Soybean School West: Glyphosate Resistance Management with Roundup Ready Crops in Rotation

Volunteer Canola in Soy
Eyesore or yield robber? Depends on the volunteer canola density and your long term management goals.

Soybeans are a relatively new crop for many farmers in Western Canada. For many farmers, this brings a second RoundUp Ready crop (or possibly third) into rotation. Because of this, controlling volunteer canola ahead of the soybean crop is crucial, as high canola populations can have a significant yield impact, and more costly, as a glyphosate burn-off just isn’t going to cut it.

In the above Soybean School West audio episode (click here), Rob Gulden outlines the risks of volunteer canola in soybeans and the potential long-term impact of letting these towering plants set seed every year. From yield loss, to ongoing disease pressure for canola in rotation and more, Gulden also outlines the risk of glyphosate resistant weed biotypes as you add more RoundUp Ready crops in rotation.Soybean School West also spoke with Bruce Murray, with Monsanto Canada, to outline herbicide management options ahead of RoundUp Ready (RR) soybeans.

“There are number of good options to control RR volunteer canola ahead of RR soys, he says. “Monsanto has field tested two products, Heat and Valtera and observed good results. Both of these products are Group 14 products that have good efficacy on many weeds including volunteer canola.”

Heat and Valtera are Group 14 products they have a nice fit with regards to a sound herbicide rotation approach, Murray says. “Valtera  is a pre-seed soil applied product that is activated with precipitation. Do not apply this product after the soybeans and weeds have begun to emerge, however. If the volunteer canola is up Valtera will not control it.”

Heat is also a pre-emerge product but at the rates of application used ahead of soybeans the weeds must be up and growing, Murray says. “Heat will control a number of broadleaf weeds including volunteer canola up to the eight-leaf stage, however, not all weeds listed on the Heat label are controlled up to the eight-leaf stage so read the label for specifics.” Do not use the cereal or corn rate of application of heat prior to soybeans, he warns, as this higher rate will harm a soybean crop.

CleanStart is also an option, however must be applied much earlier, as it works best on seedling or two-leaf canola plants. “Tribenuron products, like Express SG, FirstStep, Nuance and Spike, also give excellent control of volunteer canola as a pre-seed application ahead of soy emergence,” Murray says.

“Tank mixing the above pre-emerge herbicides with pre-emerge Roundup applications is always a good idea,” Murray adds, in regards to preventing or delaying herbicide resistance. “It’s a great idea whether or not you’re growing RoundUp Ready canola, as there can be RR volunteers from other systems as well.”

Murray strongly encourages farmers to read and follow labels when decided on water volumes and considering re-cropping restrictions. “Each herbicide will be different. Contact herbicides, like one of the actives in CleanStart, for example, require higher water volumes to assure good coverage of the weeds.  Soil applied herbicides, like Valtera, also often require higher water volumes to assure good soil coverage. My best advice here is to read your labels and follow the directions on them.”

Tank-mixing different actives in a pre-seed burn-off is just one aspect of an integrated weed management plan, Murray says. A diverse crop rotation, starting with weed-free seed sources and cleaning equipment between fields is also important to decreasing the risk of weed seed movement between fields (it’s good for disease control too).  Scout your fields regularly and monitor the weed populations present and address any spray “misses” or escapes that you may notice in the field.

“There are a number of good post-emergence applications available to farmers wanting to grow more than one RoundUp Ready crop in their rotation,” Murray says. “Tank-mixing herbicides such a 2,4-D, Dicamba, Buctril M or Bromoxynil to RoundUp Ready Corn or Pursuit, Odyssey, Viper ADV, and Basagran to RoundUp Ready soybean Roundup applications are great options for delaying resistance.”

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