What was it all about?

From 2017 to 2022, this project provided accurate, up-to-date knowledge of the cause and expression of economically significant almond diseases to inform the development of effective management strategies. An updated disease guide for almond growers was developed, which will be made available on the Almond Board of Australia website along with other resources such as fact sheets and presentations.

The research team conducted disease surveys in 2018-2020 in the major almond production regions and identified hull rot, trunk diseases, Phytophthora and lower limb dieback (LLD) as diseases of importance.

Significant correlations were found between these diseases, agronomic practices and weather conditions.

Extensive field trials were conducted investigating the factors affecting hull rot caused in Australia by Rhizopus sp. Variety and rootstock had a significant effect, as well as water availability. Mummy nuts only had a weak association with hull rot. The Ceres Imaging predictive tool based on thermal and multispectral imaging showed promise for identifying locations with high disease risk. Pathogen-produced fumaric acid, which contributes to hull rot strikes, was influenced by water and nitrogen treatments. Management trials found that currently used fungicides reduced hull rot but did not eliminate it. The product diKaP™, a nutrition and stress tolerance product previously investigated in California, had a similar success rate. 

The research found that LLD is unlikely to be caused by trunk disease pathogens alone. Other factors include tree age, light interception, cultivar, and management practices.

Pathogenicity trials were conducted using seven different trunk disease pathogens. All species caused disease, some more consistently than others. It is also likely that factors such as water, nutrition and temperature affect canker development. Phytophthora and Phytopythium species were also tested, with many found to be aggressive pathogens. No effect of cultivar was seen among the six cultivars tested.

Of 23 fungicides tested in vitro against truck diseases, nine progressed to orchard trials, and four were identified as potential wound protectants. In vitro and detached fruit, assays identified the three fungicides most effective against Rhizopus. One biological agent also acted comparably to many chemical treatments.

Economic analysis showed that grower actions to combat disease were economically beneficial but varied with the disease. Treatments for trunk diseases had a positive economic benefit, whereas the benefit of treatment for hull rot depended on the cost of the fungicide.