This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

There were increasing demands on avocado growers to optimise fruit yield and quality, reduce chemical use, develop market opportunities and meet consumer expectations to remain competitive. An increase in public awareness and concern for the environment also led to an increase in demand for ‘safer’ food and more environmentally sensitive production methods.

The objective of this project was to identify sustainable orchard management practices that could be used by avocado growers across Australia; to conduct trials to evaluate the effectiveness of some of these strategies; and provide recommendations to the wider industry on the most promising practices.

Several orchard management practices and products were being used by avocado growers including: mulching, natural mineral fertilisers, fish and kelp concentrates, composts teas and other brewed microbes, molasses and branch scoring.

The effect of different mulches on tree growth, yield and fruit quality was investigated in Central Queensland over three consecutive years. Trees were mulched with filter-press (a sugar industry by-product), cane-tops and avocado woodchip at flowering during September each year. Mulching trees with avocado woodchip and to a lesser extent cane-tops increased cumulative yield compared with trees receiving minimal mulch. The increase in yield may have been due to the tendency for increased root growth observed in these mulched trees.

Trials investigating the effect of a range of soil and foliar treatments were also conducted. Foliar application of pyroligneous acid (PandA®) an organic liquid derived from heating bamboo to 250-350°C in combination with a copper fungicide treatment could increase fruit quality with a reduction in the incidence of fruit rots and disorders. Soil and foliar applications of microbial products (TwinN® & BB5®) could increase root growth in avocado. This increase in root growth and possible nutrient uptake may have been responsible for improvements in shoot growth, tree health and fruit quality observed at some of the experimental sites.

The effect of branch scoring on fruit size and yield was investigated at several sites across Australia. Scoring involved cutting a groove no more than 3mm wide around the branch to sever the phloem using a knife or pruning saw. Results indicated that branch scoring may have provided a non-chemical approach for increasing cropping in vigorous avocado trees, particularly in southern growing regions. However this technique was still experimental and may not have necessarily worked under all growing conditions.

Although results of this work demonstrated some improvements in tree growth, yield and fruit quality further discriminatory testing on these sustainable management practices was necessary before grower recommendations could be made.