Boxwood Blight A New Concern For Landscapers And Gardeners

By Nancy K. Crevier

Gardeners need to be cautious, but there is no need to panic over the news that boxwood blight, caused by the fungus Cylindrocladium buxicola, has been identified in Fairfield County, said Dr Sharon M. Douglas of the Connecticut Agricultural Experiment Station (CAES) in New Haven.

The blight was first identified in the state in October, said Dr Douglas, after samples were submitted to the New Haven Experiment Station. Those samples were sent for further testing to the USDA Animal Plant Health Inspection Service, which positively identified the fungus that is deadly to nearly all varieties of boxwood used extensively in landscaping in this area.

According to a report posted by Dr Douglas on the CAES website December 8, the disease was first identified in New Zealand in 2002, and has since been reported throughout Europe, where it is considered to be of great concern. It is not known how the blight was introduced into the United States, she said.

“We don’t really have a handle yet on how widespread it is in Fairfield County,” said Dr Douglas, but inspectors have been finding it in a number of different locations, including distributors, nurseries, and in residential landscape situations.

The disease affects leaves and stems of the boxwood, but does not appear to affect the roots. Leaves may show light or dark brown spots with dark borders that enlarge as the disease progresses. The infected leaves turn completely brown and fall off, shortly after symptoms first develop.

Dark brown to black stem lesions, in a diamondlike pattern, may also indicate infection with Cylindrocladium buxicola.

Boxwoods are susceptible to fungal attacks due to the very nature of the plant that has made it the most popular landscaping plant in the United States, said Dr Douglas. A tight, compact canopy does not allow for good air circulation, and thick, waxy leaves stay wet longer.

Steve Fancher, co-owner of Shakespeare’s Garden in Brookfield said that the garden center has not yet encountered boxwood blight in the nursery stock, nor have clients reported it to him.

“We have several varieties of boxwoods in the nursery,” said Mr Fancher, “including Green Mountain, Winter Gem, and Suffruticosa, an English dwarf variety, all of which I understand are susceptible.”

Distributors have not cautioned buyers about the potentially devastating disease, to his knowledge. “A lot of times, when things like this come up, distributors don’t want to talk about it,” he said.

A lot of preventing the spread of fungal diseases is related to cultural practices, Mr Fancher said. He and his staff are advising clients with boxwood plantings to be careful not to overwater or water overhead, and to not wet down the plants at night time, when they do not have time to dry out. “You don’t want to plant boxwoods too closely to each other, either,” he said. Preventative sprays would be another alternative if there were a fear of boxwood blight affecting a landscape, said Mr Fancher.

Wait And See

Because the disease has been diagnosed only recently, Hollandia Nursery’s owner Eugene Reelick said that they have not yet seen evidence of boxwood blight in any of the local nursery jobs or on either of the Hollandia nursery sites.

“There’s a lot of excitement, but we need to see what’s going to happen,” said Mr Reelick, who admitted to being nervous, anyway, since his company uses boxwoods heavily in landscaping. “Deer don’t eat it, it’s attractive, and it can be manicured to any form. We use a lot of boxwood. If you’re a nurseryman, you had better be concerned. It’s not good for any of us,” he said.

Mr Reelick emphasized the need for integrated pest management and preventative measures to stop the spread of boxwood blight. The problem is that American nurserymen have not had enough time yet to discover what works against this fungus. “Boxwood blight has been in Europe for several years, and I have to wonder why they have not come up with an answer,” he said. He is hopeful that a more aggressive approach by American growers and scientists will result in a fungicide that will stop the blight in its tracks.

“I really, really hope we find a resolve to this,” said Mr Reelick, and added that for now, at least, cold weather will put the spread on hold.

“Plants affected will not recover,” stated Dr Douglas, and experience overseas indicates that the fungus is likely to overwinter. “It has been found in very cold areas of Russia, so chances are, it will survive the Connecticut winters,” she said.

Todd Gay of Landscaping Unlimited in Newtown is also relieved to have not yet seen any signs of boxwood blight in his plantings, “and we do use a lot of boxwood,” he said.

His company will be using extra precautions come spring cleanup time, he said, and looking carefully at all boxwoods in the landscapes to identify any problems early on. They may recommend some preventative spraying, but that is difficult because of the tight growth nature of the boxwood, he said, and every leaf surface must be covered in order for a fungicide to be effective.

Take Precautions

Home gardeners must be very careful, come spring, when introducing new boxwood plants into a landscape, said Mr Gay, to be certain that the plant is clean. Buying from reputable, local growers is essential, as large box stores do not have employees experienced enough to recognize symptoms of boxwood blight, and can unknowingly allow it to flourish and spread. Cleanup of any dropped leaves around boxwoods is very important, added Mr Gay.

Cleanup of leaf debris is essential to stopping the spread of boxwood blight, agreed Dr Douglas. The area from which a diseased boxwood has been removed should be thoroughly cleaned, and all dropped leaves raked up, bagged, and tossed into the trash. Do not put diseased boxwoods or leaf debris in to a compost pile or dump in the woods.

The blight spores are “splash-dispersed and can be carried by wind or wind-driven rain over short distances,” according to Dr Douglas’s report. Because the spore is sticky, it can be spread by animal, bird, or human contact. Asymptomatic boxwoods, those that are infected but do not yet show signs of disease, can also spread the fungus.

“There are all kinds of insects and issues with boxwood, so it’s not surprising to hear about this blight,” said Dan Holmes, of Holmes Fine Gardens.

The very popularity of the boxwood in this area is part of the problem, he said. “Monoculture of anything can invite problems and devastate your landscape. Diversity in landscaping is very important. I’m always leery when I see one plant used too often,” Mr Holmes said.

He suggested several deer-resistant options to the nonnative boxwood plants. The native rhododendron, leather leaf viburnum, sweet box (sarcococca humilus), or skimmia japonica are all plants that can add visual interest to the landscape, and are not susceptible, so far as Mr Holmes is aware, to the boxwood blight.

The andromeda shrub is a good choice for more shaded areas, he said, although deer may take a nibble from it.

“We need more options in our industry,” Mr Holmes said.

It is crucial that suspected boxwood blight is correctly diagnosed, Dr Douglas said. “Boxwoods have a number of other common problems, and what appears to be this blight could be one of those. We had a very wet season, conducive to many fungus problems. Every spot is not necessarily boxwood blight,” she cautioned. Suspected boxwood blight should be reported to the Plant Disease Information Office by calling 203-974-8601 (toll free 877-855-2237).

“The weather hasn’t helped this year, and the extended warm fall this year has not been good for boxwoods, either,” Dr Douglas noted.

Even if Cylindrocladium buxicola is positively identified in a plant, it does not mean that nearby boxwoods must also be disposed of. It is possible to contain the disease by properly removing — and that includes digging up the entire plant — the infected plant. Bagged, diseased boxwoods can be thrown in municipal trash, or they can be buried.

Currently, there is no curative for Cylindrocladium buxicola, Dr Douglas said. Fungicides registered for use in Connecticut include chlorothalonil and mancozeb. They must be applied regularly to nonaffected plant stock and may be useful in preventing the spread of boxwood blight to healthy plants. Plants already infected will not be helped by fungicide applications.

“This is not the end of the world, though. People should just be on alert, get any suspected plant properly diagnosed, and handle it as needed,” she said.