Control of <i>Neonectria ditissima</i> with copper based products in New Zealand

Abstract

New Zealand pipfruit crops require postharvest fungicides for control of European canker, caused by Neonectria ditissima. Fungicide efficacy trials to protect leaf scars from N. ditissima infections were conducted during autumn 2013 and 2014. Disease control of artificially inoculated leaf scars was achieved by single applications of copper oxychloride and copper oxide, but not copper hydroxide, applied at 4.3, 1.1 and 0.6 kg elemental copper/ ha respectively. Control of leaf scar infections by copper oxide (0.65 and 0.95 kg elemental copper/ha) was similar to control by captan. Leaf scars (0-10 days old) remained susceptible to infections up to 10 days after leaf fall; disease control was achieved by re-distribution of copper and captan fungicides onto new leaf scars. Disease control using copper oxide was consistent and similar to control using captan. The copper product, and concentration of elemental copper, are important for successful control of leaf scar infections by N. ditissima.

How much captan is required for wound protection of <i>Neonectria ditissima </i>conidial infection in apple?

“…The low expression of leaf-scar infections is disappointing, but this has occurred in other artificially inoculated and naturally infected leaf-scar experiments in the 2015 autumn-winter period (Dryden et al 2016;Walter et al 2017b). Normally, under New Zealand (Tasman) conditions, we would expect 10-20% of leaf scars to develop symptoms within 6 months of artificial inoculation Walter et al 2015;2017b) but in the 2015 autumn-spring period only 4.4 % of leaf scars expressed in the control treatment. This, however, was typical for the 2015 season (Dryden et al 2016).…”

“…age played a role in the susceptibility to infection. Weber (2014) and Walter et al (2015) showed that leaf-scar age <2 days did not affect disease development. The leaf scars inoculated here were 1-day-old.…”

“…New leaf scars were created by pulling leaves from the tree during leaf fall (24 May 2015). These were marked and brush-inoculated (20-30 µL spore suspension per wound) the following morning (25 May 2015) using freshly prepared N. ditissima inoculum (1 × 10 5 conidia/ mL), as described by Walter et al (2015Walter et al ( , 2017b. Upon drying, spray applications were made using a Stihl back pack mist blower.…”

“…The percentage of inoculated tissues (leaf scars, picking wounds, rasp wounds) developing symptoms was analysed with a binomial generalised linear model (GLM, McCullagh & Nelder 1989) with a logit link. Earlier research has shown that shoot incidence and lesion incidence are always very highly correlated (r>0.99, Walter et al 2015). Treatment effects were assessed both overall, and also, for the leaf-scar experiment, as a linear contrast of captan concentration.…”

Postharvest foliar nitrogen applications increase <i>Neonectria ditissima</i> leaf scar infection in apple trees

“…Leaf scars were created 10 days after treatment application by removing three (preferably senescent) leaves per shoot. Selected shoots were labelled and leaf scars marked with a paint pen (Walter et al 2015). In each plot, there were up to 30 shoots which were inoculated with a N. ditissima spore suspension (ca 1×10 5 conidia/ml), prepared from naturally occurring canker lesions, as described by Walter et al (2015).…”