Ask the Plant and Pest Professor

by Ellen Nibali

QUESTION: I have about 30 azaleas in my garden in full sun and shade. Soil is clay with many layers of mulch. Some azaleas are dying, and I don't know why. They were not watered well last summer due to drought and water restrictions. I recently sprayed insecticides and fertilizer just in case. Leaves are browning and branches turning black. We have white oak tree whose leaves, we believe, acidify the soil.
ANSWER: Many azaleas did not survive the droughts over the last 3 out of 4 years, especially those in full sun. Azaleas prefer moist acidic woodland soil and filtered shade. They have shallow root systems. Your white oaks also compete with the azaleas for water. If your mulch is over 2 or 3 inches it may have been a barrier to the little rain we did receive. Drought and drying winter winds both weaken plants and make them more susceptible to problems. If your azaleas winter injury is sunscald, they may recover. If the branches have blackened spots on the bark, also known as cankers, or are dropping dead branches, they may have a fungal disease. In any case, it is crucial to find the exact problem before using pesticides or fertilizers, as these can aggravate plant injury. To further pinpoint the symptoms, use the diagnostic chart on our publication, IPM: Azaleas and Rhododendrons. Read it online or call us and order. Also, view the color photos in the Plant Diagnostics section of our website. Meanwhile, prune out your azaleas dead wood and consider having your soil tested. You can order a soil test from us either online or by calling.

QUESTION: Our fescue lawn is infested with moss. Last years soil test recommended no lime. We have shade, compacted clay, good drainage. We seeded last fall, and just applied a starter fertilizer. Have had this problem for the last 30 years. How do we get rid of it?
ANSWER: Moss is present in lawns for five primary reasons: compacted soil, too much shade, poor drainage, low soil fertility, and acidic soil. To eliminate the moss you need to determine why it is present in your yard. Sounds like your pH is high enough and you have good drainage. Fall is the best time to use a plug aerator to improve the soil compaction. Fine fescue is best for shade, however if your lawn has less than 3-4 hours of sunlight a day, you may not be able to grow good turf unless you can lessen the shade. Keep your turf thick and actively growing by utilizing proper cultural practices. These include fertilizing at the proper time (fall is best) and mowing high. For additional information, read, HG100 Moss Control in Home Lawns.

QUESTION: We want to plant English ivy as a ground cover but do not want it to encroach on our neighbors' yards. Do you have a suggestion on how we can keep it within our property?
ANSWER: Usually English ivy is not a recommended ground cover because it is so hard to control. It is now on many lists of exotic invasive plants that invade native or park areas. The only situation in which it is appropriate is away from native or wild areas, in a site where it can be mowed around its entire perimeter and prevented from climbing trees and flowering (which produces seeds.) Alternatives for English ivy include epimedium, St. John's wort, periwinkle (keep this away from woodlands, too), pachysandra, creeping phlox, creeping thyme, liriope, plus many others.

QUESTION: Please advise which fruit tree is best suited for Maryland.
ANSWER: Many fruit trees will grow well in Maryland. Apples and peaches tend to have the most pest problems. Fig, Japanese persimmon, plum, tart cherry and Asian epar can be grown organically in many cases. Lists of preferred varieties of fruit trees for Maryland gardens is available on our website or by calling HGIC. Also consider growing small fruits such as blueberries, blackberries, raspberries. They provide high yields for the least amount of effort, and they rarely require pesticide sprays while almost all fruit trees do.

QUESTION:Last year I used the red colored mulch. Are there differences in effectiveness? (Keeping deer and insects at bay, for instance.) Or is the benefit just color?
ANSWER: Using colored mulch is a matter of aesthetics, there are no other benefits. The wood chips are dyed to enhance their ornamental value. There are no types of mulch that serve as a deer repellent. If insects are a concern, do not use more than the recommended 2-3 inches of mulch around your plants and keep mulch 12-18 inches from the foundation of your house.

QUESTION: I noticed a sticky substance on my floor under a fern I have had for years. There is a white substance on some of the fronds and a brown scale. Now I see ants near and on the fern. This is a very large fern, and I don't want to lose it. I detected the same stickiness on some ivy, and I washed it with soap and water.
ANSWER: Ferns can be susceptible to two pests - scale insects and mealybugs. They are sucking insects. When they feed they excrete a sticky substance called "honeydew". The ants are attracted to the honeydew as a food source and will protect the sucking insects to keep up the flow. Scale insects are likely to occur along the veins on the underside of the fronds. You can apply denatured alcohol to the scales with a small paint brush then wipe off scale, or use a labeled indoor insecticide. However, it is difficult to rid plants of scale. Sometimes the only solution is to dispose of badly infested plants before the scale spreads to other houseplants. It sounds like it is already on your ivy.
        Mealybugs (insects coated with a white waxy substance) are found on new growth and can be treated in the same way. Use alcohol sparingly because too much of it can damage young growth. Ferns are very susceptible to insecticide injury. Horticultural oil is a control for scale insects and mealybugs, but read label directions carefully to see whether it is labeled for use on ferns.

”Ask the Plant and Pest Professor” is compiled from questions sent to the website of the Home and Garden Information Center (HGIC), part of Maryland Cooperative Extension, an educational outreach of the University of Maryland. To ask a home gardening or pest control question or find other help, go to Or phone HGIC at 1-800-342-2507, Monday through Friday, 8 a.m. to 1 p.m. Any questions? E-mail or call Ellen Nibali at 1-800-342-2507.

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This story was published on May 7, 2003.