Efficacy and optimal timing of low-volume aerial applications of copper fungicides for the control of red needle cast of pine

Abstract

Background: Red needle cast (RNC) is a foliar disease of radiata pine (Pinus radiata D.Don), caused by Phytophthora pluvialis Reeser, Sutton & E.Hansen and occasionally Phytophthora kernoviae Brasier, Beales & S.A.Kirk. The disease has impacted plantations in New Zealand since at least 2008. To develop management recommendations for red needle cast, research has focused on identifying chemical control options and understanding pathogen epidemiology to guide optimal timing of spray application. The objectives of this study were to: (1) assess the efficacy of aerial copper fungicide application for the control of red needle cast in mature radiata pine plantations; and (2) investigate optimal spray timing. Methods: To address these objectives, three operational-scale field trials were undertaken in successive years between 2017 and 2019 at a forest in the Central North Island of New Zealand. RNC severity was assessed in canopies of forest blocks exposed to cuprous oxide applied at 0.855 kg ha-1 active ingredient in low-volume aerial spray at different times of the year (November, February and April (or May)). Needle cast from plantation trees and infection levels on trap plants were also assessed in some years. Results: Application of cuprous oxide significantly reduced RNC severity in all three trials. As well as reducing disease severity, application of cuprous oxide also tended to reduce needle cast from plantation trees and infection on trap plants in years when these were also assessed. No consistent effect of spray timing was observed. Generally, all three spray timings reduced disease severity compared to the unsprayed control, but differences were not always significant, and few differences were detected between different spray timings. Conclusions: The results reported here are the first to show that low-volume aerial applications of cuprous oxide applied at 0.855 kg ha-1 active ingredient can reduce the severity of RNC in commercial radiata pine plantations. No consistent effect of spray timing was detected. These findings support the development of management recommendations for RNC.

Infection periods of Phytophthora pluvialis and Phytophthora kernoviae in relation to weather variables and season in Pinus radiata forests in New Zealand

“…Recent research indicates that one or two aerial spray applications of copper fungicide as early as November in the disease cycle are effective in reducing disease levels, as also are later applications (Fraser et al 2022). The factors regulating disease outbreak years are still being determined, but it may ultimately be possible to advise when or when not to spray if weather conditions prior to the development of an epidemic govern the amount of initial inoculum.…”

“…Chemical control studies have shown that a copper fungicide used routinely to treat dothistroma needle blight, caused by the ascomycete Dothistroma septosporum (Dorogin) M.Morelet, in New Zealand radiata pine plantations can also be effective against RNC under controlled conditions (Rolando et al 2014(Rolando et al , 2017(Rolando et al , 2019 and in plantations (Fraser et al 2022). Research is proceeding towards the development of recommendations for operational aerial spray applications (Fraser et al 2022). In order to assist this work, detailed knowledge of the epidemiology of both Phytophthora pathogens is needed (Hood et al 2017).…”

Lessons from insect and disease impacts on radiata pine (Pinus radiataD. Don) plantations in New Zealand over the last hundred years

“…RNC usually passes after 2–3 years and does not lead to tree death (Figure 9). It can be controlled by copper sprays at low application rates (Fraser et al 2022, Rolando et al 2019), and tree breeding for resistance holds promise (Dungey et al 2014, Graham et al 2018). Both Phytophthora species also are known to be able to infect fine roots of radiata pine although the significance of this finding is unclear (Scott et al 2019).…”