Fungicides and an insecticide tested for the control of wattle rust and brown wattle mirid in Acacia mearnsii plantations

Black wattle is planted on 110 000 ha in South Africa, and considered economically important for both private and commercial growers. Black wattle is intensively managed, with protection from abiotic and biotic risk factors forming an important component of any management strategy. Of the various pests and diseases, brown wattle mirid and wattle rust have a negative impact on early wattle growth. Although pesticides have been shown to be effective for their management, the opportunity to combine an insecticide and fungicide in the same tank and applied as a mix would reduce operations. In November 2017 four trials were initiated on contrasting black wattle sites in KwaZulu- Natal, South Africa. Azoxystrobin + tebuconazole (Custodia®) were tested at varying rates, timing (November or January) and in combination with cypermethrin (Kemprin®) for the control of the wattle mirid and rust on different site types. Azoxystrobin + difenoconazole (AmistarTop®) were included as a reference standard, and an untreated control for comparative purposes. Tree growth, tree condition and disease/insect expression assessments over one growing season were used to determine optimum treatments. The fungicides and rates at which they were tested were equally effective for the control of wattle rust. Custodia® when applied at either 1.2 or 2 L ha⁻¹ showed similar trends to AmistarTop® (1 L ha⁻¹) in terms of optimum tree performance/condition, together with fewest wattle rust symptoms. Although there were tree performance benefits associated with the curative application of a fungicide after infestation (January 2018), spraying before infestation (November 2017) provided the greatest benefits. Wattle mirid presence in three trials indicated tree performance benefits when controlled with an insecticide. However, greater benefits were obtained when combined with a fungicide for the control of both wattle mirid and rust. Applying the two as a tank mixture would reduce costs without a noticeable impact on the efficacy for either active ingredient.