Roundup-Ready Wheat Position Paper

Saskatchewan Soil Conservation Association

Box 1360, Indian Head, SK S0G 2K0

306-695-4233

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At the 2001 Saskatchewan Soil Conservation Association's (SSCA) annual meeting, SSCA's membership passed a resolution opposing the introduction of Roundup-Ready wheat due to concerns over management of volunteer plants in direct seeding systems.

Rationale

Over the past two decades, agricultural producers and agrologists have recognized the potential of low disturbance seeding systems to minimize soil erosion and increase soil organic matter levels. However, these systems did not become economically viable until the late 1980s when Roundup (glyphosate) prices were lowered, and improved seeding equipment and improved management systems were developed. Soil conservation extension and demonstration programs over the past decade have encouraged producers to adopting these practices in large numbers. Over 30% of the seeded area in Saskatchewan was seeded using direct seeding by 2000.

Direct seeding and other conservation tillage systems rely heavily on glyphosate to control weeds prior to seeding and for chemfallow. In addition, glyphosate has become the herbicide of choice for long-term perennial weed control of several problem weeds. The introduction of Roundup-Ready crops has resulted in new management considerations to control volunteer plants. This is particularly important in direct seeding systems where glyphosate replaces tillage for preseeding weed control.

Including a single Roundup-Ready crop like canola in rotations has not caused serious volunteer management problems since canola is very easily controlled by phenoxy herbicides (2,4-D, MCPA). However, growing two or more Roundup-Ready crops in a rotation increases the complexity of volunteer management. The degree of complexity is currently unknown. If Roundup resistant weed management becomes too complex or the treatments too expensive, it is likely that, to deal with this new problem, farmers will change their cropping system back to traditional tillage systems.

Questions to be addressed

SSCA's concerns about Roundup-Ready wheat revolve around controlling volunteers with the preseeding burnoff. Unlike canola, there is no readily available and inexpensive control option like 2,4-D. To be compatible with conservation tillage systems, a low-cost, non-residual control product is needed to mix with glyphosate and glyphosate/2,4-D. In addition, there are many unanswered questions on the dynamics of volunteer wheat that needs to be addressed.

  1. How will seed dormancy properties affect volunteer management?
  2. Will volunteers need to be controlled for only one year or two, or more years?
  3. What will happen to the seeds from in-crop volunteers? Will they contribute more seeds to the seedbank perpetuating the requirement to control these weeds? In other words, will escapes continue to supply a source of resistant plants that need to be controlled?
  4. Will selection pressure increase the proportion of glyphosate resistant plants?
  5. How will volunteer crop dynamics affect weed control costs?
  6. What is the potential for Roundup-Ready wheat to cross-pollinate a related weedy species?

The big question that needs to be answered is will the introduction of Roundup-Ready provide both short and long-term economic benefits to farmers without increasing their risk? Unfortunately, this question cannot be answered until more is known about the behavior of volunteer plants.