into stubble through the trial area several days following the pre-seed herbicide applications. Visual weed control ratings (percent control) were conducted 22 and 35 days after application (DAA). No crop tolerance data was collected.

In-Crop Corn Herbicide Applications

This study was conducted in 2015 and 2016 on a field of RR corn along Alder Ridge Rd. that had been seeded to corn for a number of years but continued to have issues with volunteer RR canola. The trial area had uniform weed populations of volunteer RR canola, wild buckwheat and lamb’s-quarters and smart weed.

2015

Herbicide treatments (Table 2) were applied on June 17th when the corn was in the 5-6 leaf stage. Volunteer canola was in the 3-6 leaf stage, lamb’s-quarters 3-4 leaf stage and wild buckwheat at the 3-6 leaf stage. Visual weed control ratings (percent control) were conducted 26, 41 and 56 days after application (D-A-A). No crop tolerance data was collected.

2016

Herbicide treatments (Table 2) were applied on June 17th when the corn was in the 2-3 leaf stage. Volunteer RR canola was in the 2-3 leaf stage, lamb’s-quarters 3-4 leaf stage, wild buckwheat at the 1-4 leaf stage, hemp-nettle at the 1-3 leaf stage and smartweed at the 1-4 leaf stage. Visual weed control ratings (percent control) were conducted 16 and 28 days after application (D-A-A). No crop tolerance data was collected.

Results and Discussion

Pre-seed Herbicide Applications

Percent visual volunteer RR canola control following several pre-seed herbicide applications are shown on Table 3.

All pre-seed herbicide applications with the exception of Roundup WeatherMax provided excellent control of volunteer RR canola plants that were emerged at the time the herbicides were applied. Heat+Roundup Weath-erMax and MCPA ester+Roundup WeatherMax provided some residual control of volunteer canola that was germinating after the application. Pardner and Conquer tank-mixed with Roundup WeatherMax provided excellent control of emerged canola but did not provide any residual activity.

In-Crop Corn Herbicide Applications

Tables 4, 5 and 6 show control of volunteer RR canola, wild buckwheat and lamb’s -quarters following the application of several herbicide treatments applied in-crop on corn from the trial conducted in 2015.

Tables 7 and 8 show control of volunteer RR canola, wild buckwheat, lamb’s–quarters, hemp-nettle and smartweed following the application of several herbicide treatments applied in-crop on corn from the trial conducted in 2016

The addition of a broad-leaved herbicide to Roundup WeatherMax was needed to control volunteer RR canola. In most cases control of lamb’s-quarters, wild buckwheat and hemp-nettle was improved when a broad-leaved herbicide was tank-mixed with RU WeatherMax as compared to RU WeatherMax applied alone.

All broad-leaved herbicide tank-mixes with Roundup WeatherMax were effective at controlling RR canola, although the broadleaved herbicides MCPA ester, Armezon and Pardner appeared to provide more consistent control than the other products. Pardner and Buctril M treatments tank mixed with Roundup WeatherMax also provided more consistent control of wild-buckwheat than the other treatments. MCPA ester+Roundup WeatherMax provided slightly better control on all three weeds than MCPA amine+Roundup WeatherMax.

Summary

The addition of a broad-leaved herbicide to Roundup WeatherMax for in-crop herbicide applications on RR corn will improve control of most weeds particularly RR canola. Pardner, Armezon, Buctril M or MCPA ester tank-mixed with Roundup WeatherMax generally provided good control of all weeds sprayed in the study. It should be noted that herbicides containing MCPA, 2,4-D or dicamba are not generally recommended by agronomists for use on corn as they can cause damage to the corn crop.