Boxwood blight

Boxwood blight (also known as box blight or boxwood leaf drop) is a disease of boxwoods caused by the fungus Cylindrocladium buxicola (also called C. pseudonaviculatum).

History

The first description of boxwood blight was from the United Kingdom in the mid 1990s. In 2002 it was discovered in New Zealand. At that time the cause was identified as a new species of fungus and formally named Cylindrocladium pseudonaviculatum. The fungus causing the disease in the U.K. was later named C. buxicola. These are now known to be the same.[1]

It is found throughout Europe.[2][3]

In October 2011 the blight was found in North Carolina and Connecticut. By January 2012 it had also been identified in Virginia, Maryland, Rhode Island, Massachusetts, Ohio, Oregon, Pennsylvania, New York and British Columbia.[4]

Hosts

There appears to be some tolerance to the disease within the Buxus genus. In general, the boxwood varieties within the species sempervirens tend to be more susceptible to this disease; this would include the most popular varieties 'English' and 'American' boxwood.[5]

Other plants within the family Buxaceae, such as Pachysandra terminalis, as well as a Sarcococca species, have also found to be susceptible to this fungal pathogen.

Symptoms and disease process

The blight initially presents as dark or light brown spots or lesions on leaves. The leaves typically turn brown or straw color, then fall off.[6] The stems develop dark brown or black lesions.[7]

It is often fatal to young plants.

The spores are dispersed by wind and rain over short distances. Since they are sticky they are probably also spread by birds, animals, and contaminated clothing and footwear. The commonest mode of transmitting the blight is the introduction of asymptomatic plants, or plants treated with fungicide (which can mask the disease) to areas with uninfected plants.[8] Warm and humid conditions facilitate its spread.[9] The fungus does not need a wound to infect a plant, but it does require high humidity or free water.[10]

The disease can surivive for five years in fallen boxwood leaves.[11]

Prevention and treatment

There are a number of steps that can be taken to prevent the spread of the blight:[12]

There is no known cure. Fungicides may prevent the spread of the disease. To be effective, they must be applied to the entire plant, leaves and stems. This can be difficult because boxwood leaves are very closely spaced.[13]

Since this is a new disease, research is ongoing. There are a few places to find out current information, including: the Connecticut Agricultural Experiment Station Plant Disease Information Office, the ANLA boxwood blight website, and the North Carolina State University boxwood blight links page.

Notes

  1. ↑ Douglas. p. 1
  2. ↑ Douglas pp. 1–2
  3. ↑ Milius
  4. ↑ Milius
  5. ↑ http://go.ncsu.edu/boxwood_blight_links
  6. ↑ Douglas, p. 2
  7. ↑ Milius quotes Lynn R. Batdorf, curator of the National Arboretum's boxwood collection (currently not infected): “I’ve never poured diesel fuel on a boxwood, but if I did, that’s what it would look like.”
  8. ↑ Douglas, p. 6, calls this "Trojan horse " or "Typhoid Mary" transmission.
  9. ↑ Douglas, p. 5
  10. ↑ Douglas, p. 6
  11. ↑ Douglas, p. 7
  12. ↑ Douglas, pp. 8–9
  13. ↑ Douglas, p. 9 has details on various fungicides

References

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