Contributed Abstract

A comparison of dichlobenil four per cent granular and dichlobenil fifty per cent wettable plus a polymer extender for use as a fall applied perennial weed herbicide by W.D. Richards, Research Supervisor, Pacific Coast Nursery Inc., Route 1, Box 320, Portland, Oregon 97231.

A trial was established at Pacific Coast Nursery Inc., Sauvie Island, on 4 deciduous tree varieties to determine the comparative effectiveness of 1 herbicide in 2 different formulations. The first formulation was a 4 per cent ai granular material and was applied alone. The second formulation was a 50 per cent ai wettable material and was applied in conjunction with a polymer extender at a 1 to 1 ratio. All 4 of the shade tree varieties were grown in the field from seed and were transplanted in the test area on May 11, 1979. These plants were white birch, cockspur hawthorn, littleleaf linden, and thornless honeylocust. The trees were planted in commercial rows 4 feet apart on a 1 foot spacing and the treatments were applied in an 18 inch by 12 foot plot and were replicated 3 times for each variety. The herbicides applied to each variety were dichlobenil 4G at 3.75 Ib ai/A and diclobenil 50W at 5 Ib ai/A plus polymer extender in a 1 to 1 ratio. The treatments were applied on October 23, 1979.

Initial observations on weed control and crop tolerance were taken on December 20, 1979 with 2 subsequent checks made on February 25, 1980 and April 13, 1980. The plots were given a visual rating from 0 to 10 for weed control and crop tolerance. The weeds observed were annual bluegrass, chickweed, dandelion, foxtail, common lambsquarters, mustard, redroot pigweed, wild raddish, shepardspurse, and bull thistle.

The dichlobenil 4G proved to give only slightly better weed control than the dichlobenil 50W plus polymer extender and neither material caused any significant economic loss from crop tolerance. The materials should be compared in terms of cost and ease of application by the user.

• © 1981, International Society of Arboriculture. All rights reserved.