victoria plum tree with leaf fungi (brown)
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