RESEARCH & EVENTS
Update on Monterey Decline
Dr Len Tesoriero 1 and Dr Tonya
Wiechel 2
1
Crop Doc Consulting Pty Ltd, 2 Agriculture Victoria
FOLLOWING recent seasons of extreme wet conditions, Monterey almond trees across the Sunraysia and Riverina regions have exhibited widespread bud and leafing failure, shoot dieback, and, in some cases, tree death. In the NSW Riverina, affected trees continue to decline. This past season, symptoms included trunk gumming and cankering— potential signs of Phytophthora infection— along with gumming nuts and shoot dieback. Diseases such as Anthracnose and Bacterial Spot were confirmed on affected nuts, and wood rot fungi were detected in dieback tissue, suggesting that stress-related physiological decline may interact with multiple pathogens. Late-season leaf yellowing and drop have also been common in Monterey trees, likely due to water stress resulting from deficit irrigation practices aimed at accommodating other varieties. Monterey trees are particularly sensitive to both excess and limited water availability. This sensitivity is linked to lower nonstructural carbohydrate reserves in Monterey trees compared to other varieties, as observed in U. S. studies. When stressed by water issues and subsequent leaf loss, Monterey trees may not store enough starch to support spring growth, flowering, and leaf-out— especially given their high yield potential and late nut maturity, which further deplete carbohydrate reserves. The AL22002 project has focused on investigating potential plant pathogens associated with what is now termed Monterey Decline( MD). Surveys across affected regions found no unique pathogens responsible for MD, although common ones were present. In controlled trials, potted Monterey trees inoculated with these pathogens showed no MD symptoms after one season, indicating that while pathogens may contribute, they are unlikely the primary cause. To support grower responses, the AL22002 team has collaborated with the ABA communications
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ABOVE: Monterey decline symptoms in Sunraysia – late season Anthracnose infection.
LEFT: Moist incubated trunk sections of potted Monterey trees inoculated with isolated pathogens.
30 In A Nutshell- Winter 2025 Vol 26 Issue 2