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PLUM TREE PESTS AND DISEASES
Plum trees are one of the more resilient fruit trees and if the are given good care then they will most likely remain unaffected by pests and diseases.
Like all plants however things can go wrong and this page is designed to help you identify what the problem is and the best method of dealing with it.
Because plum trees can deal with a good amount of neglect many of the problems are associated with old age. Another cause of problems with plum trees is frost. Plant them in a frost pocket and the tree will survive but fruit will suffer.
In spring the sawfly emerges from the soil and lays eggs on the blossom of plum trees. When the plums begin to develop the little caterpillars eat their way into the centre of the plum and feed off it as the plum develops.
Look for the giveaway brown mark on fruits and when they are forming pick the fruit off and burn them, this will help in controlling the disease next year. Burn any fallen fruit which is unusable.
The chemical deltamethrin sprayed when the blossom is falling off will definitely help control sawfly.
Plum trees are often attacked by aphids and the first signs are young leaves curling up. They are not normally discoloured just curled. If you uncurl the leaf the aphids will be seen inside - small green, white or light brown insects. By themselves they probably won't cause too much damage but often they secrete a sticky juice which attracts unwanted diseases.
We have written a whole page on identifying and treating aphids and it can be found here. Follow that advice and almost certainly your plum tree will live through the attack with no bad side-effects. Two specific types of aphids attack plum tree, the Plum Leaf-Curling Aphid and the Mealy Plum Aphid. Both are treated exactly the same as other aphids. The Plum Leaf Curl tend to attack from April to June whereas the Mealy Plum Aphid attacks in July to early September.
NEW ARTICLE - JAPANESE
PINK MAGGOTS INSIDE PLUMS
This is caused by the caterpillar of the plum moth and makes the fruit
totally inedible. It's a particularly difficult pest to identify unless you
cut a plum open, or worse still bite into an affected plum. You will see a
pinkish small caterpillar / maggot inside with brown stuff in the hole it
has made inside the plum - that's its excrement!
Other signs are dried drops of gum which form near the entry hole, premature
fruit drop and discolouration of the plums.
There are chemical sprays which may help (use your favourite search engine to find one) but there is nothing that could convince me to spray chemicals over plums and then eat them. The alternative is the plum moth pheromone trap which attracts the male moths. The moths then stick onto the trap thus reducing the population of male moths. If you try this method follow the instructions exactly for the best effect.
Both Czar and Victoria plum trees seem to be particularly vulnerable to plum moth attack, other varieties less so. The lifecycle of this pest starts in May when the female moths lay eggs on the underside of growing plums. The eggs hatch and then dig into the plum and feed on it. When fully developed the caterpillar comes out from the plum and builds itself a small cocoon where it pupates (changes) into a fully grown moth. Favourite places for doing this are under cracks in the bark or on the soil below the tree.
Pigeons can be a real problem with plum trees (and cherry trees as well),
they first go for the leaves and rip them apart. They then start to damage
the new twig like branches, possibly simply because of the weight of the
birds perching on them although some believe the pigeons peck at them.
Either way the result is the same, leaves that are effectively destroyed and
major damage to newly growing stems.
The damage occurs typically in April to June time and the trees will fail to develop fruit in that year. There is no agreement as to exactly why pigeons do this. Preventing the damage depends to some extent on how big your plum tree is. Smaller plum trees can be protected with netting which is simply draped over the tree and this works well. Fruit cages are another permanent solution which prevent 100% of the damage.
For larger fruit trees, where it is not an option to surround them with a physical barrier, the options are more limited. Methods which have worked in some cases include those listed below:
- Hang old CDs from the branches to scare the birds
- Cut the bottom out of plastic bags and tie loosely to branches -
unattractive maybe but it seems to be the most successful way to scare
pigeons. The bags move about in the wind
- Plastic model of birds of prey tied high up on the tree and moved
occasionally. These can be bought online
One method which has been proven to be a failure is to try and attract the pigeons to other areas of the garden / allotment with bird food. What then happens is that more pigeons are attracted, they eat the bird food and then turn their attentions to the tree.
The symptoms of brown rot in plums are unlikely to be mistaken for any other disease. The skin of the affected plums will have grey, small raised bumps on it and if you cut into the plum the flesh will be discoloured and rotting where the bumps are most numerous. If left, the plum will shrivel completely. The picture below shows a plum affected by brown rot at a relatively early stage.
