Peony
Blight
Q: Last summer my neighbor
told me the black spots on my peony were a blight,
although my peonies bloomed nicely. What can I
do about this?
A: Your peonies probably have a fungal disease,
a common problem. The causes are wet summers with
cool damp nights, too much shade, poorly drained
soil, or a lack of air circulation. While your
neighbor diagnosed your problem as peony blight,
which is caused by an air-borne botrytis fungus,
the black spots indicate the more common phytophthora
blight, according to Walter Schmidtke, nursery
manager at Pesche's Garden Center in DesPlaines.
Early in the spring, young emerging shoots may
suddenly wilt and fall over, turn black and show
masses of gray-brown botrytis spores. If nothing
is done, these spores are carried to developing
buds, which turn black.
Black spots on foliage, leaves turning red in
summer, and black stripes on the stalk indicate
phytophthora. "Plants with these conditions
won't have as much zest" said Schmidtke.
The best protection against recurrence of either
blight is good sanitation. In fall, it is important
to cut down and throw away all peony foliage,
cutting stalks just below the surface of the ground.
If this doesn"t work and you resort to chemicals,
the treatment is the same for both diseases. As
soon as the shoots emerge in spring, begin spraying
with Mancozeb, a copper sulphate solution, and
repeat every 7-10 days until buds form, according
to University of Illinois Extension. Spray the
whole soil area for overwintering spores. In early
summer you can spray plants with Daconil, a general
purpose fungicide. Cut away any diseased foliage
at once. Back to top
Rose of Sharon - Botrytis Blight
Q. I have two 3-year-old rose of Sharon plants, about 20 feet apart. One blooms every year. The other plant forms about 100 buds and looks healthy, but it has not bloomed in the last two years. The buds are solidly closed and look as if they are rotting from the inside out. There does not seem to be any sign of insects on the plant. What is this problem?
A. From the description it sounds like your plant is infected with botrytis blight, a fungus disease that attacks buds before they open, according to Jim Schuster, extension educator, horticulture, University of Illinois. Your plant needs to be treated with
a fungicide early in the season. Remove all diseased portions of the plant and any residue on the ground, as the fungus lives over winter in
discarded material. Back to top
Lilac - Powdery Mildew
Q. My lilac had a grayish blight on the leaves this summer. What caused this and how can I prevent it?
A. Your lilac had powdery mildew,
a common fungal disease. It occurs
in late summer in humid weather, especially if your plant is located in
a damp, shady area. While unsightly,
it does not damage the plant since it only affects the outermost leaf cell layer. If it really bothers you, spray the leaves with a sulfur fungicide early in the season. If mildew appears late in the season, spray again.
Newer varieties of lilac are more disease resistant than the common lilac. Improving air circulation by pruning out any dead branches will also help to reduce mildew, advises Joan Barczak, owner of Blumen Gardens, Sycamore. Back to top
