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Are We Seeding Weeds?

Introduction of herbicide tolerant crops came with the promise of easier, cheaper and better weed control. Growers, especially those using zero tillage, now find that some of their worst weed problems are herbicide-tolerant volunteers from previous crops and/or plants growing from seeds the grower was unaware carried herbicide tolerant traits.

Martin Entz, professor with the University of Manitoba’s department of plant science, reports over 90 per cent of the Roundup Ready soybean fields he surveyed in Manitoba last summer had volunteer Roundup Ready canola. In most cases the soybeans were planted two or more years after the last crop of RR canola. In one field where RR volunteers were a problem, Entz found RR canola had not been planted for 10 years. Entz also discovered RR canola volunteers in RR corn. “As you add more Roundup Ready crops into a rotation, the problem with RR volunteers increases.”

In Alberta, the cold dry spring of 2009 opened the eyes of many growers to the extent of the problem of herbicide-resistant volunteers in crop. Large, green volunteer canola plants that survived the spring burn-off and herbicide applications or that germinated after the in-crop herbicide application were visible last summer in many ripening cereal fields. Unfortunately, if these volunteers carry the RR trait, glyphosate is ineffective for pre-harvest control and there are no other herbicides approved for that use in most crops.

Growers in this situation must either swath crops to dry down these volunteers or wait until late in fall for these volunteers to mature sufficiently so the crop can be straight cut.


Even more disturbing is the appearance of herbicide tolerant volunteers where these herbicide tolerant crops have never been grown. The accompanying photos show a field of Clearfield canola which was taken out of production with an application of 0.6 litres per acre of Roundup Transorb HC on June, 28, 2009. Roundup Ready canola had never been grown on this field or adjacent fields. This year, certified Clearfield seed had been planted and the air drill used for the seeding operation was new this spring. No Roundup Ready seed had ever been in the drill or tank

Inspection by both the seed sales rep and by two Monsanto reps confirmed that the green plants seen in the picture were Roundup Ready volunteers and the plants were unaffected by the glyphosate burn off. Both company reps also concluded the likely source of the RR contamination was in the seed as all the volunteers were in the seed rows. The Monsanto rep said it was likely these healthy canola plants carried both the IM and RR traits and these plants would have likely survived the application of a Clearfield product so this problem would never have come to light had the field not been taken out of production by the use of glyphosate alone. The rep said to always add 2,4-D to glyphosate when doing a burn off to control all types of canola.

The Monsanto rep suggested an application of 12 ounces per acre of 2,4-D would be needed to control the large volunteer RR plants. Given the 2004 Supreme Court of Canada ruling that confirmed Monsanto has patent protection and ownership of both the RR gene and the plants containing the gene, the grower asked if he would be compensated by Monsanto for the control of these volunteers since he never bought or planted RR canola on the field. He was told by the Monsanto rep that Monsanto was not responsible and he should seek compensation from the seed company.

While the seed trade has done a good job of convincing farmers to grow clean, pure seed, it is now debatable if the seed trade is able to provide such seed. While it is relatively easy to ensure seed is free of weeds, it is a much more difficult task to supply seed free of off types — especially if the only difference is the result of genetic modification.


Dale Adolphe, executive director of the Canadian Seed Growers Association (CSGA) stands behind the quality of certified seed. “Seed purity is assured by a combination of two things. First, all pedigree seed production must follow strict standards including previous land use, isolation distances between crops and field inspections. Second, a crop certificate is only granted after an accredited laboratory ensures purity and germination. A grower using certified seed has the right to ask the seed seller for the analysis of the seed; the seed tag enables the CSGA to trace back to the seed grower if there is a problem.”