Insects, birds and fruit splitting because of lots of rain, all damage the fruits allowing this fungus to gain entry. Once a plum is infected it can infect other nearby fruit as well and very quickly the whole tree can become infected. Most at risk are plum trees that bear fruit very closely together (Victoria plum trees are particularly prone to Brown Rot) There are no chemical sprays available to the amateur gardener but if follow the action plan below this disease can be eradicated:
- As soon as you notice affected plums remove and destroy them.
- Remove and use any fallen plums, do not let them remain on the
- Pick fruit as soon as it is ripe, do not let them over-ripen on the
- If your plum tree is very tall with fruit high up that you cannot
reach then you have a problem. With trees of this size the plum fruit
higher up cannot be harvested and is a prime target for Brown Rot.
Invest in a pair of long-handled loppers and cut the highest fruit
bearing branches off. Late spring / early summer is the ideal time to do
- Thin the fruit on plum trees as recommended on this page. Too much fruit causes them to rub together allowing fungi such as Brown Rot to enter, it also prevents good air circulation.
The signs to look for are small green caterpillars on the leaves, buds which fail to develop and leaves with holes in them. This pest is the Winter Moth and will normally become apparent in late March to May. The first indication will be tiny caterpillars on and around fruit and leaf buds. They may spin silken threads and hang from the tree twigs. They then grow into larger caterpillars and will eat leaves, buds and almost all parts of the foliage.
Read our Winter Moth page for more details.
There are many forms of scale insects which attack a variety of plants but one in particular can be a problem with plum trees, it is named the Lecanium Scale. The picture below shows just how scary looking this pest is but, although serious if left to its own devices, it is not impossible to control. At maturity they look like pea-sized growths which are purple-brown on stems and young branches.
First, exactly what is it? What you see in the picture above is a scale insect which feeds on the sap of a twig, branch or leaf. Their life cycle begins when the scales overwinter and then lay eggs around May time - 200 or so eggs which are beneath the parents body. In May to mid July the eggs hatch and crawl away to new parts of the tree. This is the stage at which pesticides can be effective, when the insects are moving about. When the insects find a suitable position they clamp their jaws onto the bark of tree and begin to feed on the sap of the tree without moving again.
If you can identify the period in May /June when the young scale insects are on the move spraying with an insecticide will kill them. Ask at your garden centre for an appropriate spray. In general though, sprays suitable for killing aphids will also kill moving scale insects.
If you miss this stage of their lifecycle then a plant oil winter wash treatment (again ask at your local garden centre) in December to January will effectively suffocate many of the overwintering bugs.
The easiest method, if your tree is a manageable size, is to manually remove the scale insects around May when they are clearly visible but have not yet hatched their eggs. If you are squeamish about removing them with your fingers use a toothbrush and some diluted washing up liquid to brush them off. A gentle spray after with a hose should then remove all traces of them.
Relatively unknown in garden cultivated plum trees in the UK, Plum Pocket is becoming increasingly common. The symptoms are quite unusual and hard to mistake for any other pest or disease. Young fruit begin to to appear longer than normal and slightly larger, this normally becomes visible around mid June time. The next symptoms are white marks on the skin of affected plums, this is a fungus forming. Soon after the plums will begin to wither and die. Normally only around 50% of the plums are affected.
Both the picture above and below are courtesy of GardenFocused reader Walter A who is quite clearly a better photographer than I am! The above picture show young fruit on the right developing in the typical elongated fashion. The left hand plum is more developed and is clearly suffering from Plum Pocket.
If the fruits are cut open at any stage no stone will be found, just an empty "pocket" of white flesh as can clearly be seen from the picture above. As the plums wither they turn brown and fall off. The disease is caused by the fungus Taphrina pruni and affects plum and damson trees.
LIFE CYCLE OF PLUM POCKET
The spores of the fungi are spread through air and water from nearby affected trees. It is more commonly found on wild plum and damson trees so if you have any nearby take a careful look at them for signs of infection. The spores become airborne in early spring, land on your tree and lodge in the bark and newly forming branch buds. There they stay, causing no damage, until the next spring. They then multiply and begin to attack fruit buds and young fruit and cause the damage mentioned above.
TREATING PLUM POCKET
The spores of the fungi are spread through air and water from nearby infected trees and also from the affected tree itself. Once the fruit are initially affected there is no way to save them that year. Treatment is aimed at limiting the spread of the spores and at the same time spraying the tree before fruit buds form in early spring.
