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Fruit & Orchards

Question: Pruning Black Rot Cankers in Apple?

16 years ago

Hi Everyone,

It's about six years since I planted my first apple trees and there's still so much to learn! Lesson one for this year appears to be about Black Rot (Botryosphaeria obtuse). If you have any experience/knowledge about how to deal with it, I would be thankful for your reply.

I have a couple apple trees that have some small, unbroken cankers that I suspect are from Black Rot. The appearance of the cankers is slightly reddish, like a watermark below the bark. If it matters, the cankers are not sunken. There are no visible fruiting bodies (black pycnidia).

I read that one should prune branches about 15" below cankers. Does it matter if they are small and not visibly open? I am wondering if I could excise the small cankers and halt the progression of the disease?

Black Rot & White Rot

Regards,

PoseyPlanter

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Comments (4)

jellyman
16 years ago
Posey:

Whether it is black rot or not, you are surely seeing something, and it is most likely fungal in origin. If these kinds of diseases are present in your area, you have a good reason to dormant spray your trees with a strong mix of copper at least twice on warmer, calm days during late winter or early spring. The best such product I know of is called Kocide, and I use it on all my trees every dormant season.

Copper can effectively prevent this disease, and a wide range of others, and even suppress them once they are established. Once the growing season is underway, copper becomes problematic to use since it causes leaf damage. I don't know of any other fungicide that would be effective against these types of diseases once the trees begin to leaf out, but you could consult your local nursery, and see if they carry anything that might help.

I don't think trying to physically excise the visible cankers would be very effective, and might cause the disease to spread further.

Don Yellman, Great Falls, VA
Posey Planter
Original Author
16 years ago
Hi Don,

Thank you for your reply!

I sprayed copper sulfate in the form of a 10-10-100 Bordeaux Mixture in mid-March this year. IÂm hoping to get in another application before the leaves open. I might have tried to spray this evening, but I held off since rain was forecast for afternoon today. It hasn't rained yet. I'll check the forecast again tomorrow and reassess.

Some of the trees show buds in green tip, others are still dormant or silver tip. IÂm hoping that after the rain, I may still be able to get in another spray. Even if I canÂt spray the buds, I can spray the bare wood since the espaliered trees are so open in form.

Thanks again:)

Regards,
PoseyPlanter
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And I got the technique from Bas Van Ende, but I've never used it on peaches or other stonefruit. I didn't trust the integrity of the wood enough but now I know I could. I do sometimes use spreaders, however. I don't generally use the first large branches for my scaffolds anyway, and remove them for branches of smaller diameter that are naturally more horizontal. This may reduce the size of my first crop but beyond that it's hard to slow down a healthy peach. Oversized branches tend to make weak unions and often break under cropload if left unsupported. My peach trees start life as central leaders and I don't convert them to open center until they've begun seriously cropping. The central leader also supplies a place for spreaders- the easiest way to make branches more horizontal. One other point about brown rot. It's very important to keep the fruit thinned in a way that they never touch. I guess you could even make sure that no leaves are touching the fruit so it dries quickly. Summer pruning will also help keep the fruit dryer if done with that strategy in mind.
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jellyman
16 years ago
Posey:

Bordeaux mixture is certainly better than nothing, but is no match for a copper hydroxide product like Kocide, which delivers a lot more fixed copper to the trees. I spent several years dissolving copper sulfate crystals to spray my trees with not much result. Using Kocide has made a significant difference to my trees, both stone and pome fruits.

Don Yellman, Great Falls, VA
Posey Planter
Original Author
16 years ago
Hi Don!

Thanks for the tip! I will check into it.

I greatly appreciate both your experience and generosity in sharing it:)

Regards,
PoseyPlanter

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