I planted five holly bushes last spring. I believe the variety is Blue Prince. They are spaced about a meter apart. Now many of the leaves are developing tiny, black pin-prick sized spots, after which they turn yellow and drop off. I dispose of the leaves that have dropped, and I’ve sprayed with a fungicide this spring, but the bushes are loosing leaves quickly. What should I do ?
From your description of the spots on the holly leaves, I believe we can eliminate fungal leaf spots, or blight, which affect much larger areas of the leaves. Further, you have already initiated treatment with a fungicide on your holly plants, with no evident success. Also, your plants are spaced far enough apart that they would not seem to be preventing good air circulation.
So, now, I would suggest that the tiny dots of black are the result of aphids: they suck sap from the leaves, and produce a waste product called “honey dew”. This sticks to the leaves, and promotes the growth of a black mould, hence black dots, which then result in leaves yellowing and dropping.
Steps to eliminate aphids on holly plants can begin with cultural controls that are not complicated: keep your holly plants healthy and strong, so they can withstand any insect infestations. Then we recommend organic controls. Spraying water from a hose, or a water spritzer, can knock off most aphids, aided by wiping off the aphids by hand.
Next, growing nearby plants that attract beneficial insects that feed on aphids, such as ladybugs, is a great biological control. Ladybugs are attracted to milkweed and cosmos, to name a few. Finally, certain plants themselves, growing nearby, help deter aphids: coriander, chives, painted daisy and cosmos.
If infestation on a holly bush is severe enough, one of the better solutions for a holly is horticultural oil, to be sprayed on the top and undersides of the leaves, which will smother both insects and eggs.
May your hollies bear many berries for the season !