3 minute read
Novel approaches to controlling apple canker
NIAB’s Matevz Papp-Rupar and Scott Raffle describe the latest research on apple canker, which is hoped to reduce the severe impact of the disease.
Apple canker caused by the pathogen Neonectria ditissima, continues to give rise to 10%-20% tree losses per year in young orchards, in the early years after establishment, and it is still considered one of the highest priorities for research by UK apple growers.
Previous NIAB research funded by AHDB (Project TF 223) used the biocontrol product Trianum G (Trichoderma harzianum) in newly planted orchards and stoolbeds. The product showed some promise in reducing the incidence of canker development, but it is currently only authorised for use on protected crops. This project also demonstrated that secateurs incorporating a chemical dispenser to treat pruning wounds, achieved significant reductions in canker number. Applying Folicur (tebuconazole) either alone or in combination with BlocCade (a physical acting barrier to spore germination) gave best results.
A more recent AHDB project led by NIAB at East Malling demonstrated that a Trichoderma based biocontrol product and a conazole based fungicide offered some decrease in canker incidence on infected trees, but only at lower inoculum levels of naturally infected wounds. As the biocontrol product is only authorised for use on grapevines and the conazole fungicide is not currently authorised on any crops in the UK, further research is urgently required.
Working with Agrovista and Avalon Fresh, NIAB is currently benefiting from a Growing Kent & Medway funded research project to explore novel approaches such as biocontrol, alternative spray programmes, and soil amendments for improved tree health and resilience, with the hope of improving canker management practices.
The first objective is assessing the use of commercial mycorrhiza and Trichoderma based products applied to newly planted Gala orchards in both drought and waterlogged prone soils to improve tree establishment. Canker incidence, tree mortality and tree growth will be recorded every six months to compare treatments.
The second objective is seeking to find ways of increasing natural populations of mycorrhizal fungi, which are believed to improve soil drainage, soil health and nutrient uptake, to enhance tree health, tree growth and the ability to withstand pathogen infection. Some wildflower species which are known to support the growth of naturally occurring and introduced mycorrhiza are also being established to measure their impact, whilst a modified root pruner supplied by Agrovista which dispenses mycorrhizal inoculum directly to tree roots during root pruning, is being investigated.
Finally, a range of novel substances are being assessed in a newly planted orchard which has been artificially infected with apple canker (Neonectria ditissima) at a high inoculum level. Products authorised for use in the UK but not currently on apple are included, along with biocontrol products with antimicrobial properties, which are being applied both with and without biostimulants and defence elicitors. The results from the Year 1 trial indicated that hydrated lime (e.g. building grade Hydrated Lime Blue Circle) applied three times (20%, 50% and 80% leaf fall) at the rate of 50kg per hectare in 300 litres of water, significantly reduced canker incidence. The results are in line with the research findings from The Netherlands where this approach is used in overhead irrigation. In Year 2 the dose and timing of hydrated lime application will be optimised and tested in combination with other products.
