Abstract:
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.
