Vol. 51—1997 - NorthEastern Weed Science Society

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hexazinone residues than that experienced by multipot seedlings. Presumably, bareroot
seedlings were more vulnerable to these residues when first planted, since their root systems
were more distur~ed than multipot seedlings. Collectively, the New Brunswick and Ontario
results suggest that soil texture, organic matter content, stock type, and planting time all play
roles in determiniPg black spruce seedling survival, and that the use of containerized
seedlings may help reduce seedling mortality due to hexazinone exposure.
Several so/vival differences, attributable to formulation (i.e., liquid vs. granular, 2 kg
ailha) were observed throughout this study. For seedlings planted 1 yr after spring treatment
with hexazinone,llowest survival was achieved with the liquid formulation. Wood et al. (26)
reported that sujival of bareroot and containerized black spruce planted in the spring
following winter site preparation with PRONONE was not adversely affected by application
rates up to 6 kg *ilha, whereas both types of seedlings were damaged by dosages of more
than 2 kg ailha oifYELP AR L when planted within 4 weeks of a spring herbicide treatment.
Both hexazinonejapplications occurred at nearby sites within northern Ontario's Clay Belt
Region. They sIfculated that this discrepancy may have resulted from differences in the
formulations used, and that hexazinone released from PRONONE granules may have entered
the soil more slo/Wlythan hexazinone contained in the liquid formulation. Despite differences
in timing for the jtwo Ontario applications, the present results seem to confirm that there is a
difference in blaek spruce seedling survival associated with the use of the 2 formulations.
Althoughl significant differences in raspberry control affected by formulation were not
observed, Mino~ue et al. (9) reported that treatment with liquid hexazinone resulted in better
hardwood control and loblolly pine growth than treatment with granular hexazinone, for soils
with less than 60% sand content. Mean sand content for soils in this study was
approximately 3~%, and may explain why greater growth and lower survival were observed
with the liquid fbrmulation. Seedlings planted 1 yr after site preparation with liquid
hexazinone dempnstrated lower survival than granular treatments, but grew the most, due to
lesser amounts of raspberry competition.
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We conclude that spring treatment with PRONONE lOG (2 kg ailha), with planting
delayed by approximately 1 yr, provided the best treatment to achieve both optimal black
spruce seedling furvival and growth during the establishment phase of the plantation (21).
Poor survival (i.e., less than control seedlings) was observed for seedlings planted 1 month
after spring treatment. Better survival was most often observed with the granular
formulations th~ with liquid hexazinone, for seedlings planted 1 yr after hexazinone
treatments. Sinfe 5th-yr survival and stem volume for the 10% granular and liquid
formulations di1 not differ, operational needs should be considered when selecting the best
treatment. Operationally, a typical aircraft can treat more hectares per load with the
PRONONE 10