I have 3 x standard roses and 5 x other variety (unknown), they have all been very stunned in growth this season with 2 looking almost dead. There are red dots on leaves of all the roses - I think it's a magnesium deficiency Any ideas on how I can get rid of the red dots and why 2 out of 8 are not growing?
It looks like Leaf or Black spot, which is a fungal infection. Roses are very prone to fungal diseases especially in humid areas. You can spray the leaves with a fungicide. However I prefer to use Rose Shield which it is an all-in one insecticide, fungicide and miticide controlling insects as well as fungal infections.