Oregon 1 of 9 states to detect the disease so far
Boxwood blight has been detected in two Oregon nurseries.
Beware of boxwood blight. The invasive fungal plant disease is new to North America and has been detected in a couple of Oregon nurseries along with eight other states and a Canadian province. All eyes have been on other nurseries that potentially might harbor the disease, but there is a key role to be played by the public- especially those Oregonians who happen to have boxwood as part of their own yard's landscape.
"It's early in the process, so we have a chance of keeping boxwood blight from becoming a problem in Oregon, but it's going to take both the nurseries that carry boxwoods and homeowners to be vigilant for the diseases so it doesn't get started in our landscapes," says Dan Hilburn, administrator of the Oregon Department of Agriculture's Plant Division.
Boxwood blight, Cylindrocladium pseudonaviculatum, has previously invaded Europe and New Zealand. Boxwoods are commonly grown and sold by nurseries. ODA discovered boxwood blight disease in an Oregon nursery in December. Since that time, at least one other nursery has detected the disease. Steps have been taken by those nurseries to destroy infected plants. Unlike the pathogen that causes sudden oak death, this newly-reported disease is no threat to the state's environment and only affects boxwoods, a plant species that is not native to Oregon.
Even though the disease only affects boxwoods, it can spread rapidly. The disease doesn't spread through the air but is transmitted from plant to plant by rain splash or contaminated trimmers. Boxwood blight infects leaves and branches, causing severe defoliation and dieback. Infected branches develop long blackish-brown cankers that appear as stripes on stems. In mild, humid conditions often found during spring in Oregon, the fungus produces clusters of white spores visible to the naked eye. Although boxwoods are not typically killed directly by the disease, rapid defoliation leaves boxwoods unmarketable and unsightly.
Outside the nursery environment, boxwood blight has caused significant damage in European landscapes. That's something Oregon and other US states want to avoid.
ODA and the industry believe they have set up a good system for detecting boxwood blight in nurseries, but now needs the help of homeowners who may have boxwood hedges or individual plants.
"There are two important steps for homeowners," says Hilburn. "First, they need to be very careful when they purchase new boxwoods and only buy from reputable dealers. They should buy only healthy plants and avoid anything that doesn't appear to be perfectly healthy- even if it's on sale. Secondly, homeowners need to pay attention to the boxwoods they already have. Until now, boxwoods have been pretty much maintenance free. Now, homeowners need to look to see if those plants lose leaves when they aren't supposed to, starting from the bottom of the plant. Warm and wet conditions are ideal for the fungus and the boxwood could end up losing all of its leaves. If that happens, people need to take the boxwood out and quickly destroy it before it infects other boxwood plants in the hedge."
Homeowners are advised to sanitize hedge trimmers and trim less thrifty plants last.
Throughout the US, boxwood is an important ornamental hedge. While not as common in the Pacific Northwest, there are still plenty of places where boxwood is a featured landscape ingredient. Anyone who has walked the grounds of Oregon's State Capitol in Salem has probably seen the attractive boxwood hedges.
As one of the nation's leading nursery production states, Oregon produces a good share of the boxwoods on the market. About 200 Oregon nurseries grow many different varieties, with most of them going out of state. That's why ODA is concentrating a lot of effort on surveying Oregon nurseries for the disease.
"If we can keep the nurseries clean, that will help keep the disease from getting out into the landscape," says Hilburn. "It's highly unlikely now that boxwood blight can be eradicated from the continent. Nurseries need to learn how to keep it out of their production and clean it up when they find it. But homeowners also need to be aware of boxwood blight, be vigilant in looking for it, and being careful where they buy boxwood."
The disease is serious enough to have prompted a pest alert by the Oregon Department of Agriculture. That alert targets nurseries but also underscores the importance of educating the public. Having additional eyes looking for any sign of boxwood blight in Oregon's yards, gardens, and landscapes can help detect outbreaks early, allowing for quick action to keep it from spreading. Anyone encountering a boxwood hedge or plant showing symptoms of the disease are encouraged to report it to ODA or their county Oregon State University extension agent. Officials can confirm the disease and would like to track any plant that has developed boxwood blight. A digital picture can be sent to ODA or a sprig from the boxwood plant can be placed in a bag and delivered to ODA's Plant Division.
One positive about this latest invasive disease of Oregon plant life- boxwood blight does not approach the threat of sudden oak death in Oregon. Since there are no native boxwood species in the state's natural environment, officials don't have to deal with an outbreak in the wild. Sudden oak death has established itself in Curry County along the southern coast. Still, the two diseases share a common bond.
"The best way to deal with sudden oak death and boxwood blight is to not let it get started in the first place," says Hilburn. "That's why this is an important topic. We need people to be aware of their boxwoods. If something doesn't look the way it is supposed to, they need to check it out and take steps to keep the disease from spreading. If everybody has that attitude and vigilance, we can stop this disease."
For more information, contact Dan Hilburn at (503) 986-4663.
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