Posted: July 7, 2009

More work needed to confirm possible resistant giant ragweed in a soybean field near Windsor.

Given the popularity and importance of glyphosate in today's farming systems, the potential for glyphosate resistance has been a nagging concern. So when the University of Guelph reported two of its plant agriculture researchers are investigating a suspected but unconfirmed case of resistant giant ragweed in a soybean field near Windsor, Ont., it generated interest. (See the original University of Guelph story here).

The researchers are in early stages of investigating the situation and the university is working cooperatively with Monsanto on these research efforts. Additional greenhouse and field research experiments on this weed population are planned throughout 2009, and among this research will be studies to confirm the resistance to glyphosate and the management options for the grower involved.

Canada Sprayer Guide reached Monsanto spokesperson Trish Jordan for perspective from the company.

"A fairly detailed scientific and academic process needs to be completed before the weed in question can be considered to be resistant," she says. "Obviously, we take all potential cases seriously and will work with the academics to investigate this situation fully. We recognize how important a tool glyphosate has become for farmers."

Assessment first priority

Monsanto's starting point is helping determine management needs for the field concerned, says Jordan. The company is working with the grower and academics to confirm what glyphosate the grower used and what his rates and application history were. "This is all part of trying to determine what and how this happened and hopefully come up with management recommendations that will help the grower better manage this situation if it is found to be a case of resistance in his field."

Jordan points out there are currently no weeds that have found to be resistant to glyphosate in Canada. Fifteen other weed species – including giant ragweed – have previously been confirmed as glyphosate resistant in other world areas. In some suspected cases of resistance previously investigated in Canada, further research actually determined that the suspected weeds were in fact, not resistant.

Good field management

Dr. Mark Lawton, Monsanto Canada's technology development lead in Eastern Canada, reminds growers that starting with a clean field, applying glyphosate at the right rate and right time, and including other herbicides and cultural practices where appropriate are important in preventing glyphosate resistance.

Resistance evolves after a weed population has been subjected to intense selection pressure in the form of a repeated use of a single herbicides and without adequate incorporation of cultural weed management options, says Lawton. The herbicide controls all the susceptible weeds, leaving only those that have a resistant gene to reproduce.

While a confirmation of resistance would be a first for Canada, the effective use of Roundup agricultural herbicides and Roundup Ready crops has continued in areas where glyphosate resistance has occurred in the past, says Jordan. "When glyphosate resistant weed biotypes have been identified in the past, they have been effectively managed with other herbicides and / or cultural practices."

Posted: July 7, 2009

In complex times, there's a lot to be said for the benefits of keeping things simple.

Most applicators would agree having the right nozzles is one of the most important parts of getting a spraying job done right. Years ago it was an area ripe for innovation and many welcomed the blossoming of new options, but today there are simply more types of nozzles than many growers and applicators can make sense of.

"There are a lot of new nozzles marketed now and I find farmers are often confused," says Ed Thiessen, technical crop manager with Syngenta "It wasn't that many years ago that a flat fan nozzle was the only thing out there. The big question was, 'do you want a 60, 80, 110 or 120 degree nozzle?' Those days have changed."

The key to sorting the flood of new options is to think in broad categories, says Thiessen, who deals directly with producers and applicators across the prairies on a daily basis during spraying season.

"Keep it simple. I think applicators have to ask three questions. What's their main objective in choosing a nozzle? What water volume are they applying at? What spray pressure are they applying at?"

There are no right or wrong answers to the first question. It's simply a matter of priority. "For some, drift may be their top concern because they're close to a residential area or because of weather conditions. In that case, low-drift nozzles are the priority."

Water volume considerations can vary greatly among different areas. "If you deal with growers in Manitoba, they like to put lots of water on. Similarly with fungicides where good coverage of large plants is needed. Whereas if you're in southern Saskatchewan, water can be at a premium, so they want to go at low volumes. Those priorities impacts on what type of nozzle you may want to buy. Some are better than others at each type of volume."

Considerations are similar for spray pressure. "Some of the newer nozzles require fairly high pressure to work properly. But there's no sense going that route if you don't have a modern sprayer that's capable of maintaining that high pressure."

Pressure range is the key factor to focus on. "With the rate controllers many newer sprayers use these days, often you want nozzles that work consistently under a wide range of pressures."

"Ideally, the best outfitted sprayers have the capability to have two or three different nozzle types on a boom, and can switch rapidly from one to the other to get maximum performance regardless of what type of product they're putting on. However it's a different situation for many of the older sprayers."

The key is to flesh out what your priorities are and what limitations you may be dealing with, then talk to people you trust.

"There's getting to be a lot of hype about nozzles and farmers need to sort it out," says Thiessen. "Just remember it doesn't have to be complicated."