Pasture control techniques for the establishment of mountain ash (Eucalyptus regnans) plantations.  P. C. Fagg.  October 1985.  39 pp. (unpubl.)

SUMMARY

Four trials were commenced in 1980 and 1981 to evaluate 9 herbicides in 36 different combinations of type, rate and method of application, for the control of pasture on land being reforested by the planting of mountain ash (Eucalyptus regnans F. Muell.) in the Strzelecki Ranges, Yarram Region, South Gippsland. Prior to planting, the trial sites were prepared by ripping with or without scalping.

Knock-down and residual, pre-emergent herbicides were applied alone and in mixture, pre- or post-planting, using strip spraying (controlled droplet application-CDA) and spot treatment (spotgun and rope-wick wiping) techniques.

Taking tree height and mortality 21 months after planting as measures of success, several treatments gave significantly greater height growth than the manually weeded or untreated controls, without substantially increased mortality. Considering both herbicide and application costs per planted hectare, the cheaper, effective treatments included:

pre-planting                                                 spot                       strip

amitrole (2 kg ha^-1)+ simazine (3 kg ha^-1)   $65 ha^-1                   $76 ha^-1

amitrole (2) + dalapon (5)                          $64 ha^-1                   $74 ha^-1

post-planting (to bare soil)

propazine (6)                                             $78 ha^-1                 $120 ha^-1

propazine (1.5) + propyzamide (1.5)           $87 ha^-1                 $149 ha^-1

The study clearly demonstrated the benefits (in terms of increased growth and longer weed control) of including residual herbicides, such as propazine or simazine, with knock-down herbicides, such as amitrole or glyphosate, for pre-planting applications, by either CDA or spot-spraying. For post-planting applications, a pasture knock-down herbicide to which mountain ash is tolerant was not identified; though it would be possible to shield the planted seedling from the spray or use the wiping technique (when grass is short). Split applications of knock-down (pre-planting) and residual herbicides (post) are feasible, but probably not economical.

Results also indicated that the 'triazine growth stimulation effect' may have occurred, and that mechanical scalping may have been partly responsible for reduced growth compared with ripping alone.

As both spotgun and CDA applicators each have their own specific advantages in costs and usage, the choice of technique for applying herbicides will depend largely on formulation, weather conditions, terrain, and whether pre- or post-planting application is required.

Further research is needed to identify selective, knock-down herbicides for overspraying eucalypts planted in pasture.