The first course of action is to remove and burn all affected fruit including those which have fallen to the ground. Take a close look at the tree and if you notice any unusually thick clusters of twigs growing from branches, prune them off because in all likelihood they are infected. As part of the normal pruning process remove any twigs and branches which look unhealthy.
A fungicide sprayed onto the tree will also limit damage very considerably. The best one we know of for Plum Pocket is Westland Plant Rescue Fungus Concentrate, the active ingredient is Difenoconazole. Spray the tree once in November and then again in March. An alternative is Bordeaux mixture sprayed at the same two times during the year.
WHITE POWDER ON PLUM TREE LEAVES
Plum trees often suffer from POWDERY MILDEW which is a fungal disease. The powder you see on the leaves are the spores of the fungus. We have a page dedicated especially to identifying and treating powdery mildew which can be found here. As far as plum trees are concerned the problem is most frequently caused by bad air circulation especially in the centre of the tree. Although plum trees withstand infrequent pruning better than most other fruit trees, this fungus often occurs where the foliage and branches are crowded.
Where the disease is left to progress secondary infections and pests may well attack the weakened tree. Aphids in particular (please use a magnifying glass to examine the leaves) are attracted to weakened trees and they may cause the mildew to turn sticky in places.
LEAVES HAVE LOTS OF LITTLE HOLES
The most likely cause of this problem is Shothole (also known as Coryneum Blight) and this section covers that disease. Similar holes can also be caused by Canker (damage to the bark will also be clearly present) and the Shothole Borer (stems and trunk also have holes in them).
The most obvious symptom is the appearance of lots of holes in the leaves. Initially they are brown circles of dying or dead tissue, as the leaf grows the brown circles fail to grow and eventually they fall off leaving the trademark round holes. These can join up over time leaving bigger holes in the leaves. Less obvious signs are brown marks around developing buds and / or grey spots on the fruit which may also include a resinous gum.
The disease is a fungal infection which thrives in damp and crowded conditions. It does respond to chemical treatment both in spring and autumn. In spring spray with an anti-fungal mix such as Westland Plant Rescue Fungus Concentrate. In autumn spray with Bordeaux Mixture. Large plum trees should still be sprayed as recommended even if you only reach lower parts of the tree. The fungus rarely affects the top of the tree, it is most vigorous lower down and in the crowded inner parts of tree canopy.
The fungus can also be controlled simply by reducing the number of affected leaves, buds and correct pruning especially of the lower parts of the centre of the tree. Firstly, remove all fallen leaves and twigs from around the base of the tree. If the area is water logged, try to provide good drainage to reduce humidity. Prune off all affected twigs which have infected buds.
Plum trees such as Victoria are more likely to be affected by Shothole because they tend to grow branches and foliage close together - perfect conditions for this fungus.
Plum trees which suffer from environmental stress such as hot or cold weather, fluctuating levels of moisture at the roots or similar conditions often produce plums which have small blobs of clear and hardened liquid on them, the picture below shows these blobs on plums.
There can be lots of them or just a few. As well as environmental conditions this can be caused by very localised insect damage or it can be the result of some other more serious pest or disease. The blobs themselves are not a pest or a disease but they are produced as a result of some other pest, disease or condition.
Cut an affected plum in half and look for signs of a pest, if none is found then the plum is still edible. If there are other signs then diagnose what has caused them rather than worry about blobs themselves, they are just a sign of another problem.
COMMENTS / QUESTIONS LEFT BY OUR READERS
|22 July 14||From: Tristan|
|I have two Victoria plum trees and the leaves have lots of little holes in and thousands of flies on the trees and the fruit is starting to fall off or rot. Also ground underneath seems to have lots of black mildew on. Any ideas? Thanks. Picture attached here.|
|21 July 14||From: Peter|
|I have a plum moth (plum sawfly?) infestation of my greengage in Cambridgeshire. Rather than "burning" the infected fruit as you suggest, I have placed a bucket of water next to the tree, and every time I pass the tree, I throw any infected fallen fruit into the water. The fruit immediately sink to the bottom, as do the white grubs themselves (they cannot swim - I tested this on one grub).|
|21 July 14||From: Jean C|
|My plum trees have holes all over the branches and tree trunks and there is a clear sticky sap coming from each hole, one tree looks dead and now the other tree has shrivelled up leaves and also hole all over the branches and trunk with sap coming from them as well. What is this and can it be treated.
