Competition from brush is only part of the brush problem in areas due for reforestation. Brush is fine habitat for animals that feed on tree seedlings. Moreover, in heavy stands of brush, dead or alive, substantial shade will weaken trees and considerable debris can fall and crush small seedlings. It is always best to provide for reforestation before brush becomes well established, and to avoid suppressing conifers by controlling fast-growing species such as alder and maple when they are in seedling or young sprout stages. If weeding is needed, it is always most effective if the planted trees are never exposed to competition. Site preparation is the most important step in avoiding the weed problem.
Two or more herbicide applications may be desirable for full plantation establishment. Schedule them so that most woody competitor species are controlled the summer before planting (often better before harvesting) with a site-preparation treatment. After planting, maintenance spray with a soil-residual material such as atrazine or hexazinone prolongs brush relief with minimum damage to conifers (see "Recommendations for Grass and Forbs in Plantation Establishment" in this section). Never postpone release until trees are under the brush.
Some commonly used herbicides are injurious to conifers at high doses or during the growing season. Control difficult weed problems before planting, as part of site preparation. Both Imazapyr and sulfometuron near the maximum label rate can be injurious, even when used as directed. Use maximum rates only in exceptional circumstances. The potential exists for stunting injury when imazapyr is applied broadcast over labeled western Oregon conifers at more than 3 oz ai/a.
Several precautions will minimize damage from foliage-active products when used for conifer release.
1) Adding surfactants to any herbicide used for broadcast release can increase the risk of conifer damage.
2) Using maximum registered rates of foliage-active products for conifer release often produces symptoms of injury in conifers, so use these rates only when attempting to control hard-to-kill species and when some conifer injury is tolerable.
3) When applying foliage-active herbicides with ground equipment, do not spray directly into desirable seedlings and saplings because doing so causes "hot-spots" of heavy application that can result in injury and even mortality.