Growings On: Boxwood blight increasing in Georgia

Roger Gates

March is predictably a rainy month in Northwest Georgia. Eleven days of rain in Dalton produced a monthly precipitation total of over 14 inches. An average March total would be just over 6 inches. Adequate moisture is always beneficial, but persistent excess can be detrimental. Brown areas in your landscape trees or hedges may be the result this year. Wet winters and severe weather have been causing disease and other issues in landscape plants, especially Leyland cypress and boxwood.

Over the last few years, there has been an increase in samples of these species to the University of Georgia's Plant Disease Clinic, according to Extension plant pathologist Jean Williams-Woodward in the College of Agricultural and Environmental Sciences.

Boxwood blight, first discovered in Georgia in 2014, has hit hard in established landscapes. Rapid defoliation is a characteristic symptom of boxwood blight that separates it from other boxwood diseases, and it can move quickly through landscapes, especially with wet weather.

Leyland cypress are one of the most popular landscape plants because of quick growth. However, there are a number of issues that could affect the plant, sometimes several factors simultaneously.

"They are dying I'm afraid -- and it's kind of expected," said Williams-Woodward, who tracks diseases in ornamentals for commercial nurseries and greenhouses. "There are several things that are going on and all are coming together at this point. It's the lifespan of the trees, poor root systems, really wet conditions and drought stress we had before that. It's a lot of compounding events that seem to be causing issues."

The lifespan of the Leyland cypress is relatively short in Georgia, around 15 to 20 years. Hot summers, much warmer than Scotland, where the species was bred contribute to limited longevity. Summer drought stress combined with wet winters and other extreme weather can cause root issues.

Leyland cypress is sometimes susceptible to other disease and insect issues. If Leyland cypress is showing a lot of brown branches or thinning canopy, there's not much you can do to save it, according to Williams-Woodward.

"You can prune some branches to make it look better, but you're not suddenly going to turn it into a green, healthy tree again regardless of what you do. I don't recommend applying fungicides mainly because some of these trees are very large and you'd have to get it high into the air and do applications year-round," she said.

Boxwood leaves infected with boxwood blight develop leaf spots, turn brown and readily drop from the plant, leaving bare stems and black stem lesions visible. Leaf spots can develop within days of infection and defoliation occurs within two weeks.

Once infected with boxwood blight, the disease is very difficult to control. Infected plants should be removed and disposed of in the trash along with any debris. All tools, shoes and clothing must be disinfected afterward to reduce carrying fungal spores to healthy boxwoods.

If you're looking for alternatives for Leyland cypress or boxwoods, UGA experts have a few different options.

Japanese cedar (cryptomeria) and "Green Giant" arborvitae are two common recommendations similar in size to Leyland cypress for screening or hedges. Other possible choices include Brodie eastern red cedar (also called Brodie juniper) and spartan juniper.

Japanese, dwarf yaupon and inkberry hollies are boxwood look-alikes with a similar texture and compact form.

Korean boxwoods are generally considered more resistant to boxwood blight. However, it is still unclear exactly which varieties of boxwood are more tolerant of boxwood blight in Southern U.S. gardens. Williams-Woodward and Extension horticulturist Matthew Chappell are developing evaluations of dozens of cultivars from the U.S. National Arboretum's boxwood collection.

With summer coming soon, new plantings should be deferred until this fall. Correct drainage or other issues before planting. Till the soil well to break it up and reduce compaction, and reduce water that might be pooling around the base.

Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at roger.gates@uga.edu.

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