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Abstract
Acacia mearnsii (black wattle) plantations in South African cover approximately 110 000 ha, with Uromycladium acaciae (wattle rust) found from Limpopo to the Western Cape of South Africa. This disease of black wattle causes reductions in growth, and mortalities with severe infections. Although a limited number of fungicides have been screened for the control of wattle rust, these contain similar active ingredients and need to be applied repeatedly to be effective. Not only is this costly, but there is also the possible development of fungicide resistance. In October 2015 a trial was initiated in southern KwaZulu-Natal to determine the effectiveness of varied application schedules and adjuvants of fungicide for the management of wattle rust. The main aim was to reduce the application interval. The trial was laid out in a randomised complete block design with three replicates. The 2 × 4 factorial combination consisted of two adjuvants application schedules (42 or 56 d between application) and four adjuvants (none; poly-1- p-menthene; borax + orange oil; poly-1-p-menthene and borax + orange oil). Three additional treatments were included where one was a control (no fungicides applied), and the other two additional treatments had fungicides applied according to the recommended 28-day schedule (one application commencing in October and the other in November). Wattle rust had a significant impact upon groundline diameter and biomass index but not height. All of the adjuvants and application schedules were effective in managing wattle rust, but did not increase the period before re-application was required. The most effective fungicide application used will therefore be based upon cost and in a manner that will reduce the likelihood of acquired resistance developing in wattle rust populations.