I noticed my honeysuckle, which is intertwined
to look like a topiary bush with the greens and flower all bunched
up at the top, to have yellowing of the leaves and drop off. Why
are the leaves yellowing? It smells lovely and is green on the
outside, but if you look under the canopy you can see many yellow
leaves. Is it a disease? Should I use a fungicide?
There are a few possibilities. It might be a kind of leaf blight, as
described by Iowa State University Extension.
Leaf blight is a fungal problem, but the control methods described above are not
nontoxic, so you may want to look for a safer fungicide (example here), and also
try to prevent the ideal conditions for fungus. Avoid wetting the leaves
of the plant, and make sure there is good air circulation around the
plant (by siting it properly, and by pruning to keep the plant’s shape
open).
Yellowed leaves could also be caused by scale, which is an insect. Do you
see small bumps on the leaves and stems? If so, here are recommendations
from The Organic Gardener’s Handbook of Natural Insect and Disease
Control edited by Barbara Ellis (Rodale, 1996):
“Minor infestations can be controlled by scraping the insects off the
plant with your fingernail, and by pruning out the most infested parts of
the plant. You can also use a soft brush and soapy water to scrub scales
off the stems, or you can apply dormant oil to the trunk and stems of the
plant just before growth begins next spring, and use superior oil during
the growing season.”
Because I’m not certain which type of problem your honeysuckle may have,
you should bring a sample to a Master Gardener Clinic.