by Elizabeth A. Tomlin
Madison Co., a recent member of the Cornell Cooperative Extension’s Central NY Dairy and Field Crops group, hosted a Crop Congress featuring CNY CCE Field Crop Specialist Kevin Ganoe and CCE North Country Regional Ag Team Field Crops Specialist, Mike Hunter.
Hunter spoke to the group of producers assembled about herbicides, conventional weed control, Round-Up ready corn and resistance management.
“I know people don’t like to hear resistance management,” Hunter admitted. “But, we really need to pay attention to resistance management. When we talk about resistant weeds in New York State, soybean growers are dealing with resistant marestail and tall waterhemp now. These are going to be some issues and I know it’s going to be coming this way.”
Marestail/Canada Fleabane is a common weed throughout New York. However, once it becomes resistant, it changes the ball game.
“The known resistant populations have been identified in Cayuga County and west in the state. Our known resistant populations of marestail are able to survive applications to glyphosate (a.k.a. Roundup), a Group 9 herbicide. There is also strong evidence to show that we also have populations of marestail in Western New York that have multiple resistance and can survive applications of both glyphosate and Group 2 herbicides, such as Classic and FirstRate,” said Hunter.
Hunter explained producers using the same weed control for multiple seasons are contributing to the problem. “I’m going to challenge you, if this is happening on your farm, where you’re using the same weed control over and over again and getting good results, we might want to start thinking about can we change it up some.”
When do you dare to change it? You may wonder why you should change if you are getting good weed control.
“It’s a big decision you have to make,” remarked Hunter. “Maybe we should start switching up our sites of action we’re putting out there.”
Different tank mixes should be considered.
“We want to make sure we’re mixing it up enough so that these weeds don’t show up on our farms, because it makes it a lot more difficult,” said Hunter.
Hunter commented on how Round-Up Ready crops have made it easier for producers to grow successfully — especially producers of no-till crops.
However, he then showed photos of soybean fields that have been invaded by glyphosate resistant marestail.
“This is what some of this technology that we relied on has kind of led to,” he said. “Am I saying that Round-Up Ready Corn should not be used? Not at all. I’m all for the technology. I like it, it’s got a great fit. But, if we’re going to use it, we’re going to have to start mixing some things up with it now. And growers are going to have to do this.”
Hunter said most notable about marestail is that the seeds, with up to 200,000 seeds per plant and an 80 percent germination rate, are easily dispersed by wind.
“The seeds are attached to a featherlike structure, or pappus, similar to a dandelion. Research studies in the mid-Atlantic Region of the U.S. suggests that once the seeds get into the sky they can easily disperse more than 100 miles.” Hunter said it’s not a case of “if” resistant marestail will become a problem, but a matter of “when.”
“Why do we care? The yield loss there is huge,” he said. Loss of yield impacts income.
Hunter emphasized that grower observations are important in discovering these resistant weeds, since early unknown resistant weeds reproduce and spread quickly.
“We have those handfuls of weeds out in the field and nobody notices them,” said Hunter.
It takes about 30 percent of weed control failure before growers notice it. That failure is a lot and you may think you will pick up on it sooner, but that has not been the case.
Fields that didn’t get planted in 2017 because of extremely wet weather were a great place for resistant marestail to get a foothold.
So how do you manage for resistance?
Crop rotation is one method. Corn, soybean and wheat rotation is one suggestion.
Tillage works, too.
“Tillage is a really good method,” Hunter commented. “Marestail doesn’t like tillage.”
Next on the list is chemical tactics. Herbicide programs incorporating several different sites of action is key.
In tank mixes, different herbicides with different sites of action targeting the same weeds is essential.
“It complicates things a little more when we start coming up with these tank mixes. We want to have activity on the same weeds,” said Hunter.
Annual maps of Ontario, Canada showed how rapidly glyphosate resistant marestail will spread, invading crop fields — and was quickly joined by marestail with multiple resistances. Hunter pointed out that the distance to northern New York State is less than 30 miles.
Hunter said marestail also does not tolerate shading. “So, for the soybean growers, I challenge you, let’s see if we can get our soybeans planted earlier. Get a canopy closure as quick as you can.” Early May is not too early.
Tall waterhemp is another resistant weed becoming established.
“Tall waterhemp is one that’s in New York State,” reported Hunter. “It’s being found — and that’s going to be a nightmare to deal with.”
Tall waterhemp, characterized by rapid, early season growth, growing at more than one inch per day and quickly reaching over six feet, germinates throughout the growing season and has been found on farms in Central and Western New York. Fortunately, it’s not spread as easily as marestail.
The third weed Hunter described was Palmer amaranth.
The Weed Science Society of America ranks Palmer amaranth as the most difficult weed to control in the U.S. It has a devastating impact on crop yields. It is extremely prolific — a single Palmer amaranth plant may produce a million seeds per season — and has stems tough enough to damage farm equipment.
“There are no known populations of Palmer amaranth in New York but is a weed of concern that we need to be on the lookout for. That is one we don’t want to see,” said Hunter.
Ganoe spoke to attendees about looking at planting dates.
“Stop thinking about planting early or late,” Ganoe advised. “It isn’t a competition. Plant when you can and the risk is low.”
Ground temperature, soil conditions, compaction and growing degree days were discussed.
Ganoe said light harrowing may be necessary to break up crusting to promote best conditions for seedlings.
Planting in cooler conditions may be necessary if that is when your window of opportunity is open.
“Talk to your seed companies,” advised Ganoe. “Look for hybrids that perform better under some of these tough conditions.”
How deep are you planting your seed?
Although ideal depth is reported to be one and one-half inch deep, Ganoe said he would rather see corn planted two inches deep than not deep enough. This helps to avoid frost damage and also helps keep birds from destroying seedlings.
Attendees reported some damage to seedlings from crows and blackbirds.
“If you’re having problems with birds,” Ganoe advised, “Avipel is something that seems to work.”
Crop pests and disease were reviewed, including army worm, black cutworm, wire worm and slugs, which may be a problem in high residue situations, such as no-till.
For more information contact Ganoe at