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Apple canker is a disease caused by a fungus, Neonectria ditissima, which attacks the bark of apples and some other trees, causing a sunken area of dead bark and, eventually, death of the branch. New cankers form from mid-spring, and once formed are present all year. Cankers can also develop on the trunk.
In perennial cankers there is an interaction between fungus and tree. At some periods the canker spreads whilst at others the bark grows back over infected tissues. Sometimes the canker stabilises or heals but, more usually, it spreads gradually until the branch is girdled, or so weakened that it breaks.
In the end I decided to be cautious this year, and opted for the first cut. That way I could keep my options open: if the wood below the cut is clean then I could leave it there or, if there were signs of the canker spreading deeper into the tree, I could make another cut further down the trunk.
The bark of a healthy fruit tree is sufficient to prevent an attack of canker. However, whenever the bark is damaged by pruning or attack by disease it offers the potential for the spores of canker to enter and establish themselves.
Another key identifier of canker is the presence of small areas of spores on the bark orwhere it is cracked. The spores form into small patches with a slightly gooey appearance which are red in summer and early winter but creamy coloured in spring.
SPRINGWhen the temperature increases in spring the spores multiply and begin to damage the flesh of the apple tree. Initially no external damage may be present. In spring the spores can sometimes be seen as creamy white small spongy areas in and around cracks in the bark.
LATE SUMMER AND EARLY AUTUMNThe canker further damages the tree and new spores, typically now seen as reddish in colour, will be spread by the wind to new sites. The spores can travel several metres on the wind and infect nearby trees.
CORRECT PRUNINGSee ourpage on pruning apple trees for an in depth description of when and how best to prune apple trees andthis page for pruning pear trees. As far as avoiding canker when pruning each year is concerned, the key point is to always sterilise pruning equipment before pruning a tree and afterwards. If pruning more than one tree sterilise the equipment when finishing with each tree. Properly developed canker is easy to spot but in its initial stages there may be very few or no external signs.
The copper fungicide Bordeaux Mixture has previously been recommended as a spray to prevent canker in fruit trees. However it has now (or soon will be) withdrawn from sale in the UK. Currently there are no alternatives which have been scientifically proven to be anywhere near as effective as Bordeaux Mixture
The only proven method of treating canker is to remove all infected wood and bark by pruning it out. If the canker is in a stem or branch this means cutting off the branch or stem below the site of infection into good clean wood. Infected wood is brown whereas clean wood is creamy green. Leave not one ounce of infected wood on the tree if you want to eradicate canker completely. Sterilise tools before and after pruning of this type and burn all pruned wood and foliage - ALL of it!
If canker affects the main trunk of the tree below a certain level it's clearly not an option to prune off all the tree. In this case you have a stark choice, either dig up the tree and start again with a new one (the option a commercial orchard would take) or to perform surgery on the trunk.
Rather than go into endless words on how to this we have found an excellent and instructional video (see end of this page) fromHuw's Nursery on how to this. See also the picture below of canker affecting the main trunk of an apple tree.
Figure 1 Density plot with number of main stem canker lesions per tree on horizontal aixs and proportion of trees on vertical axis (the final May 2021 assessment). Seven apple scion cultivars planted at three sites where trees were planted either in December 2018 or cold-stored and planted April 2019.
Table 3 Estimates of variances for all random effect factors in the linear mixed model analysis of canker data on individual scion cultivars summarised over individual plots across three sites where trees were planted either in December 2018 or cold-stored and planted in April 2019.
Figure 2 Mean number of main stem canker lesions on individual trees of seven apple scion cultivars across three sites and four assessments (Autumn 2019 (1), Spring 2020 (2), Autumn 2020 (3), and Spring 2021 (4)) Trees were planted either in December 2018 or cold-stored and planted in April 2019.
Table 4 Sum of squares of the fixed effect factors in the linear mixed model analysis of canker data on individual scion cultivars summarised over individual plots across three sites where trees were planted either in December 2018 or cold-stored and planted in April 2019.
Figure 3 Mean number of main stem (A) and peripheral canker (B) lesions per tree of seven apple scion cultivars across three sites and two planting times. Four assessments were: Autumn 2019 (1), Spring 2020 (2), Autumn 2020 (3), and Spring 2021 (4).
