Mid-Atlantic Grower columns

Garden Talk

Winter

(February 2012)

By CAROL KINSLEY, Editor

It’s supposed to be winter. One day it snows and another is warm and sunny, tempting me back into the garden. I think it’s the wild temperature swings that killed my smaller frog, which I raised from a tadpole (like I had much to do with it other than dumping him in the pond!). Either that or he’s hibernating lying on his back atop the filter. I need to fish him out.
I’m done with the leaves until spring! The machine is packed away and the mountains of leaves are just sitting there. Hopefully come truly warmer weather I can get them into my compost bins, properly layered with a nitrogen source and some water.
Meanwhile, I’m signing up for Master Gardener activities right and left, as though I had nothing else to do. Being with others who love gardening as much as I is a joy!

 

One Up on Bugs

Boxwood blight

By Stanton Gill, Regional Specialist, Central Maryland Research and Education Center, University of Maryland Extension

(February 2012)

Boxwoods have made a huge comeback in the marketplace with many new plant forms, leaf size and shapes, leaf colors, textures and, of course, pretty good resistance to deer browsing. Enter ‘New Kid on the Block” — boxwood blight, Cylindrocladium buxicola.
Is the party over for boxwood fans? Well, maybe and maybe not, but this new invasive disease from Europe has the potential to wreak havoc in the boxwood world.
Cylindrocladium buxicola, boxwood blight was first discovered in Great Britain in 1998. Spreading quickly through southern England, by 2001 it had spread to Ireland, Belgium, Italy, France, Holland and surprisingly, New Zealand. In 2004 it was identified in the United States near Philadelphia and has quickly spread to other regions. In Connecticut, some nurserymen are destroying infested plants by rouging out plants and burning them.
As with all other fungal boxwood diseases, Cylindrocladium buxicola prefers high humidity, moderate temperatures, 77 degrees F. and poor air circulation. This disease has proved particularly acute in England where boxwood is tightly and regularly sheared, resulting in dense foliage, and planted too close to other plants, both of which result in poor air circulation. This boxwood blight is primarily limited to Buxus sempervirens ‘Suffruticosa’.
Symptoms to watch for
Cylindrocladium buxicola is primarily a problem of leaves and causes twig blight. In the early stages of infection the fungus produces visible brown spots. These spots rapidly enlarge and coalesce, causing defoliation, and form black streaks on the bark. The black streaks appear to progress from the bottom to the top of plants. Patches of whitish or grayish fungus may be visible on the lower leaf surface under moist conditions.
Symptoms usually appear during the fall and winter season, producing their damage to the twigs in spring. While only severe injury has been observed, chronic infection can result in a severe weakening, contributing to death of the boxwood.
What can be done?
Cultural action: The most important technique to avoid and correct this blight is to encourage free circulation of air through the interior portions of the boxwood. Annual thinning of the dense foliage in fall will greatly improve the air circulation, providing an unfavorable site for the blight. Boxwood grown in sunny locations has more dense foliage, requiring more frequent and more aggressive thinning. Because shearing Buxus sempervirens ‘Suffruticosa’ pro-duces dense foliage, it encourages the development of Cylindrocladium and is not recommended. Sanitation is an important preventive measure as infected foliage in the debris can cause re-infestation.
Improving the air circulation around the exterior portions of the boxwood is also important. Boxwood plants growing together in a hedge or specimens touching each other are two common situations that can limit air circulation. Even one boxwood planted on the inside corner of, or next to, a building, fence or hedge can have poor air circulation. In these examples, reducing the overall density of the planting will help.
Chemical control
There is very active research going on in Connecticut and the Carolina University Extensions to find the best chemical control for this newly introduced disease. In Connecticut, Extension specialists are recommending that commercial nurseries follow preventive fungicide programs that include different modes of action (FRAC groups). Among the fungicides registered for use are azoxystrobin, boscalid and pyraclostrobin, chlorothalonil, fludioxonil, kresoim-methyl and mancozeb.  There will be more coming out on the best fungicides for controlling this disease as information is released from University Extension and Experiment stations in 2012.
Hang in there
Boxwoods will survive this latest onslaught but you will have to be vigilant to prevent major damage in 2012.