While woody plants are still dormant and bark is very visible, its a great time to monitor for structural issues and overwintering canker diseases on ornamentals. Many of these cankers can still be pruned out and removed (and destroyed). However, once the canker disease can be found in the main stem, the tree is compromised and there is usually very little we can do.
Filbert blight (Anisogramma anomala) is fairly common on our ornamental hazel, such as Corckscrew hazel shrubs (Corylus avellana ‘Contorta’) and Turkish hazel trees (Corylus colurna). It is also a big problem in hazelnut production. The cankers release spores in early spring and the new emerging shoots are susceptible to infection. Warm, humid conditions favour disease infection and development. Once the new growth hardens off, it is no longer susceptible to infection. So by removing infested shoots before budbreak, you have an opportunity to reduce the chances of new infections. Prune out branches as far back as possible and remove/destroy. Protect new growth with fungicides before rain events.
Fireblight on apple (Malus) and pear (Pyrus) has been pretty significant since 2014. This bacterial disease is most successful during warm (>18oC) and wet weather. It overwinters inside infected trees and can show as a canker on branches and on the main stem (see video).
The overwintering cankers give rise to a sticky ooze in early spring that contains millions of Fireblight bacteria. The ooze is spread by rain, wind and insects and can cause primary infections of flowers and wounded tissues. Cankers are still dormant at this time and you can see the zone of necrotic vs. healthy tissue by shallow knife dissection.
So…..if you are seeing cankers on branches and/or the main stem of apple and pear trees, Fireblight could very well be the cause. Freeze-thaw injury is also possible. Lab analysis can confirm your diagnosis. Submit fresh intact canker samples so the lab can dissect the tissue and sample the leading edge of the canker for their analysis.
There are other types of organisms that cause cankers on woody plants, Botryosphaeria is a common pathogen that is often overlooked or misdiagnosed.
Botryosphaeria Canker is a common fungal disease of deciduous trees that we see in the landscape. Typically it is a disease of older, more established trees (not so much on juvenile nursery stock). Different species of Botryosphaeria can be found on different hosts. B. obtusa is the most common species, often found on fruit trees such as apple (Malus) while B. quercuum is found on oak (Quercus). Sinclair and Lyon (Diseases of Trees and Shrubs 2nd ed) report that Botryosphaeria is an opportunistic fungus that colonizes dead bark but can attack living twigs if the plant is under stress (wounds, freeze-thaw, pruning).
The nasty thing about Botryosphaeria obtusa is that it also causes black rot of fruit (above) and a frogeye leafspot (above) of foliage. Its a lot more common than you might think. I see it often together with apple scab. Frogeye leaf spot is a definite, brown necrotic spot in between the veins. (Whereas Apple scab causes diffuse-margin, subtle lesions on the vein, below). Infected branches, fruit and leaves from Botryosphaeria all give rise to gazillions of spores in spring and summer… that can lead to more infected tissue.
Botryosphaeria quercuum on oak behaves similarly, it infects killed or wounded branch tissue and can spread to colonize larger branch sections of stressed trees. As infected branch tissue becomes colonized, conductive tissue (phloem and young xylem) becomes compromised and some leaves will wilt, turn yellow and drop during summer.
Black, crescent shaped cankers will form in killed bark and eventually, the bark will fall off. It is really important to note that this disease can sporulate and spread from dead branches.
Botryosphaeria on oak is mainly a random branch dieback disease. It does not kill the tree. But it will slowly cause more and more branches to die over the years to come. It will sporulate on dead branches, which can be a major source of infection.
When ever you are dead-wooding trees in the landscape, COLLECT, REMOVE and DESTROY cankered looking twigs. It is very important to removed all diseased-looking dead branches from the site, especially while trees are still dormant.
Do ask the homeowner if they have been piling dead branches elsewhere on the property and get rid of them too.