Spraying away dogwood fungus

Garden Q&A

November 17, 1996

I have two flowering dogwoods that looked droopy and peaked this summer. The leaves had a white powder on them. Should I be worried? Is the problem wet weather?

The problem is a fungal disease called powdery mildew, which is more widespread during wet growing seasons. This is not a devastating disease, like dogwood anthracnose, but should be controlled when symptoms are severe. If symptoms reappear next year, spray foliage thoroughly with a horticultural oil that is registered for use against powdery mildew. Follow the growing season recommendation on the label. Don't apply oil sprays when the temperature is above 85 degrees or on very humid days.

Varieties of flowering dogwood (Cornus florida) resistant to powdery mildew include Cherokee Brave, Pink, Sweet Water Red and Wonderberry. Almost all Cornus kousa varieties are resistant.

My neighbor told me that I shouldn't compost my oak leaves because they are too acidic. Is this so? Should I add lime to my compost pile?

Oak leaves are acidic when they fall from the tree (pH around 4.5), but finished compost made entirely from oak leaves will have a pH of around 7.0 (neutral). Uncomposted oak leaves used a mulch may cause a small drop in soil pH. Don't add lime to your compost pile. It causes nitrogen in the pile to be driven off as ammonia gas and inhibits the tiny fungal and bacterial decomposers.

A neighbor told me that you can buy worms that will eat kitchen garbage year-round inside your home. It sounds weird but I'm curious. How do you get started?

bTC Indoor composting with redworms, also called vermicomposting, is becoming popular with the gardening public. Redworms (Eisenia foetida) are especially suited to the task because they -- live and reproduce in confinement and eat their weight in kitchen scraps each day. The end result is a rich, composted plant food. All you need to get started is a plastic or wooden box with plenty of holes for air circulation, moistened newspaper strips for bedding, 1 to 2 pounds of redworms and the household kitchen scraps -- coffee grounds, fruit and vegetable cores and peels. The worms will reside comfortably in a kitchen closet or basement and will not crawl out unless they are very unhappy (no food or too wet). For information on suppliers of redworms and ready-made vermin-composting kits, request the University of Maryland fact sheet "Indoor Redworm Composting," by calling the Home and Garden Information Center at (800) 342-2507.

Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions or if you have questions of your own, call the center's hot line at (800) 342-2507.


To reduce the incidence of fungal leaf diseases such as anthracnose, rake up and remove the fallen leaves from shade trees that were infected over the growing season. Where possible, compost these leaves at high temperatures.

Clean the plant debris and soil from garden tools, sand off rusty spots and rub oil on the metal parts. Wooden handles can be winterized with an application of linseed oil.

If your blueberries grew poorly this past season, have a soil test done and amend your soil accordingly. Soil pH should be between 4.5 and 5.2 for good growth. Incorporate 1.5 pounds of iron sulfate per 100 square feet of growing area to drop your soil pH by half a unit. For example, you would need to incorporate 6 pounds of iron sulfate per 100 square feet of growing area to drop the pH from 6.5 to 4.5.

Pub Date: 11/17/96

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