August 8, 2014 at 1:00 am

Gardening

Spruce trees under siege in lower Michigan

Weather over the past seven years has caused once healthy blue spruce trees to have needle cast and branch dieback. (Todd McInturf / The Detroit News)

“What’s wrong with my blue spruce?” is the lament of homeowners throughout Michigan. The U.S. Forest Service Christmas Tree Pest Manual lists 20 pest problems on blue spruce, and that’s just for starters.

According to research by the Plant Pathology Department at Michigan State University, all species of spruce trees, including the beloved Colorado blue, are experiencing a decline throughout Michigan’s lower peninsula. According to Michigan State University’s records, the needle cast and branch dieback that began about seven years ago have reached epidemic proportions.

The reasons for spruce decline include weather and cultural conditions that also take their toll. Too much spring rain and extended summer drought are part of the equation. Poor siting and improper planting are other reasons. Homeowners love to plant these beauties in groups, which works when they are young. But as the trees mature, they begin to cast shadows on their neighbors, and the shaded areas die out. Crowded trees get limited air circulation, making them vulnerable to disease.

The canker diseases are the most problematic. Research shows fungicides are generally ineffective, so the only treatment is removal of infected branches along with improved circulation and tree vigor.

Limbing too far up the trunk makes these shallow-rooted trees vulnerable to “tipping” should they be buffeted by strong winds.

Dr. Bert Gregg, Ph.D., an associate professor at the Michigan State University Department of Horticulture and Forestry, is currently researching urban tree selection in a changing climate. Here are some of the selections he recommends to replace an ailing blue spruce.

■Concolor fir (Abies concolor) is an attractive medium to large evergreen with 1½- to 2½-inch needles which vary from green to almost silver–blue in color. Adaptable to alkaline soil and hot, dry weather, it grows from 30 to 50 feet in height. Recommend cultivars are ‘Blue Cloak’ and ‘Candicans.’

■Alaska cypress (Chaemacyparis nootkatensis) is a fast-growing specimen with lovely, weeping branches and is hardy to Zone 4. It will climb 30 to 45 feet in height, but care must be taken to keep its feet in moist soil. ‘Green Arrow’ and ‘Strict Weeping’ are cultivars chosen for their extremely narrow, upright form.

■Serbian spruce (Picea omorika) grows 1 to 3 feet annually into a tall, upright, sweeping form. Hardy to Zone 4, this large tree is graced with blue green needles and silver undersides.

Others to consider are the Swiss stone pine (Picea cembra), Korean pine (Pinus koraiensis), Baldcypress (Toxodium distichum) and Dawn redwood (Metasequoia glyptostroboides).

Nancy Szerlag is a master gardener and a Metro Detroit freelance writer. Her column appears Fridays in Homestyle. To ask her a question, go to Yardener.com and click on Ask Nancy. You can also read her previous columns at detroitnews.com/homestyle.