n Southern African Forestry Journal - sensitivity to the application of pre-emergent herbicides applied at planting : scientific paper

Volume 2002, Issue 193
  • ISSN : 0038-2167



Five pre-emergent herbicides were applied either on their own or in various combinations to commercially planted <i>Acacia mearnsii&lt;/i&gt; De Wild. seedlings in the KwaZulu-Natal Midlands. <i>Acacia mearnsii&lt;/i&gt; growth responses to the protected or unprotected application of these herbicides were compared to a weedfree and weedy control. Compared to the weedfree control, suppression from weed competition only caused a significant reduction in tree growth from 92 days after planting, by which stage most of the residual capabilities of the herbicides tested had been reduced. The herbicides which did give good control of both grasses and volunteer wattle regeneration relative to the weedy treatment were oxyfluorfen alone, or when combined with thiazopyr or thiazopyr + metazachlor. When applied as an unprotected spray, only the herbicide combinations of simazine / terbuthylazine and metazachlor did not cause a significant reduction in tree growth. Although only significant at &lt;i&gt;p&lt;/i&gt; < 0,1 the herbicides of oxyfluorfen and glyphosate / simazine / terbuthylazine, when applied as an unprotected spray, caused a reduction in tree survival (arcsine transformed) when compared to the weedfree control. Tree variability was found to be a function of the presence or absence of weed growth and the method of herbicide application. Lower tree variability was exhibited in those treatments for which no pre-emergent herbicides were applied or where the seedlings were protected during spraying.

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