Keep Plum Trees Healthy and Productive With Summer Pruning

, written by Ann Marie Hendry gb flag

Summer pruning plum trees

Plum trees may produce generous harvests of some of the most mouth-wateringly juicy fruits, but they’re not without their problems. They often tend towards what’s known as biennial or alternate bearing, where trees produce a bumper crop one year, only to take the following year off. Cropping so prolifically can also cause branches to become so weighty that they actually snap under the strain.

There are also two serious diseases to be aware of. Silver leaf and bacterial canker can weaken or even kill plum trees.

These issues are heartbreaking when they occur, but the good news is they can usually be avoided by carefully performing one simple annual maintenance task: summer pruning.

Silver Leaf Disease in Plum Trees

Silver leaf disease can affect other fruits such as apples and cherries, as well as some other trees and shrubs, but it is most usually associated with plums. In autumn and winter, spores of Chondrostereum purpureum may infect trees through wounds, so it’s important to avoid pruning at this time.

“Silver
Silver leaf disease is spread by spores from a bracket fungus. Photo by Jerzy Opiola

In summer the leaves of infected plums take on a silvery sheen (although the leaves themselves are not infectious), then once the wood dies the bracket-shaped fungi appear, ready to produce more spores. They are a whitish colour, with a woolly surface and purplish-brown underside.

Environmental stress can cause a similar silvering, but it’s likely to affect the whole tree, not just selected branches as with silver leaf. Cut through a branch for a certain diagnosis. Branches infected with silver leaf will have a tell-tale dark stain at the centre.

Bacterial Canker in Plum Trees

Bacterial canker is another serious disease that affects plums and other trees of the same plant family (Prunus). It’s harder for the trees to resist the disease in winter, so again summer pruning is the safer option.

“Bacterial
Bacterial canker affects plums, cherries and other trees in the Prunus family. Photo by Rosser1954

Sunken, dead and often oozing areas of bark will become apparent from spring and early summer, and shoots may die back. Branches can quickly die of this disease. In summer small holes appear in the leaves. They look like they’ve been used for shotgun target practice, giving the disease its alternative name of ‘shothole’ (careful how you say it!).

Oozing bark, though alarming, isn’t necessarily a sign of the disease. It’s not uncommon on plums and related plants, and in the absence of the distinctive dead, sunken patch it’s likely due to other less serious issues, such as stress or a wound.

Summer Pruning Plum Trees

Thinning fruits can be regarded as the first stage of pruning, as it reduces strain on the branches. Do this in early summer while fruits are still small and can be pinched out with your thumb and forefinger.

July and August is the best time to prune plums in most Northern Hemisphere locations. Make sure your tools are sharp and sturdy enough for the job; secateurs can be used for very small twigs, but anything larger calls for loppers or a saw. It’s better to use a more powerful tool and make a clean cut than to struggle to force the blade of a lightweight tool through a thick branch.

“Pruning
Pruning in summer helps plums to avoid disease

Before any pruning task, stand back and take a look at your tree. The first thing to do is identify and remove the 3Ds – dead, diseased and dying wood. If you see signs of silver leaf, cut well beyond the area where the dark stain shows in the centre of the wood to make sure that no trace of the fungus remains.

Once that’s done, step back again and look over your tree. Do any branches point inwards, cross over each other or look like they’ll cross in the future? Branches that rub together will cause wounds, so they should be removed. Cutting them out sooner rather than later means you can make smaller cuts that are less likely to become infected. Soft shoots can be pinched out with your thumb and forefinger.

But remember, plums fruit on young wood. Avoid removing branches that are less than three years old unless you have to.

Choose a point just above a bud. Make your cut so that it slopes away from the bud to help rain to drip off. If you need to cut back to the main trunk, cut close to the raised ‘collar’ but not into it. Don’t leave a stub of branch sticking out – it will only die back and could introduce disease.

“Plum
Make pruning cuts to an upward-facing bud to prevent branches from drooping too much when heavy with fruit

Some plum varieties, like ‘Victoria’, tend to grow branches that spread outwards horizontally. These branches begin to droop when they’re heavy with fruit, and are liable to break. Make sure to choose upward-pointing shoots to counteract this.

