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Trees may need assistance

Anthracnose continues

By John Fulton          Send a link to a friend

[June 11, 2007]  A lot has happened in a week with our trees. The maples continue to show increasing leaf drop. Sycamores have been hit with a vengeance, and leaves have been falling like rain for the last week. Other good-quality hardwoods, such as ash, are also showing symptoms.

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 damage to leaves results in enough dropped leaves, the tree will shoot another set within four to six weeks. All they'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.

Anthracnose is usually the first leaf spot fungus to affect trees each spring. That means the others can't be far behind. 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.

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Oystershell scale

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 eventually die.

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 the 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.

[Text from file received from John Fulton, University of Illinois Extension, Logan County Unit]


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