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Summary of full report
by Keith Lewis and Michael Gorton
June 2004
RIRDC Publication No 04/064 RIRDC Project No SAG-3A
Executive Summary
At Atherton, in 2002, three
replicated field trials were conducted to evaluate the insecticidal properties
of tea tree oil. The target pests were heliothis (Helicoverpa spp.)
infesting Sebago potatoes, and common foliar pests of cabbages (cv Green
Giant). The cabbage pests assessed were cabbage white butterfly (Pieris
rapae), diamond back moth (Plutella xylostella), heliothis (Helicoverpa
spp.), cabbage centre grub (Hellula hydralis) and cluster caterpillar
(Spodoptera litura).
Two trials were conducted in potatoes and a single trial was carried out in cabbages. All the trials were designed as replicated complete blocks with four replications. The active constituent, raw tea tree oil, was applied at 1.0, 2.0, 3.0 and 4.0 L/ha to potatoes, and at 100, 200, 300 and 400 mL/100L in the cabbage trial.
In two potato trials there was no control of heliothis after two spray applications at a five day spray interval. In both cases, the larvae were small at application, and would be considered to be sensitive to conventional insecticides. The larval population developed unchecked, with progressively fewer small larvae and increasing numbers of larger larvae being observed in all treatments.
In cabbages, the results were similarly poor, and no treatment effects on pest numbers, feeding behaviour or development were observed.
It was concluded that tea tree oil was not suitable as an insecticide for the control of leaf eating caterpillars in potatoes or cabbages.
 
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