Figure 4 Density plot of number of peripheral canker lesions, when assessed in Spring 2021, of individual trees of seven apple scion cultivars planted at three sites where trees were planted either in December 2018 or cold-stored and planted in April 2019.
Figure 6 Incidence of healthy, nearly dead, and dead trees for each combination of cultivar and site (tree heath was assessed in Spring 2021). Seven apple scion cultivars were planted either in December 2018 or cold-stored and planted in April 2019.
Figure 7 Overall incidence of healthy, nearly dead, and dead trees across all scion cultivars and sites (tree health was assessed in Spring 2021). Seven apple scion cultivars were planted either in December 2018 or cold-stored and planted in April 2019.
Citation: Xu X, Passey T, Robinson-Boyer L, Mclean H, Saville R and Papp-Rupar M (2022) Development of European apple canker on different cultivars in relation to planting time at three sites in the UK. Front. Hortic. 1:995776. doi: 10.3389/fhort.2022.995776
Apple canker is a serious disease which needs to be identified, and, if present, it has to be eliminated from young trees. It is caused by the fungus Neonectria ditissima (also known as Neonectria galligena or Nectria galligena). Infections can be initiated both in spring-summer, by means of spores dispersed by water from the creamy pustules that form at the edges of an existing canker, and in winter and spring, dispersed by airborne spores released by raised red pustules.
This method of control has to be completed by no later than the end of October. A second check of the treated wounds should be carried by the end of March, before the trees get into leaf. Watch a video tutorial on how to cut out canker.
TABLE 1. Main factor effects and significant two-way interactions from four-way ANOVA analyses of apple (Malus pumila) performance metrics from a 3-year growth experiment; the four main factor effects tested are (1) arbuscular mycorrhizal fungal (AMF) inoculation (AMF inoculation or non-inoculation), (2) nutrient addition (low or high), (3) scion type (Dabinett or Michelin), and (4) rootstock type (MM106 or MM111).
TABLE 2. Treatment means and SE for metrics of apple (Malus pumila) performance from a three year growth experiment; percentage differences between the two levels of each of the four treatments (1) arbuscular mycorrhizal fungal (AMF) inoculation (AMF inoculation or non-inoculation), (2) fertiliser addition (low or high), (3) scion type (Dabinett or Michelin), and (4) rootstock type (MM106 or MM111), are also presented.
FIGURE 1. Root colonisation of apple trees (Malus pumila) inoculated with two species of arbuscular mycorrhizal fungi (AMF). Mean AMF colonisation after 3 years of growth under high and low nutrient treatments and for both Dabinett and Michelin scions is presented. Error bars represent SE per treatment (n = 20). AMF colonisation was significantly affected by both scion type (P < 0.05) and nutrient treatment (P < 0.001) but not rootstock type.
FIGURE 2. Mean total dry above and below ground biomass for apple trees (Malus pumila) grown under high and low nutrient treatments. Error bars represent SE per treatment (n = 24). Below ground biomass was significantly affected by nutrient treatment (P < 0.01), scion type (P < 0.01), and rootstock type (P < 0.001). Above ground biomass was significantly affected by rootstock type (P < 0.05) only.
FIGURE 3. Total apple tree (Malus pumila) material infected by the fungal pathogen Neonectria ditissima. Trees were grown with and without inoculation with arbuscular mycorrhizal fungi (AMF). Error bars represent SE per treatment (n = 20). Total pathogen infected material was significantly affected by AMF inoculation (P = 0.001), scion type (P < 0.001) and rootstock type (P < 0.001).
Previously, several toxins were isolated from culture filtrates of V. mali. They were identified as degradation products of phlorizin, including p-hydroxybenzoic acid, p-hydroxyacetophenone, phloroglucinol, 3-(p-hydroxyphenyl) propionic acid, and protocatechuic acid, and are responsible for the symptoms of Valsa canker (Koganezawa and Sakuma, 1982; Natsume et al., 1982; Wang C. et al., 2014). Five isocoumarins produced by V. mali were also shown to promote the infection of V. mali on apple trees (Okuno et al., 1986). Remarkably, secondary metabolism-related genes are remarkably expanded in V. mali and are significantly upregulated during infection (Ke et al., 2014; Yin et al., 2015). These findings prompt us to speculate that SMBGCs probably play essential roles in V. mali infection. However, which SMBGCs are involved in virulence or toxin production is still undefined. 59ce067264