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Over the past two years, a fungus that infects and deteriorates boxwood plants has rapidly spread to different localities in the state of Virginia.
Although previous attempts to eradicate the boxwood blight from spreading to other plants have failed, experts are still attempting to curb the epidemic and are encouraging members of the community to help.
On Nov. 7, the state Department of Agriculture and Consumer Services [VDACS], along with the Virginia Cooperative Extension, held a meeting at the Virginia Department of Forestry office in Galax.
Several local boxwood growers, including hobbyists and local business owners, attended the meeting to learn more about the disease and how to contain it.
History of the Blight
The VDACS Office of Plant Industry Services’ Southwestern Regional Supervisor Edward Burlett began the meeting with a history of boxwood blight in the area, which began with an instance in Lambsburg in October 2011. According to their trace, the disease was carried in on a boxwood from a grower in North Carolina. “The infected plants had been brought into the state, and [the grower] didn’t know why they were suddenly dying back,” said Burlett.
Another group of boxwood plants showed signs of infection in February 2012. As shown in a photo Burlett provided on the Powerpoint slideshow on the wall behind him, only some of the grower’s plants were showing symptoms of the blight. The visibly infected plants were destroyed, but the grower was reluctant to wipe out the rest of his inventory. “They asked us to leave them the ones that were still good... and in July of that year, they developed boxwood blight, as well, and were also destroyed,” Burlett said.
After that incident, Burlett and other inspectors continued to carefully monitor the areas in Lambsburg, but continued to find symptoms in other areas this year.
Today, boxwood blight has been found in several areas throughout the region, including Richmond, Chesterfield County and, as of this month, Fairfax County.
“Boxwood has a way of getting around. It’s usually people who help it, but it’s getting around,” warned Burlett. He clicked over to a map, showing the progression of the disease over the past two years. The slides progressed from one small area to splotches spread in several areas all over the map, covering more than five times more ground than the first slide. “This is what you are going to have in a valley that will never sell any boxwood. If you don’t take care of it right, you are going to have it, your neighbors... everybody.”
In other areas of the country, boxwood blight has made appearances mainly along the eastern seaboard in the northern states, reaching down to areas in North Carolina. Oregon and Washington have also seen infected boxwood plants.
How the Disease Progresses
Chuan Hong, Virginia Cooperative Extension professor of plant pathology, explained how the disease spreads to other plants. Hong has studied the disease, and recently traveled to London, another prominent area that has seen boxwood infection.
Hong explained that boxwood blight needs three components to exist: the disease pathogen (the blight itself), a susceptible host (the plant) and an environment that will foster the growth of spores on the plant.
Weather, Hong explained, was a large factor in the survival rate of the pathogen, and noted that it grows best in 25˚C or 77˚F. The disease also needs a wet environment in order to thrive, he said.
Signs of boxwood blight infection include defoliation, black spots on leaves and blackened stems. Although the presence of the above characteristics does not confirm that the plant has boxwood blight, plants with these symptoms should be examined to determine the cause.
Mary Ann Hansen of the Virginia Tech Plant Disease Clinic warned the audience that there are other plant infestations that can resemble boxwood blight — volutella blight, which browns leaves; and root rot disease, which browns stems but does not leave black marks or spores on the plant.
The blight is not an airborne pathogen, but it can be spread by spores that stick to shoes, gloves and gardening tools, where they can survive up to six weeks.
Preventing Further Spread
Larry Nichols, program manager of the Office of Plant Industry Services, explained that his office works to regulate the spread of plant pests, including insects and disease. The office does an annual registration of all nurseries, where they visit and inspect the plants for signs of pests.
“This is done to protect consumers, and it also serves to protect the nursery. Nurseries that pass get a certificate indicating that their nursery stock is pest-free,” Nichols said.
Commercially, the organization can issue destruction or stop-sale orders, which are effective in preventing further spread of a particular pest. “In the boxwood blight situation, we issued destruction orders because we were at a point in the infection in Virginia that we felt that we could still handle it... but we realized over this past summer that we have lost control,” he said.
Instead of destruction, they have now moved to stop sale orders to prevent the movement of infected plans to other nurseries or personal properties. “We do still recommend destruction, as it is still the best method,” said Nichols.
Although the office has the authority to either destroy or quarantine commercially owned plants, they lose that authority when a plant is purchased and moved to a residential location.
To help experts in their battle to contain the blight from spreading further, residential and commercial growers are being asked to take several steps in protecting both their plants and neighboring plants.
Sanitation practices, such as cleaning gardening tools and boots, and destroying plant debris or “leaf litter” are encouraged to kill the pathogen before it has a chance to tag onto other hosts. Effective sanitizers include bleach (1:10), hydrogen peroxide, lysol, and ammonium compounds such as Greenshield and Kleengrow.
It was noted at the meeting that Clorox bleach should be used instead of other generic brands, as the Clorox brand is EPA-certified.
Shoes should also be disinfected after visiting infested or suspect sites.
Preventative measures can also be taken, according to Hong, by spraying uninfected plants with a fungicide every seven to 14 days. Suggested fungicides included Daconil Weatherstik Spectro 90WDG, Concert II, Torque, Tourney 50WDG and Medallion WDG.
Growers that suspect that their plants might be infected with boxwood blight should contact the VDACS at (276) 228-5501.
Samples of potentially infected plants can be submitted to the Virginia Tech Plant Disease Clinic for tests through the local Virginia Cooperative Extension office. Plants or samples of plants should be double-bagged and sealed to prevent further spread. Plants should be sent at the beginning of the week to prevent the shipment from deteriorating further over the weekend.
Commercial samples of plants believed to be infected with the blight can be sent to the VDACS by contacting (804) 786-3515.