Alternative fungicides for controlling husk spot caused byPseudocercospora macadamiaein macadamia

Abstract

Abstract. Husk spot, caused by Pseudocercospora macadamiae is a major fungal disease of macadamia in Australia. Chemicals to control the disease are limited and frequent failure to control the disease is a major concern to growers. The overall goal of this research was to improve the chemical control strategy of P. macadamiae through the provision of fungicides with different modes of action to carbendazim, which is the current industry standard. Husk spot incidence, premature fruit abscission, kernel quality and yield were evaluated following application of different fungicide products in replicated field experiments at three different sites. Results showed significant differences in disease incidence and premature fruit abscission between fungicide treatments, field sites and years. Generally, disease incidence and premature fruit abscission on trees treated with fungicide were significantly (P < 0.05) lower than the untreated control. Pyraclostrobin conferred significantly better protection than trifloxystrobin, reducing disease severity by 70% compared with a 50% reduction by trifloxystrobin. The pyraclostrobin treatment had a similar efficacy to the current industry standard (70% reduction cf. 73% reduction by tank-mixed carbendazim and copper). Higher amounts of immature kernels occurred in the untreated control, followed by difenoconazole and trifloxystrobin. Diseased fruit accounted for 78% of premature fruit abscission, which indicates that husk spot enhances fruit abscission in macadamia. Our results suggest that pyraclostrobin provided similar efficacy to the industry standard and could, therefore, play a key role in the management of husk spot.

Fungicide control of Gnomoniopsis smithogilvyi, causal agent of chestnut rot in Australia

“…Both fungicides have shown significant effects in controlling other ascomycetes under Australian field conditions. For example, pyraclostrobin and difenoconazole significantly reduced the incidence of husk spot disease in macadamia caused by Pseudocercospora macadamia (Akinsanmi et al 2008). Similarly, the use of pyraclostrobin and difenoconazole reduced significantly the severity of the disease caused by Corynespora cassiicola (brown spot) and Asperisporium caricae (black spot) in papaya (Vawdrey et al 2008).…”

Genetic parameters of husk spot resistance in macadamia breeding families

“…Pedigree-based mixed models were used to account for unbalanced components of the trial design and enable exploitation of all available data. In previous studies, husk spot-induced abscission was typically measured by comparing kernel maturity of abscised nuts in symptomatic and asymptomatic trees Akinsanmi et al 2007Akinsanmi et al , 2008Miles et al 2010aMiles et al , 2010b. Kernel maturity assessments have been favoured because of their direct relevance to on-farm profits Akinsanmi et al 2007).…”

“…Nevertheless, these results provide a baseline of information to support future selection strategies. Such information is important as husk spot data is often difficult to obtain due to issues such as variable nut-set (Miles et al 2010b) and/or insufficient disease pressure (Akinsanmi et al 2007(Akinsanmi et al , 2008.…”

Efficacy of the biocontrol agent Trichoderma hamatum against Lasiodiplodia theobromae on macadamia

“…When mature, typical conidia are 1-septate, brown and measured 26–31 × 12–16 μm ( Fischer et al, 2017 ). Although macadamia cultivation still relies on the use of synthetic chemicals like carbendazim and pyraclostrobin ( Akinsanmi et al, 2008 ; Khun et al, 2021 ) to minimize disease problems, there is a broad trend to explore and develop biocontrol agents, including the use of beneficial fungal endophytes, to manage tree diseases ( Sosso et al, 2021 ).…”