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Banish Black Dust

In summer, sooty mold coats plants, cars and outdoor surfaces

Every summer, home gardeners seek cures from a black dust-like substance that clings to everything outdoors, including plants. That dusty grime that you can’t seem to wipe away is called sooty mold.

Sooty mold is a saprophytic fungus that feeds off sugary substances released by such insects as aphids and scale feeding on plants. If aphids and scale insects happen to be feeding on tall trees, they’ll excrete a sugary substance called frass. The frass drifts down and sticks to whatever is beneath.

The spores of sooty mold fungus multiply all the faster under hot and humid conditions, establishing more and more colonies, especially among an abundant supply of frass.

Sooty mold can be controlled by spraying the plants with a fungicide called ferbam — which is also black — and will not make things look any better.

The best and most efficient control for sooty mold is to control the insects that create the frass. For aphids, consider using insecticidal soap. Weekly applications will generally provide adequate control. If the aphids are feeding on a large maple, tulip poplar or oak, you may need to contact a commercial company to spray the tree, or consider using a systemic insecticide added to the soil beneath the tree for the roots to absorb.

Control scale insects with horticultural oils. Horticultural oils are safe and used by organic gardeners to control spider mites and scale insects.

They are extremely effective and may require only one or two applications.

Moving a Japanese Maple

Q We have lived in our Annapolis home for 10 years, and the Japanese maple that previous owners planted in our small front yard is now too close to the house and crowding out a very nice dogwood.

The maple is spindly, not six inches in diameter at the ground, about 12 feet tall and with a canopy probably not more than 10 feet in diameter.

I’d prefer not to cut the tree down. Is this maple too large to dig up and transplant, and if not, how and when should it be done?

–Alex Knoll, Annapolis

J apanese maples are not hard to move because they have a very fibrous root system. The root ball size is determined by the trunk diameter, measured six inches above the ground. For every inch in diameter, the root ball increases by eight to 10 inches. For instance if the trunk is four inches in diameter, the root ball should be 32 to 40 inches in diameter.

The tree can be dug any time after the first flush of growth is complete but before the second flush of growing begins. If the second flush of growth has started, wait until the tree has finished flushing before digging.

After determining the ball size, outline the diameter of the root ball with the trunk in the center. Using a shovel with a sharp edge, dig straight down approximately 12 inches. Next dig a trench eight to 10 inches wide around the outside edge of the root ball; this should not damage the walls of the root ball. Undercut the root ball until you can begin rocking the tree and root ball.

If you are moving the tree a short distance, you can slip a heavy canvass under the root ball and dig a ramp to pull it out of the hole. A root ball 40 inches in diameter and at least 12 inches thick will weigh 200 to 250 pounds.

Be sure the soil is moist when you dig, and do not let it dry out.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.

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