NAME OF THE ORGANISM: Neonectria ditissima (NECTGA)

Neonectria ditissima has been reported from more than 60 tree and shrub species in diverse orders (Flack & Swinburne, 1977; CABI, 2021). Economic damage attributable to this pathogen is most severe on apple and to a lesser extent on pear - known as European canker of apple and pear (Van der Scheer, 1980; CABI, 2021). It has also been recorded on a large number of other woody hosts including Cydonia and Juglans (Smith et al., 1988).
An important pathway for Neonectria ditissima is via the two types of spores it produces: conidia (asexual spores) and ascospores (sexual spores). Conidia are generally produced within the first year of canker formation when the temperature increases in the spring and summer and are spread throughout the season by rain splash. Ascospores are mainly produced by old canker lesions during the autumn, winter and spring and are discharged during rain, and wind- or splash-dispersed. Both spore types enter through wounds, either natural such as bud-scale scars, leaf scars, fruit scars or artificial, such as pruning wounds. Thus, inoculum and points of entry on the tree are available all year round and the main limiting factor is rain, which is essential for spore production, spread, germination and infection (Xu et al.,1998; Amponsah et al., 2015; Gómez-Cortecero et al., 2016). Ascospores enable the fungus to undergo long-distance dispersal whereas both ascospores and conidia may spread the fungus within an infected tree or between adjacent trees.
Regions where it rains in over 30% of days/month and temperatures of 11-16°C are attained for an average of >8 h/day are at greater risk for European canker of apple. Areas at higher latitudes (>52°) with frequent summer rainfall appeared to be most prone to European canker (Beresford & Kim, 2011).
In an experimental design, budded apple rootstocks of three nurseries were planted at three different sites and observed for development of Neonectria ditissima for over two years. For two sites the trees showing infection were at the periphery of the orchard, indicating that most of the inoculum came from outside the orchard, probably from a neighboring orchard (McCracken et al., 2003). However, as explained in the article, this experiment was set up in a location and climate highly conducive to between-orchard spread.
Long distance natural spread may depend on local conditions: results from Weber & Borve (2021) supports the view that ascospores do not play a major role in the disease in current Northern German apple production.
The fungus can also travel with budded rootstock (McCracken et al., 2003). Weber & Børve (2021) reports about infections in orchards (Norway) emerging because of infection in nurseries. In this review it is suggested that N. ditissima is capable of surviving prolonged latency periods within the apple tree trunk, causing symptoms and sudden decline e.g. after 2 years. Infections of nursery trees which do not become visible as cankers until the second growing season or beyond are particularly troublesome for the fruit farmer.
Because Neonectria ditissima is widespread in Europe (also on many natural hosts other than Malus, Pyrus, Cydonia, Juglans), the influence of conducive weather will generally limit the role of propagation material infections compared to natural spread. However, the Fruit SEWG concluded that under some climatic conditions, plants for planting may remain a significant pathway e.g. in Finland and Northern Germany (Weber & Borve, 2021). The Fruit SEWG highlighted that research is hampered by the difficulty and cost to assess the role for long distance spread by ascospores.
Seeds are not considered to be a pathway for Neonectria ditissima (CABI, 2021).
Remark: A ‘substantially free from’ requirement will prevent cankers from being present on plants for planting.

In the responses to the questionnaire, FR commented about the 'Very strong presence in Atlantic orchards' and how it is 'difficult to control because few effective fungicides'. However, experts considered that solution was more related to cultivar selection.

From NIAB (the page also provides a list of appropriate fungicides).
In problem orchards routine treatments are required every year. Effective control of canker requires an integrated approach with both cultural and chemical treatments.
• In winter, prune out cankers where possible or pare back cankers on scaffold branches to healthy tissue. Treat with a suitable canker paint immediately after pruning.
• If possible remove prunings from orchard and burn. Otherwise pulverise or macerate pruning debris taking care that pieces do not remain beneath the trees on the herbicide strip.
• In summer prune out shoot dieback as soon as possible to reduce inoculum for fruit rot.
• On young trees ensure that wounds are painted.
• In orchards with low canker incidence at autumn leaf fall, apply a spray of a copper fungicide (check status of current authorisation) at 10% leaf fall and repeat at 50% leaf fall.
• In orchards with moderate to high canker incidence apply a spray of tebuconazole (Fathom, Folicur) before the end of leaf fall, followed by a spray of a copper fungicide at 10% leaf fall, then a spray of tebuconazole (Fathom, Folicur) at 50% leaf fall with a second copper spray at 90% leaf fall.
• Apply a pre-bud burst copper spray in the spring.
• In planning the use of copper sprays, growers should check the current approval status and permitted number of applications of copper fungicides.
• At bud burst spray dodine (e.g. Radspor 400, Syllit 400 SC) or a dithianon based product (Dithianon, Delan Pro) to protect bud scale scars against infection. Repeat at mouse ear.
• Thereafter use dithianon based products or captan as part of the scab control programme. These products will give some protection against canker.
• Dithianon + pyraclostrobin (Maccani) or pyraclostrobin + boscalid (Bellis) or cyprodonil + fludioxonil (Switch) will also give some control.
• Orchards at risk from Neonectria rot can be identified in spring based on the incidence of cankered trees in the orchard (<5% = low risk, 5-25% = moderate risk, >25% = high risk) and the rot history from pack house records. The risk of Neonectria rot in store can then be further assessed based on the rainfall between blossom and harvest.
• Apply sprays of captan or pyraclostrobin + boscalid (Bellis) or cyprodonil + fludioxonil (Switch) to orchards where a moderate to high risk has been identified, during blossom and at petal fall. These will give fruit some protection against Neonectria rot and in orchards with a high canker incidence, are essential if fruit is to be stored without significant losses beyond Christmas.
• The same treatments can be applied pre-harvest in late July and August.
• In orchards where a high canker risk has been identified, the best option may be to avoid chemical treatment and schedule the fruit for early marketing before Christmas to Minimize losses.
• The Neonectria risk of fruit from lower risk orchards is based on the volume of rainfall from blossom to harvest. In seasons when rainfall is above average this fruit may also need to be scheduled for early marketing if sprays have not been applied during blossom.