Poplar trees, if grown as a crop, don’t have one thing that most agricultural crops in North America depend on for viability – legal herbicides.
Appropriate herbicides are available but they aren’t registered for use on tree plantations.
Cees Van Oosten of SilviConsult Woody Crops Technology Inc. of Nanaimo, B.C., is a tree production veteran.
“Being able to control weeds in a hybrid poplar stand is no less important than controlling competition in any other crop. Lost plant resources are lost. End of story,” he said.
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There is a growing interest from western Canadian agricultural producers in fast growing trees for future markets such as lumber, biogas, composite hardboards and pulp.
Deb Weedon of the Saskatchewan Forest Centre said most of the interest in raising trees on the Prairies is coming from farmers rather than wood processing companies, especially when it comes to marginal farmland,” she said.
Gary Coghill of Saskatchewan Agriculture estimates that 3.18 million acres of marginal farmland in the province’s black and grey soil zones might be appropriate for growing trees.
Agrologist Larry White of the forest centre said one of the hurdles for converting that land to hybrid poplar production is the lack of registered crop protection products.
Van Oosten said glyphosate is the only herbicide registered for use in tree plantations “and you wouldn’t want to go and spray that across a whole field of trees.”
Producers can now use Trifluralin, Sencor and Lontrel for post-emergent and residual weed control in shelterbelts, but the products are not registered for use when the trees are planted as a crop.
Van Oosten has applied to the Pesticide Management Regulatory Agency for a minor-use permit for Lontrel.
The agency recently created a new minor-use category of pesticides aimed at existing, licensed products that would be used in such small amounts for a specific application that chemical manufacturers wouldn’t deem it affordable to do the full set of trials required for registration.
White said weed control in the first three to five years of the plantation is all that is required for a stand of trees with a 20-25 year harvesting date.
“Many of our weed problems on the Prairies are only made worse with tillage. That is the other reason we need these minor-use registrations,” he said.
Van Oosten has completed studies with wood company MacMillan Bloedel that show proper weed control during the establishment years of a hybrid poplar crop can double or triple the volume of wood produced in those years.
“It’s simple. Any leaf area on the ground takes away from leaf area on the tree. Less leaf area on the tree results in less production,” he said.
