Mortalities of Eucalyptus marginata Donn ex Smith (jarrah) and E. calophylla R.Br. (marri) trees injected with Roundup™ (360 g glyphosate 1· 1 ) or Tordon Timber Control™ (50 g picloram 1· 1 and 100 g triclopyr 1" 1 ) (P+ T) were determined at doses of 5 to 80 grams of active ingredient (g.a.i.) m· 2 of stem basal area for glyphosate, and 2 to 40 g.a.i. m· 2 for P+ T. The effect of spacing of injections around the tree bole was examined. Seasonal variation in mortality was examined in relation to atmospheric vapour pressure deficit (v.p.d.) and soil water deficits.Glyphosate was more effective in killing E. marginata trees, whereas P+ T tended to be more effective in killing E. calophylla trees. The optimum doses of glyphosate and P+ T for E. marginata trees were 20 g.a.i. m· 2 and 15 g.a.i. m· 2 respectively, and for E. calophylla 80 g.a.i. m· 2 and 15 g.a.i. m· 2 respectively. Spacing of injections around the circumference of the tree did not have a significant effect on the mortality of E. marginata trees injected with glyphosate. However, mortality of E. calophylla trees injected with P+ T declined from 89% at 10-15 em spacing to 70% at 25-50 em spacing.There were strong seasonal effects with both herbicides and in both species, with mortality higher (70-90% mortality) in seasons other than summer (30-50% mortality). For E. marginata trees injected with glyphosate, mortality declined linearly with increasing v.p.d., from 95% at a v.p.d. of 0.5 kPa, to 25% at 4.5 kPa. For E. calophylla trees injected with P+ T, mortality declined linearly with increasing v.p.d., from 85% mortality at a v.p.d. of 0.5 kPa, to 50% at 3.0 kPa. Stem injection of both species should only be carried out when the vapour pressure deficit on the day prior to stem injection is less than 1.5 kPa.
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