Graduate Thesis Or Dissertation
 

Efficiency of forest vegetation control with herbicides

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dj52w798m

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  • Selective suppression of crown and root sprouting of non-coniferous cover are the keys to effective forest vegetation management. This study 1) develops insight into mechanisms of controlling root suckering and top regrowth of bear clover (Chamaebatia foliolosa), and develops a broad data base for controlling broad groups of vegetation chemically. Finally, it develops a mangement guide for use of this technology to achieve certain management objectives. Four herbicides were evaluated for their ability to control post-treatment resprouting of bear clover. Sprouting was evaluated above and below ground by creating trenches to expose the rhizome network. Soil moistures were also studied to determine if their were differences due to varying levels of efficacy. They were marginally responsive in the top 60 cm of soil. Plant moisture stress measurements were obtained on ponderosa pine (Pinus ponderosa), and were found considerably more responsive than surface soil water contents. Several application parameters including volume, dose, surfactant, dropsize and product were studied to determine their influence on herbicide efficacy and efficiency on several Pacific Coast species of shrubs and grass. Sites included the Oregon Coast Range, the east side of the Oregon Cascade Range and the west side of the Sierra Nevada Mountains in California. Growth regulator products were not suitable for long-term control. High levels of sprouting were observed above and below ground. Glyphosate led to control of above-ground sprouting as well as the rhizome system of bear clover. Sprouting was found to increase with increasing distance from healthy vegetation. Glyphosate was much less effective on other evergreen species. Herbicide treatments in April were more selective between evergreen shrubs and ponderosa pine than those in June. Surfactant increased pine damage while decreasing selectivity. Drop size was related to pine damage in general but degree of effect varied with geographic location. Dose was found to be the single most important factor contributing to response. Application parameters other than dose generally did not contribute to efficacy except that large drops enhanced growth regulator effects on manzanita on the east side of the Cascades, as indicated by a second order interaction between dose, surfactant and nozzle. The addition of surfactant to growth regulator products in April and to glyphosate in June also increased absolute efficacy on Sierran brush species. Soil residual products did not respond in important ways to application technology. Salmonberry also did not respond to dropsize or surfactant. The information obtained was incorporated into a management guide for efficient herbicide use.
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