Don’t use a wound paint or wrap to try and seal the wound. This used to be the recommendation, but best practice nowadays is to leave pruning wounds open to ‘bleed’ and heal naturally. This is healthier for the tree, unless there is a recurring issue with silver leaf or other diseases.

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Comments

 
" I have some kind of insects in my fruit trees in Rio Linda CA they remind me of Lady Bugs but usually all I find is a molted shell attached to the leaf. Do Lady Bugs molt? I also have little webs in my Blueberry bushes, leaf curl and something that lakes fruit tree leaves look like lattices. What if anything can I spray my trees and bushes with? thanks, Jon"
Jon Threet on Saturday 9 May 2020
"I think my plum tree has curly leaf. How can this be treated?"
Ray Marshall on Sunday 10 May 2020
"Hi Jon. Lady bugs do molt between their pupal and adult stages. It's possible your blueberry bushes have spider mite - we have a spider mite guide, please use the search box at the top of the page to search for it. For your other plant problems, sorry, it's hard to say as many things could cause the problems and depending on where you are in the world and which plants are affected the culprits might differ. I wouldn't advise spraying anything on your plants, and especially not while they're in flower or fruit. The best way to cope with pests - especially if you're not sure what they are - is to build up a resilient ecosystem in your garden by growing a range of flowering plants and avoiding the use of pesticides as these will kill beneficial bugs as well as the pest species."
Ann Marie hendry on Tuesday 12 May 2020
"Ray, leaf curl on plums is usually caused by aphids. Often they don't cause too much damage, although it may not look pretty. However if the problem is severe, wait until winter when the tree is dormant then use a winter tree wash. This should reduce or eliminate problems next year."
Ann Marie Hendry on Tuesday 12 May 2020
"I have a few amber coloured droplets on a few branches of my plum tree. when I touch it, it is hard, although I emagined from the look of it, it would be sticky. Is this somthing to be worred about? Regards Ray"
Ray marshall on Friday 22 May 2020
"Ray, it's probably just some sap leaking out from a small injury. I wouldn't worry unduly about it unless the area around it looks diseased or sunken."
Ann Marie Hendry on Friday 22 May 2020
"I have a Victoria plum tree and never had any plums from the free in10yrs I was advised to remove some of the branches from the trunk a few years ago.I have plenty of flowers on the tree and get small plums about the size of a pea then they drop off. I believe the tree has cancer can I remove the branch now in middle of June"
James on Monday 15 June 2020
"My Victoria plum tree has never developed plums over 10 yrs The plums drop off the tree when they are the size of a pea.The leaves have holes in them and it has signs of canker. Can I remove the branch in mid June"
James on Monday 15 June 2020
"Hi James. When plum trees drop very small fruits like that, it's usually a sign of insufficient pollination. This could be due to few insects flying at flowering time (for instance if the weather is cold or otherwise poor, or following insecticide use), or no pollination partners close by. 'Victoria' is technically self-fertile, but pollination will be much improved by having a pollination partner. Normally July to August is the recommend time for pruning plum trees if you're in the Northern Hemisphere, so just to be safe you might want to wait another couple of weeks. Prune out the affected branch, and if the tree is quite overgrown it may be worth thinning it a little to improve airflow."
Ann Marie Hendry on Tuesday 16 June 2020
"My plums, probably Santa Rosa, will be around Early July. The tree has many tall none fruiting limbs at the top of the tree. I trim them back normally after fruit is harvested but is there any value in trimming those branches back now In mid June so “more energy” can go to the plums."
Wendy on Tuesday 16 June 2020
"If yields are normally good I'd be inclined to leave pruning until after harvesting Wendy. The leaves on those branches will be gathering energy through photosynthesis, so removing them at this stage could (theoretically, at least) result in a net loss of energy. But if you feel yields are lower than they should be, by all means give it a try and compare with previous years. "
Ann Marie Hendry on Tuesday 16 June 2020

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