If magnolia leaves turn black, problem could be scale insect

Backyard Q&A

August 14, 2005|By Jon Traunfeld and Ellen Nibali | Jon Traunfeld and Ellen Nibali,Special to the Sun

For five years, our pink-flowered magnolia had large black ants on it. Now it also has black and white bees. The leaves are turning black. It gets full sun. Any suggestions?

It's likely that your magnolia tree suffers from a scale insect. Magnolias are susceptible to three types. Look for bumps along the 1- to 2-year-old twigs of the tree. Scale insects excrete a sweet substance called honeydew. Honeydew provides an ideal substrate for black sooty mold to develop. Usually foliage blackened by sooty mold is the homeowner's first clue that there is a scale problem. Honeydew also attracts other insects who use it as a food source -- hence the ants and wasps. They are not a concern.

Branches heavily infested with scale can be pruned out, or a horticultural oil can be sprayed during late fall, late winter or early spring, when the tree is dormant. Spraying in August and September is ineffective.

My 'Blue Lake' bush beans get small round brown abscesses on the beans -- more on the lower beans and older plants. The problem appears after I have been picking the beans for a week or so. (I do successive plantings). A few beans have warts in addition to abscesses. What can I do?

The fungal disease anthracnose produces sunken black lesions on pods. Under wet, humid conditions, these can be covered with salmon-colored spores. The fungus overwinters in seeds, soil and plant residue.

You should avoid overcrowding plants to promote good air circulation. Avoid contact between soil and pods by mulching lightly and not working near the plants when they are wet. Remove infected beans. Clean up debris at end of season.

The occasional wart is probably a growth irregularity caused by abrupt temperature or moisture change, or it could be a genetic defect in a particular plant. Nothing to worry about.

I am positive I saw a bat fly into a tiny space between the bricks and the roof of my house this morning. What should I do?

As long as the bat is outside your house, there is no need for concern. Bats are beneficial creatures who eat volumes of insects. (They're a first line of defense against mosquitoes, especially the nasty, newly imported tiger mosquito.) Check your attic to be sure the bat has not gotten into the house. If so, simply wait until he flies out at night and seal up the entrance he is using.

Bats are a protected species, so if there are baby bats in the house, you must wait until fall when they are mature before excluding the family. A wildlife control service, listed in the phone book, can install a device over the entrance hole that allows the bats to fly out but not back in. Our bat publication is available by calling us.

Jon Traunfeld, regional specialist, and Ellen Nibali, horticulture consultant, work at the University of Maryland Cooperative Extension's Home and Garden Information Center. The center offers Maryland residents free gardening information and answers to plant and pest questions. Call its hot line at 800-342-2507 (Monday through Friday, 8 a.m.-1 p.m.) or e-mail questions to www.hgic.umd.edu. (You can also download or order publications and diagnose plant problems online.)

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