New Zealand Plant Protection 66 (2013): 386
Tomato potato psyllid (TPP) (Bactericera cockerelli) vectors Candidatus Liberibacter solanacearum, a phloem-limited bacterium that can cause a mottled browning discolouration ('zebra chip'; ZC) in fried crisps. Sulphur is mainly used as a fungicide but is also registered in New Zealand as an insecticide against erineum mite (Colomerus vitis) on grapes. A field trial to determine TPP response to foliar-applied sulphur found that weekly applications (no insecticides) significantly reduced psyllid nymph numbers in foliage compared with the control (no-sulphur + no-insecticide). However, the incidence of severe ZC in fry-cooked tubers was higher in the weekly sulphur treatment than with a commercial insecticide spray programme. Tubers from both the non-sprayed control and the weekly sulphur treatment had significantly lower yields and specific gravities than those treated with insecticide. Sulphur applied alternately with insecticides gave similar results to the commercial insecticide programme - promising for the industry's goal of reducing insecticide applications.
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