- HOE 23408 [methyl 2-[ 4-( 2, 4- dichlorophenoxy )phenoxy]propanoate]
is a herbicide used to selectively-control Italian ryegrass
(Lolium muitiflorum Lam.) and wild oats (Avena fatua L.) in wheat.
The objective of this research was to compare the relative importance
of foliar and root uptake of the herbicide in these two weed
species. Factors such as plant biotype, stage of plant growth, soil
type, irrigation type, and amount of soil moisture were examined.
Plants were grown in plastic pots in the greenhouse with a 12-
hour day, 12-hour night schedule. HOE 23408 (38% a.i. emulsifiable
concentrate) was applied using an overhead variable-speed sprayer
calibrated to deliver 309 L/ha. The herbicide was applied at three
placement sites: foliage only, soil only, and foliage plus soil.
Foliar placement was accomplished by protecting the soil with a
1.5 cm layer of perlite prior to spraying. This layer was removed
when dry. Soil only application was administered by pouring a 25 ml
solution of the herbicide directly onto the soil. The combination treatment was sprayed with neither area protected. Symptoms developed
within 2 to 4 weeks from the day of treatment. Fresh weights,
visual ratings of injury, and dry weights were obtained to assess
injury. Fresh weights gave the best injury estimate and were converted
to percent fresh weight reduction prior to analysis. Five
replications were used in each experiment.
Both foliar only and soil only applications of the herbicide
caused injury to both species. Italian ryegrass was more sensitive
to HOE 23408 than wild oats. HOE 23408 was applied at rates of .56,
1.12, 1.68, and 2.24 kg/ha. Injury increased with increasing rate
in all placement treatments.
The effect of the herbicide on ryegrass and wild oats was
examined under conditions of New Zealand and western Oregon. In
New Zealand, the high organic matter Canterbury Plains silt loam
greatly reduced soil activity of the herbicide. 'Tama' ryegrass, a
rapidly growing New Zealand variety, was found to be more sensitive
to foliar application than the western Oregon biotype. Ryegrass was
slightly more susceptible to the herbicide at the one- to two-leaf
stage than at the three- to four-leaf stage.
Ryegrass and wild oats were grown in western Oregon using
Woodburn silt loam (3.5% 0.M.), Newberg sandy loam (1.7% O.M.), and
silica sand (0.5% O.M.). Injury from a 1.12 kg/ha application of
the herbicide decreased with increasing organic matter content. No
differences were noted for foliar applications of the herbicide in
the different soil types.
Placement effects were examined under two irrigation types: subsurface and overhead. No placement x irrigation interaction was
noted. Plants subjected to subsurface irrigation grew more rapidly,
and consequently, the overall injury was greatest in these plants.
Two studies were conducted with ryegrass grown under various
soil moisture conditions: 120% Field Capacity (F.C.), 96% F.C.,
60% F.C., and 32% F.C. Neither foliage only nor soil only placements
were affected by soil moisture. However, HOE 23408 activity
in the combination treatment was significantly reduced under low
soil moisture conditions.
Ryegrass and wheat were grown in quart size glass Mason jars
filled with nutrient solution. The objective of this study was to
determine if root inhibition could be caused by either placement of
HOE 23408. The herbicide was applied either to the foliage or to
the nutrient solution. Measurements of the longest root were taken
daily. Root growth was severely inhibited only when the roots were
exposed to the herbicide, not when the foliage was treated.