In-vitro efficacy of various fungicides against fungi associated with leaf, stem, and soilborne diseases of Proteaceae in Hawai'i, USA

Authors: Luiz, Blaine; Sugiyama, Lionel; Bushe, Brian; LUTGEN, HANNAH - University Of Hawaii; Keith, Lisa

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2024
Publication Date: 9/24/2024
Citation: Luiz, B.C., Sugiyama, L.S., Bushe, B.C., Lutgen, H., Keith, L.M. 2024. In-vitro efficacy of various fungicides against fungi associated with leaf, stem, and soilborne diseases of Proteaceae in Hawai'i, USA. Plant Health Progress. 25:353-357. https://doi.org/10.1094/PHP-04-24-0033-SC.
DOI: https://doi.org/10.1094/PHP-04-24-0033-SC

Interpretive Summary: Since the 1960's, Proteaceae species have been important ornamental plants in Hawaiian agriculture, cultivated for both cut flowers and foliage. Numerous diseases have been identified on protea in Hawai‘i and many of these affect the marketability of the cut flowers, foliage, and health of the plant. Efforts were made, through this in vitro study, to identify products that are effective at inhibiting the growth of several known and potential pathogens of protea. Results suggest that a rotation of fungicides could be used for disease management against a broad range of pathogens infecting Proteaceae in Hawaii.

Technical Abstract: Species in the Proteaceae have been important ornamental plants cultivated for both cut flowers and foliage in Hawaiian agriculture since the 1960's. Symptoms ranging from spots on leaves and flowers, to branch lesions and cankers, as well as dieback have been reported on various Proteaceae in Hawai‘i and attributed to various fungi. Nurseries can experience significant economic losses if symptoms are not controlled. Few studies are available regarding the effectiveness of chemical treatments to reduce disease incidence and severity. The efficacy of six ornamental fungicides of varying chemical groups was tested in vitro for their ability to inhibit the mycelial growth of nine fungal isolates (genera Diaporthe, Alternaria, Neofusicoccum, Neopestalotiopsis, and Calonectria) recovered from symptomatic stems, leaves, and soil from diseased Proteaceae grown at the Maui Agricultural Research Center (MARC), Kula, HI and from several commercial farms on Maui. Every fungicide tested in this study inhibited some, if not all, of the nine isolates to varying degrees. Tebuconazole provided the broadest control, inhibiting growth of all isolates by >85% or more compared to mycelium growth on control plates. This initial screening suggests that a rotation of fungicides could be used for disease management against a broad range of pathogens infecting Proteaceae in Hawai'i.