The symptoms are dead material between the leaf veins, along the
leaf edges or dead tips of leaves. There are also times when the
disease affects buds and twigs. In the leaf stage, the disease
only affects leaves currently out. If the leaf damage results in
enough dropped leaves, the tree will shoot another set within
four to six weeks. All we're out is the energy the tree spent in
pushing out another set of leaves. Of course, we also had a
freeze that caused the loss of leaves on many trees. What I'm
getting at is that trees have spent quite a bit of energy
already this year. We need to do what we can to replace
nutrients and keep moisture available.
Moisture will be needed
to keep those affected trees in a vigorous growing condition.
Usual watering rates are an inch a week, and rainfall can supply
part or all of that. Fertilizer applied to lawn area or trees is
the other part of the equation. Fertilizer should be applied at
the lawn rate (supply 1 pound each of nitrogen, phosphorus and
potassium per 1,000 square feet of drip area) if you haven't
fertilized the lawn area around the trees. This would translate
to about 10 pounds of 10-10-10 fertilizer or 8 pounds of
12-12-12 or 13-13-13 per 1,000 square feet.
Other leaf diseases are also quite evident. One the more
common ones is apple scab. This disease affects apples and crab
apples in much the same way as anthracnose does the shade trees.
It starts as spots on leaves between the veins of the leaves and
ends with leaves dropping at a rapid rate. This is the reason
for so many "naked" crab apple trees late in the summer.
Traditional spray programs for production apples (used on the
apples or crab apples) should prevent the problem. Samples of
apple scab have been coming in for a week now, so expect some
acceleration of the disease on susceptible varieties.
[to top of second column]
It is time to take action against the notorious oystershell scale
because the eggs are now hatching into young crawlers that are
extremely susceptible to insecticide applications. However, as the
scales mature later in the season, they are more difficult to
control because they form an impenetrable protective covering.
Oystershell scale has a wide host range, including ash, birch,
dogwood, elm, hemlock, maple, poplar, privet, walnut and willow.
Eggs hatch into creamy white to brown crawlers that are active
from May through June. The crawlers locate a place to settle and
then use their piercing-sucking mouthparts to remove plant fluids,
which causes leaf yellowing, plant stunting and possibly death.
Branches or twigs totally encrusted with oystershell scale
Insecticides recommended for managing oystershell scale include
acephate (Orthene), bifenthrin, carbaryl (Sevin), malathion,
insecticidal soap and horticultural (summer) oil. All these
insecticides should be applied when the crawlers are most active,
which increases their overall effectiveness in controlling
oystershell scale populations. Repeat applications may be needed 10
to 12 days later, as the eggs don't all hatch at the same time.
Lilacs and maples should also have a repeat spray in early August.
Believe it or not, it's time to think of fall gardens. Summer
squash seedings should be wrapped up, potatoes seeded and New
Zealand spinach seeded.
Some tomatoes are also experiencing some disease problems. The
main ones are the leaf spot fungi such as Septoria. Protective
sprays of a fungicide will slow the progression to the new leaves.
Just make sure to read the label on the product for the
days-to-harvest restrictions. Also make sure your tomatoes are
mulched, as conditions are ideal for blossom end rot, caused by
uneven moisture conditions.
University of Illinois Extension, Logan County]