|Abstract or Summary
- Weedy rye (Secale spp.) is a weed in the winter-wheat- growing
regions in the Pacific Northwest and surrounding regions. Ethiazin
(4-amino-6-(1,1-dimethylethyl)-3- (ehtylthio)-1,2,4-triazine-5 (4H)-one)
has shown selective control of weedy rye in the cultivar 'Stephens',
(Triticum aestivum). Field, greenhouse, and outdoor pot experiments
were conducted to determine factors influencing selectivity.
Field studies were conducted in eastern Oregon in 1985-86 to
determine the optimum timing and rate to apply ethiazin for weedy rye
control, and also to see if the addition of metribuzin would increase
rye control while reducing the ethiazin rate. Stephens wheat tolerated
the herbicide treatments at all locations. Optimum timing for application
was the 2-3 leaf stage of rye for two of the locations. Application
at the 1-2 leaf stage was most effective at the remaining location.
Rye control was enhanced with increasing ethiazin rate. The addition of
metribuzin enhanced rye control at a lower rate of ethiazin. Wheat
grain yields, above ground biomass, and culm number of wheat increased
with increasing rye control.
Greenhouse and outdoor pot studies were conducted in Pendleton and
Corvallis, Oregon, through 1985-87, to identify factors influencing this
selectivity. Uptake experiments indicated that rye is more sensitive to
ethiazin through root uptake than through foliar uptake. In time-of-application
studies conducted outdoors, best control was at the one-,
two- , and three-leaf stage of rye. Control was lower at preemergence
and the four-leaf stage. Depth of seeding did not affect sensitivity of
rye to ethiazin.
Immersing roots of wheat and rye seedings into ethiazin solution at
various concentrations showed Stephens to be 13 times more tolerant than
cereal rye to ethiazin. This indicates that selectivity between wheat
and rye seen in the field is primarily due to physiological differences.
From a management standpoint, this is greatly preferable to selectivity
based on differences in retention on the foliage, rooting depth, crown
depth, and other morphological factors.
Weedy rye appears to be taxonomically different from the cultivated
species (Secale cereale). Wild and weedy rye were equally sensitive to
ethiazin when tested in a solution bioassay.