FROM DAVE: Are you from the UK? I ask because that sounds very much like shot-hole borer and I wasn't aware that it commonly affected plum trees here.
|20 July 14||From: Caroline|
|Please could you help me identify what is the problem with my Victoria plum tree. I can’t decide if it may be
brown rot. Picture is attached
FROM DAVE: You've identified Brown Rot correctly, the small grey blobs on the fruit are a definite identifying sign. I have added a section on Brown Rot of plums in the article above for more identification details and what to do about this disease.
|13 July 14||From: Patricia|
|1st yr of setting plum tree. Lots of fruit but started to notice
clear jelly sticky stuff on plums which set hard, have been wiping off and destroying plums but still it comes - can you please tell me how to get rid? Thank you
FROM DAVE: Without a picture (send one using our email address if you want to) it's difficult to say for certain but it sounds like a normal reaction plums have when they suffer from environmental problems (water, heat, cold etc) or as a reaction to some other pest or disease. See the section "Clear Blobs of Hardened Resin / Jelly on Plums" above for more information.
|11 July 14||From: Robert Martin|
|All the plums that were on two of my three plum trees have gone none left on the trees none on the ground
FROM DAVE: If there is absolutely no trace of them then the only conclusion is that they have been eaten by a human who has then disposed of the stones. You don't mention if you have eaten them or possibly someone you know. If that's not the case then I fear that they have been stolen.
|6 July 14||From: Jim Wells|
|Plum tree about 12 years old for first time showing
sticky, white/grey powdery leaves though at present developing fruit seem unaffected. Any idea what may be and how to treat? Thanks, Jim
FROM DAVE: Sounds very like Powdery Mildew. I have added a section on this pest above entitled "White powder on Plum Tree Leaves".
|6 July 14||From: Jackie Rees|
|Victoria plum tree leaves turning brown around the edges also brown in the centre some have
small holes in the leaf. Your help please tree about 4years old with plenty of fruit.
FROM DAVE: There are many fungal diseases which can affect plum tree leaves and also environmental problems, especially water-logged soil, can also have the affect you describe although the holes are slightly more unusual.
ItIt may well be shot hole which causes brown spots in the leaves and some holes. I would spray a fungicide on the tree as a first course of action. There are several on the market, one well known one is Scotts Fungus Clear Ultra.
|26 June 14||From: PJ|
|My plum tree has come into leaf as normal, but now nearly all the leaves look withered and are dying, but there is a lot of unripe fruit forming normally. No sign of any disease that I can see, but it looks very poorly. Could it be old age? It\'s probably about 20 years old at least
FROM DAVE: I doubt very much that age is the problem, plum trees normally live a lot longer than 20 years. If there are no signs of aphids (use a magnifying glass to look at the underside of leaves to be 100% sure) or other pests / diseases then the problem sounds environmental. Has the area flooded last winter / spring? Has it been pruned regularly? Anything else changed in the last year or so?
|01 June 14||From: Walter Awlson|
|I have a mature Victoria Plum tree which is badly affected with
"pocket plum". Following advice to remove branches with affected fruit, there is very little left and obviously no crop this year. Is there any treatment which will help save this tree and prevent a recurrence?
FROM DAVE: Plum pocket was previously very rare in the UK but over the last three years it is becoming more widespread. I have included a new section above in the main article on this pest to describe its lifecycle, identification and treatment.
|Date: 23 May 14||From: Irene G|
|My mature Victoria plum tree has failed to come into leaf this year. There was early evidence of small buds but they have failed to open. There are no visible signs of canker or damage to the the outside of the tree. The only change to its environment was the stacking of logs from a tree we cut down last autumn approx 2m from the tree base. Could this have damaged roots? Some twigs can be snapped but others still appear to have sap. Any help/suggestions welcomed.
ANSWER: A difficult one to diagnose because the first possibility is environmental. Too cold, too wet or (most unlikely) too dry. That pile of wood you mention may be causing water to remain in the ground longer than it normally would and after all the wet weather we have had that could be the problem.
Plum trees are notorious for changing their growth habits from one year to the next. I would suggest waiting until next year to see what happens especially because the tree is obviously alive with no external signs of damage,
|Date: 19 May 14||From: Brian H|
|I have pea sized black blisters on the underside of the branches
of my yellow plum tree. What are they and how can I treat it. Pictures attached.
ANSWER: These are scale insects, almost certainly Lecanium Scales. I have added a section in main article above on how to identify and treat them. Thanks for the pictures which greatly help to identify the problem.