In the Yard for Jan. 18, 2013

Photo provided by the LSU AgCenter -- Drought, disease, increasing summer temperatures and borers contribute to the decline of once plentiful Cornus florida (dogwood). Show caption
Photo provided by the LSU AgCenter -- Drought, disease, increasing summer temperatures and borers contribute to the decline of once plentiful Cornus florida (dogwood).

Once a ubiquitous understory tree in our woods and home landscapes, the great dogwoods (Cornus florida) have been in decline in recent years, said Allen Owings, LSU AgCenter horticulturist at the Hammond Research Center.

For more on Cornus florida’s decline and suggested alternative trees, go to http://www.lsuagcenter.com/hammond or learn more on Facebook.

In brief, we’re seeing fewer dogwoods in the wild and nursery growers are producing limited numbers of the trees, Owings said.

Dogwoods in the South have been declining and dying at alarming rates over the past 20 years, he said. Diseases such as dogwood anthracnose and powdery mildew have taken a toll. Some entomologists feel dogwood borer insects have been partially to blame. Owings said drought stress has killed dogwoods.

“In the home landscape, we forget that dogwoods prefer shade, well-drained soil and acidic growing conditions,” he said. “ So we tend to plant them in full sun and clayey soil with alkaline pH and wonder why they die or never thrive.”

“Powdery mildew is largely responsible for the loss of mature dogwood trees on the LSU campus in Baton Rouge,” Owings said.

Much of the drought loss with dogwoods dates to 1999 and 2000. Rainfall was 30 to 50 percent of normal for extended periods several times during those years.

The late 1990s and early 2000s were the beginning of increasing average summer high temperatures, as well, Owings said. Variable climate is playing a large role in the success of landscape plantings and native population dynamics, he said.

There are other Cornus species available to replace Cornus florida, he said. “Some knowledgeable horticulturists and home gardeners are planting Cornus angustata, commonly called ‘Empress of China’ which is an evergreen dogwood species,” he said.

Cornus drummondi is a shrubby native dogwood with viburnum-like flowers. In Louisiana, the silverbell (Halesia diptera) is frequently recommended as a dogwood replacement, Owings said. To see some small dogwoods in the ground as well as other work in landscape horticulture, visit the Hammond Research Station, 21549 Old Covington Highway. Take Exit 42 from I-12.

To see an old, healthy silverbell, visit LSU’s Hilltop Arboretum, 11855 Highland Road in Baton Rouge. The tree is opposite Hilltop’s office.

Ed Cullen

Advocate staff writer