| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Ascochyta Blight |
In the spring, current years shoots and flower
stalks are girdled, wilt, and brown. The base of the dead area
is tan to gray and shrivelled. In wet weather, dark gray pimple-like
fungal fruiting structures dot the dead tissue. In summer and
autumn, olive-green round leaf spots turn tan and have indefinite
edges. Fungal fruiting structures dot the upper surface of the
spots. |
Ascochyta syringae |
Prune infected tissue. Avoid overhead irrigation.
Apply thiophanate methyl to protect healthy shoots. |
| Bacterial Blight |
Leaves turn completely brown to black and remain
attached to the branch. Shoots are girdled and killed. Flower
buds are blackened while flower clusters become limp and brown.
See shoot blight below. |
Pseudomonas syringae |
Avoid overhead watering in the spring. Prune
infected branches cutting well below the diseased tissue. Disinfest
the pruning shears between cuts. |
| Powdery Mildew |
Dry white fungal growth develops on the surface
of leaves. Leaves become distorted. |
Microsphaera syringae |
Apply an antitranspirant at 30-day intervals
before mildew appears, usually June, July, and August 15. Reapply
the material if mildew appears before 30 days have elapsed.
Or, apply paraffinic oil, myclobutanil, thiophanate methyl +
mancozeb, triadimefon, or triforine. |
| Shoot Blight |
Shoots are killed extensively, up to 4-5 feet,
and turn very black. Root sprouts at the base of the plant are
killed and blackened. See bacterial blight above. |
Phytophthora cactorum |
Remove the infected plant and do not replace
it with plants susceptible to Phytophthora.
Avoid overhead watering of healthy plants. |
| Witches' Brooms |
Short, thin twigs and branches originating from
one area of the stem form dense clusters. Leaves may be distorted,
small, and yellow. Twigs forming the brooms are abnormally upright
and oftern retain green leaves too long in the autumn and die
back in winter. |
Phytoplasm |
Prune affected branches. Remove severely infected
plants. |
