Abstract

Summary Nine different herbicidal chemicals were applied in 36 different combinations of rate, time and application technique for the control of herbaceous weeds where Eucalyptus regnans (mountain ash) was being planted in South Gippsland. Knock-down and pre-emergence herbicides were applied alone and in mixture, pre—and post-planting, using strip spraying (controlled droplet application) and spot treatment (spotgun and rope-wick wiping) techniques. Twenty-one months after planting, several treatments gave significantly greater height growth than the manually weeded or untreated controls without substantially increased tree mortality. The cheapest, effective pre-planting treatments included amitrole+simazine (2+3 kg ha−1), amitrole+dalapon (2+5 kg ha−1) and glyphosate+simazine (1+3 kg ha−1). Two of the better post-planting treatments were propazine (6 kg ha−1), and propazine+propyzamide (1.5+1.5 kg ha−1), applied to predominantly bare soil. For pre—planting weed control, the study demonstrated the benefit (in terms of increased tree growth) of applying pre-emergence herbicides, such as propazine or simazine, together with knock-down herbicides, such as amitrole or glyphosate, by either strip or spot spraying. For post-planting weed control, E. regnans should be shielded from amitrole or glyphosate, or alternatively a wiping technique can be used, although neither was successful in the study, as the treated pasture was too tall. The selectivity, efficacy, and cost-effectiveness of the studied herbicides and application techniques are discussed.