I have either leaf spot or leaf rust on my blueberry plants that just...
I have either leaf spot or leaf rust on my blueberry plants that just occurred in the last couple of weeks but is spreading rapidly with some leaves completely covered. I sprayed an horticulture oil on them 5 days ago with no avail. Should I use a fungicide and can any work? I already have Immunocide in my possession.
Beaufort County South Carolina
Thanks for including a picture! The black, sooty appearance of the leaf makes me suspect scale insects. I can also see a few small, immature scale insects on the upper surface of the leaf, so they are definitely present on the bush. For information on control and to see pictures of scale insects on blueberry, see:
Leaf spots or rust may also be present, but I would need to see more pictures to verify. Sprays at this time of year are not effective against leaf diseases. Leaf spot sprays are most effective when fungicides are used prior to the onset of disease, in June and July. Oil sprays are not effective against leaf diseases but may be useful as a delayed dormant spray in February to help control scale insects.
Leaf spot diseases on blueberry cause the leaves to fall off prematurely in late summer, so if bushes still have most of their leaves attached at this time of year (November), then leaf spots are not a big problem at your site and I would not worry about applying fungicides.