This tree was planted last year but failed to flower, which is not surprising as it was late June. It suffered black fly on some stems, cleared with recommended spray, but in August of this year, leaves have a mild case of a fern-looking pollen-like covering on the underside of the leaves with a yellowing on the top side. It has continued to attack most of the leaves now but I cannot find out what it is. Can you help?
This sounds like some form of rust. This article has more information: https://plantdiseasehandbook.tamu.edu/food-crops/fruit-crops/plum/
You might want to check the culture of your tree, to make sure there is not some problem there that is weakening your tree: https://www.gardeningknowhow.com/edible/fruits/plum/growing-plum-trees.htm
We have a 7 year old Victoria plum tree which has never fruited very well. Last year what fruit ripened was marked and scarred. This year it appeared to be budding prolifically but some leaves have got holes in them without evidence of 'bugs' and the end of the new growth are drying and curling. Also, the buds are all going bright yellow and falling off. Any advice would be appreciated.
It does sound like aphid damage to your tree and fruit.
Neem Oil is a good treatment.
https://www.gardeningknowhow.com/edible/fruits/plum/control-leaf-curl-plum-aphids.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Leaves on tree look as though they are being attacked by caterpillars, although I have not seen any. What can I do and will this stop it fruiting?
Products containing Bacillus thuringiensis (like Safer or Bonide) will help and are readily available at most garden centers and plant retailers. Here is more information on getting rid of caterpillars: https://www.gardeningknowhow.com/plant-problems/pests/insects/prevent-caterpillars.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/using-bacillus-thuringiensis.htm
We have a Victoria plum tree. It's 6 years old. We have the 1st plums forming but a lot are dropping off, and they are very small. Why are my Victoria plums falling off before they are ripe? The tree is only young and is suitable for a pot.
Heavy fruit set could cause the small plums to drop off. You can select some of the fruit to remove giving the tree the ability to send more energy to less fruit.
https://www.gardeningknowhow.com/edible/fruits/plum/growing-plum-trees.htm
As my Victoria plums are ripening, they are splitting. They are small splits and then they fall off the tree.
Plum fruit split is normally the result of erratic watering. The splits in the skin tend to happen when a hot dry spell rain is broken by plenty of rain. The moisture causes the fruit to swell too quickly and the skins split. The "cure" is simply to make sure there is a consistent supply of moisture to your plum trees.
We have an 8 year old Victoria plum tree. Last year we got very few fruits but were not particularly bothered but this year all of the fruit has become rotten on the branches and we have only managed to get 4 edible plums. Is the tree diseased and can we fix it?
It could be brown rot. This article should help: https://www.gardeningknowhow.com/edible/fruits/peach/brown-rot-fungus.htm
For additional plum tree issues, this article will help: https://www.gardeningknowhow.com/edible/fruits/plum/plum-tree-diseases.htm
3-year old Victoria plum tree with only 2 plums. All the leaves are yellow and wilted. Looks very sick.
Plum trees began to bear fruit after they are 3 so your tree is just reaching this age.
There can be a few reasons for the yellowing leaves, including watering issues, insects or disease.
Inspect the plant carefully for insect damage.
Here are some links for you.
https://www.gardeningknowhow.com/edible/fruits/plum/plum-trees-not-fruiting.htm
https://www.gardeningknowhow.com/edible/fruits/plum/plum-tree-diseases.htm
https://www.gardeningknowhow.com/edible/fruits/plum/plum-tree-pruning.htm