With respect to herbicide tolerance, however, Adolphe admitted seed analysis only ensures the seed has the expected herbicide

Gerald Pilger took these two photos on July 28th, 2009. This field was seeded to Clearfield canola on May 10, 2009. This field had never had roundup ready canola on it and there was never RR canola planted adjacent to it. Due to drought and frost, the field was determined not to be viable. On June 25, AFSC estimated the potential yield at only 73 kg/acre. As a result, an application of 1 litre per acre of Roundup Transorb was made June 28, 2009 to kill surviving canola plants and weeds. The close-up photo (left) shows good kill of weeds and susceptible canola “so the application of glyphosate worked” however many canola plants which should not be Roundup Ready survived.

tolerance — it does not test for any other GM traits or if the seed has herbicide tolerance to more than one herbicide (trait stacking). “There are audits done of the system where some seed samples are actually grown out the following year to ensure our standards are meeting purity requirements and very few problems have been found.”

Adolphe says there are periodic reports of suspected seed contamination, but says most contamination happens after seed certification, rather than before. “There are a number of possibilities for contamination, such as in augers and seeding equipment. The field history and the efficiency of past herbicide applications must be assessed, too.

Adolphe’s assessment of the risk of seed contamination is at odds with that of Lyle Friesen, research associate with the University of Manitoba. “It is pretty well impossible to ensure seed is free of adventitious off types,” says. In 2002 Friesen et al completed a study of non Roundup Ready pedigreed canola looking for glyphosate herbicide resistance contamination. Fourteen of the 27 unique CSGA numbered samples of certified seed had contamination levels of more than 0.25 per cent and therefore failed the purity test for certified canola seed. Three of the pedigreed samples had contamination levels of more than two per cent.

These results were similar to those of Downie and Beckie, both of Agriculture and Agri-food Canada based at Saskatoon. A year earlier than Friesen’s work, they found 59 per cent of 70 certified seed lots had detectable levels of contamination, and 25 per cent of certified seed samples had contamination levels exceeding the maximum for certified seed status.

There are standards for allowable off-types in certified seed –a maximum 0.25 per cent by seed-lot. That percentage, you would think, would include the wrong GM trait, but it’s not being tested for. Friesen says that the problem — further amplified by the recent Triffid fiasco — is that there is no protocol in place to test at the breeder, multiplier and farm level, and two, no recourse should too many off types or misplaced GM traits be detected.

The problem of herbicide resistant seed purity is not limited to canola. In a 2004-05 study Todd Gaines, Colorado State University, looked at herbicide resistance contamination of conventional wheat seed with the imidazolinone resistance (IR) trait in eastern Colorado. In the 92 samples of both certified and farm saved seed tested they found IR contamination ranging from zero per cent to 11.28 per cent. One certified seed sample and three farm saved samples had more than 0.1 per cent IR contamination, the maximum allowable for seed certification.

Entz adds, “Nature does not work in a designated box. Nature does not contain a trait we put into plants to a certain field or area. The out crossing of herbicide tolerance in canola shows clearly that introduced traits cannot be contained. Before any new GM traits or crops, such as GM wheat, are introduced we need laws that will give the Canadian Food Inspection Agency the power to evaluate, segregate and regulate these new crops. And companies that introduce new GM crops and traits have to be held responsible and accountable if there is unintended spread of the trait in the environment.”

As well, the seed trade needs to review their current purity standards. Instead of just testing for traits that should be in the plant, tests must be done for traits that should not be present. These tests are already readily available and it is time they are required before seed is certified.

Ultimately, it is the grower who has the most to lose. Glyphosate is likely the most important herbicide ever developed and a must for successful zero tillage. As more RR crops are introduced and further RR contamination occurs these weeds could render glyphosate ineffective.

Will the costs of chemical cocktails needed for burn off actually increase rather than decrease farm herbicide costs? Will we lose the ability to zero till because we have lost the herbicide which made this practice possible? In a world increasing worried about food safety will our inability to police and contain introduced genetic traits cost us markets? Will it even be possible for organic producers to grow some crops given the widespread occurrences of herbicide resistant volunteers.

It is the grower, through choice of crops and a good herbicide rotation, who will determine the long-term viability of herbicides like Roundup and even the crops that can be grown. It starts with the quality and purity of the seed we use and controlling all volunteers from those seeds in the years following. That’s easier said than done.

Gerald Pilger farms at Ohaton, Alta.

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