Ash
Anthracnose (fungus)
Large,
irregular brown spots mostly along leaf margins. In rainy seasons, when the disease
is most severe, leaves drop prematurely. Collect and remove fallen leaves. Usually,
disease is not serious enough for fungicidal control, except in unusually wet
seasons or locations with severely restricted air circulation. Use chlorothalonil,
fixed copper compounds, mancozeb (some brands of mancozeb are labeled for white
ash only), quaternary ammonium compounds, or thiophanate-methyl.
- Resistant or tolerant varieties
Green ash is relatively resistant.
Decline (various
causes)
Trees
lose large branches over several years and may die. No one cause has been identified.
It is probably a complex of insect, disease and environmental problems, such as
moisture stress and freeze injury. A close association between ash decline and
ash yellows, caused by a phytoplasma, has been reported. Follow standard horticultural
practices for pruning, fertilizing and watering. If specific insect or disease
problems are recognized, appropriately treat each specific problem.
Flower gall (mite)
Male flower clusters become enlarged, distorted and woody. May persist on tree one or more years.
Does not affect tree vigor.
Leaf scorch
(various causes)
Leaf margins brown and dry up when water uptake is less than water need. May
be due to drought, a xylem limited bac terium, Verticillium wilt or root diseases
associated with decline. Mycophaerella leaf spot may resemble this.
Water deeply during dry periods.
Mycosphaerella
leaf spot (fungus)
Irregular browning and blotches usually occurring in the summer or fall.
In fall, clean up fallen leaves.
Plant bug (insect)
Leaves may be mottled, stippled, distorted or have irregular brown spots.
Black excrement may appear on either surface. The feeding of these insects has
little effect on plant vigor.
Verticillium
wilt (fungus)
Leaf scorch, dieback of branches and long-term decline. No fungicidal control
is possible. Remove severely affected plants. Replant only with resistant species.
Yellows (phytoplasma)
Decline, premature death, witch's broom, suckering from limbs and trunk and
leaves and twigs stunted are increased evidence of freeze injury. Remove affected
trees.
- Resistant or tolerant varieties
Both green and white ash are affected, but green ash often tolerates
infecton without progressive decline.
Update6/5/09