Testing Herbicides for Tree Safety and Efficacy in Conifer Nurseries

Weeds are a significant challenge in forest tree nurseries. Few herbicides are currently registered in conifer nurseries, with none providing complete weed control. Two trials were therefore conducted to generate data to support future herbicide registrations. In the first trial, 22 herbicide treatments were applied to freshly transplanted Douglas-fir (Pseudotsuga menziesii Mirb. Franco) seedlings. Weed control was initially excellent, but waned with some treatments 3 to 4 months after treatment. Douglas-fir foliar injury was excessively high with several treatments though seedlings had largely recovered by harvest, with most growth measurements not differing from nontreated Douglas- fir. In the second trial, 13 herbicide treatments were applied in July to yellow fieldcress ( Rorippa sylvestris [L.] Besser), a particularly difficult perennial species to control in conifer nurseries, then all plots were late-winter fumigated followed by transplanting to Fraser fir (Abies fraseri [Pursh] Poir.) or noble for (A. procera Rehder) seedlings the following May. Only imazapyr gave acceptable initial control of yellow fieldcress, reducing weed cover from an average of 20 percent to 2 percent 2 months after treatment. Four months after planting (14 months after application), however, seedlings exhibited significant injury from soil-residual imazapyr. This paper was presented at the joint annual meeting of the Western Forest and Conservation Nursery Association and the Intermountain Container Seedling Growers’ Association (Troutdale, OR, September 14–15, 2016).

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Author(s): Tim Miller

Publication: Tree Planters' Notes - Volume 60, Number 2 (2017)

Event: Joint Annual Meeting of the Western Forest and Conservation Nursery Association and the Intermountain Container Seedling Growers Association
2016 - Troutdale, Oregon

Volume: 60

Number: 2