Prevention is the best method when it comes to Roundup Ready canola volunteers in a crop of Roundup Ready corn.
If that fails there are pre-seed and in-crop herbicide options — but they’re risky, says Bruce Murray, a DEKALB agronomist with Monsanto.
“It you’re expecting a miracle, sorry there isn’t a miracle out there right now,” Murray told farmers at the recent Manitoba Special Crops Symposium.
Conventional canola volunteers are easy to control with glyphosate in Roundup Ready corn — but Roundup doesn’t kill Roundup Ready canola. Pre-seed herbicide treatments include: Clean Start (which needs to be applied when the canola is in the one- to two-leaf stage), bromoxynil plus MCPA and Heat.
Monsanto endorses Heat because it’s effective, has some residual control, belongs to Group 14, and is relatively affordable, Murray said.
“It works well and it works quickly.”
There’s also no antagonism when it’s mixed with Roundup and the tank mix can also be applied before seeding soybeans, he said.
In-crop options are 2,4-D, Basagran, dicamba plus 2,4-D, bromoxinal plus MCPA, and DyVel DSp. It’s safest to apply a 2,4-D-glyphosate tank mix when corn is in the two- to four-leaf stage, Murray said. When corn is in the four- to six-leaf stage mix glyphosate with bromoxynil plus MCPA.
“Do it earlier with the 2,4-D, do it on time with the Buctril-M (bromoxynil plus MCPA) and go fishing if you’re too late,” he said.
It’s risky spraying corn with phenoxy herbicides such as 2,4-D and MCPA, Murray stressed. The in-crop 2,4-D-glyphosate tank mix should be applied early when the corn is in the two- to four-leaf stage.
“It’s more an art than science,” Murray said. “If you get it wrong and get injury that first node (on the corn plant) gets brittle and if the wind picks up, it breaks off. That’s a real yield hit if you get it wrong.”
Corn that twists and flattens after being sprayed with 2,4-D or MCPA is unlikely to recover, he said.
Phenoxy herbicides are not recommended for use on corn in Ontario because the risk of crop damage is high. To minimize the risk, Manitoba farmers must apply the correct rate, at the right time, Murray said.
That means not spraying later than the six-leaf stage and holding off if the temperature and/or humidity are high, or if there are big differences between day and night temperatures.
Some corn hybrids are more susceptible to injury, so consult your seed dealer.
Preventing canola volunteers in the first place is best, but is easier said than done. Canola tends to be a weedier crop because it hasn’t been domesticated as long as some others, Murray said.
It shatters more easily at harvest and sometimes goes dormant. While dormancy can last four years, most canola seed germinates in the first season following harvest, he said. Research in Saskatchewan found some canola fields had 3,590 canola seeds per square metre on the ground after harvest — 20 times the normal seeding rate, he said. Shattering can be reduced by swathing canola when 25 to 30 per cent of the seed has changed colour, he said. Setting the combine to reduce losses helps, too.
Studies have shown it’s better to avoid tillage immediately after harvesting canola.
“(With) deep tilling, all you are doing is burying it and creating conditions where it is probably going to go dormant on you,” Murray said. “And then when you bring them back up, guess what happens?” They germinate and grow.
Often fall tillage isn’t needed because freezing temperatures in the fall will kill volunteer canola, he said.
“Sometimes fall tillage is not a bad thing as long as you wait long enough and let the canola germinate,” Murray said. “If you are tilling, don’t bury the stuff down six inches. You don’t need a lot to get rid of that canola — nice shallow tillage.”
Corn is a competitive crop later in the growing season, but it’s a wimp at the start. That’s why weeds should be controlled early, he said.
“If you don’t, it’s going to cost you and it’s going to cost you big time. It’s clear. If you wait you’ll lose yield.”