| Abstract |
- More than one-fourth of the forest land in the Pacific Northwest is growing timber at reduced capacity as the result of brush encroachment. Increasing use of chemicals in brush control requires that more information be available regarding their use. Bigleaf maple, Oregon oak and vine maple are among the more noxious brush species in the Willamette Valley area. This thesis summarizes the progress which has been made in the control of these species by the Forest Research Division. Aerial sprays have been found satisfactory in many areas for broadcast spraying of low brush cover. Basal sprays and ground level foliage sprays are used on weed trees and tall brush. Topography is also a major consideration in choice of method. Effectiveness of the herbicide is determined by climate, season, species, specific chemical, formulation, diluent, concentration, and many unknown factors. Most of the treatments in this project were applied to individual stems. Many of the tests were established in order to find the most effective chemical for a given situation; others expand on information gained in earlier trials. On large trees, applications were made both basally and in frills; also in bands around the boles at breast height with paste type herbicides. Smaller shrubs were treated with foliage sprays, dormant cane sprays, and individual stem sprays. The treatments were located on Bureau of Land Management land near Scio, Oregon, and in the McDonald Forest. Aerial spray projects conducted by the Bureau of Land Management in the Cascades and in the Coast Range have been included in these observations. Bigleaf maple was killed very successfully with basal sprays of 2-(2,4,5-TP) in oil in a mixture of 32 ahg. It is very likely that much lower dosages will prove adequate. Maple stems up to eight inches d.b.h. were well controlled with 2,4,5-T applied in a similar manner. Girdling has not proved to be an adequate method of control because of basal resprouting and delayed top-kill. Frilling followed with a dilute spray (22ahg) of 2-(2,4,5-TP) in kerosene gave good control. However, the cost of application is higher than for a similar basal spray. Paste herbicides were largely rather ineffective except for kilbrush applied in September. Oregon oak has proven more difficult to kill with basal sprays than maple. However, 2-(2,4,5-TP) and 2,4-D amine in frills have both provided complete top killing. 2-(2,4,5-TP) gave the better sprout control. Kilbrush gave good results on small stems when applied in August. Scarification of the bark prior to treatment proved to be the most dependable method. Vine maple has been top-killed by 2,4,5-T, 2-(2,4,5-TP) and brushkiller mixtures in many forms and concentrations. Sprouting has not been controlled completely by any of these but 2,4,5-T is the most effective in this respect. Aerial sprays of four pounds per acre of 2,4,5-T in some cases have caused nearly complete top-kill, and considerable sprout retardation. Snowbrush has been completely killed by 2,4,5-T with foliage and with step sprays. A Bureau of Land Management aerial spray project using four pounds per acre of 2,4,5-T gave 100 per cent kill of this species. Cherry, elderberry, thimbleberry, poison oak and madrone can be effectively top-killed with 2,4,5-T as basal or foliage spray. Sprout control has been relatively poor on most of these species. Grass competition to young seedlings can be reduced with several chemicals. Tree survival is consistently higher, however, when the minimum amount of grass herbicide is applied which will reduce grass density to approximately 60 per cent of normal. Soil sterilization reduces tree survival. The use of herbicides as a forest management tool has increased rapidly in recent years. Public acceptance of the value of this tool and further refinements in techniques can provide much needed relief for the brush problem in out forests.
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