Testing alternative synthetic and natural insecticides for the management of foliar insect pests on two Eucalyptus species in the KwaZulu-Natal Midlands

Dlamini LS, Little KM and Sivparsad BJ
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Two trials were implemented in the KwaZulu-Natal Midlands in October 2016 (at Ingwe and Balgowan plantations), to test the efficacy of eight different insecticides (synthetic and organic) for the management of foliar insect pests. The Ingwe trial was planted with Eucalyptus dunnii and the Balgowan trial was planted with Eucalyptus badjensis. The insecticides tested were azadirachtin, deltamethrin, imidacloprid (liquid and tablet), Beauveria bassiana, Bacillus thuringiensis, potassium silicate and a combination of plant oil extracts (garlic oil, soybean oil and capsicum oleoresin extract). The imidacloprid tablet, deltamethrin and an untreated control were implemented as additional treatments. The insecticides were tested at the recommended rate (single rate) and at double the recommended rate (double rate), except for the insecticides in the additional treatments which were only tested at the single rate. These insecticides were applied three times over a period of four months, and tree growth measurements (Dbh and Ht) were taken four times over a period of seven months. Gonipterus spp. was the only insect pest found in both these trials, thus the insecticides were tested for their efficacy in managing this specific insect pest. A higher population of Gonipterus spp. and its damage was found in the E. dunnii trial and very little to no damage was observed in the E. badjensis trial. The insecticides tested were not effective in managing Gonipterus spp. in these specific sites. A low population of insect pests and incorrect timing of application could offer a plausible explanation of results.