|Abstract or Summary
- In previous research in Europe, asulam (methyl sulfanilylcarbamate)
was found to be a potentially useful herbicide for controlling
broadleaf dock Rumex obtusifolius L. ) in permanent pastures.
Asulam was also reported to have a low margin of safety when used
on common pasture species. Field studies were conducted in western
Oregon to examine broadleaf dock control obtained at asulam rates
that would not reduce pasture yield and to determine the optimum
time of asulam application for dock control. Field, greenhouse, and
laboratory studies were conducted to determine the tolerance of
perennial ryegrass, tall fescue, orchardgrass, bentgrass, white
clover, and subclover to asulam and to examine a possible change
in protein content of grass forage after asulam application.
Control of broadleaf dock was studied at three rates and four
application times of asulam. Asulam was applied at 1. 0, 1. 5, and
2. 0 lb/A in April, May, June, and July. Results from early applications were superior to later applications of asulam. The
April treatments were applied to dormant or slowly growing dock
in the crown period. Control was good at all rates. The May treatments
were made to actively growing dock late in the crown period
or early in the rising period. Season-long control was good, but
control of regrowth was not acceptable, particularly at the lower
rates. June and July asulam treatments gave poor control of broadleaf
dock at all rates.
Pasture species differed in tolerance to asulam. Perennial
ryegrass was the most tolerant grass and white clover was the most
tolerant legume examined. Perennial ryegrass, tall fescue, orchardgrass,
and white clover showed adequate tolerance to asulam, especially
at the 1. 0 and 2. 0 lb/A rates. These species suffered slight
yield decreases at 4. 0 lb of asulam/A. Bentgrass and subclover
were less tolerant to asulam. These species suffered more severe
injury and yield reduction at all rates of asulam than did the other
Field studies also showed that clipping affected pasture grass
tolerance to asulam. The effect of clipping was greatest in grass
species that were most tolerant to asulam treatment. Clipping before
asulam application increased injury to the sward. Injury increased
as the period between clipping and treatment decreased. Clipping
after asulam application reduced injury to the sward and increased speed of recovery.
Laboratory experiments were conducted to determine the effect
of asulam on the crude protein of tall fescue. Asulam caused a temporary
reduction in the rate of crude protein loss. This coincided
with a temporary growth delay observed in tall fescue after treatment.
Asulam did not reduce the crude protein content of tall fescue
at any harvest dates examined.
Asulam can successfully control broadleaf dock in western
Oregon pastures when applied at 1. 0 to 2. 0 lb/A in early spring with
little or no damage to swards containing a large percentage of tolerant
pasture species. Swards containing a large percentage of bentgrass
and subclover should not be treated with asulam unless serious yield
reductions can be accepted.