Boxwood blight (and Impatiens blight if you want)

Hi Guys! I'm never around any more, because Congress decided I needed to do the work of two people. However, the two of us are working on lots of interesting projects. In addition to Sudden Oak death, I'm now working on the two new diseases of boxwood and Impatiens. I assume we don't much care about Impatiens (although I'll grudgingly admit they are cute and easy), but we DO care about boxwood. Boxwood blight is a new disease that came here from Europe a couple years ago. It's a fungal disease that defoliates plants and eventually kills them. There is no real treatment at the moment besides a) constant application of fungicides b) use of resistant cultivars (mostly microphyllas) c) pruning for good air circulation.

Any questions? Ask away! I'll even answer questions about Impatiens, but the answer is going to be "don't grow them any more".

Hi Nina,
What part of the country is currently affected? You mention that B. microphylla is resistant, so I assume the area to watch is New England, where the B. sempervirens is used? Down here, we seem to have 95% B. microphylla in the landscape.
Thanks!

Right now it's the east coast, from NC to CT, roughly. You are correct that the real tragedy is B. sempervirens suffruticosa, especially in historic gardens like Mt. Vernon, Dumbarton Oaks, Monticello, etc. Any boxwood that is trimmed is in danger of being disfigured by this disease, and also to be spread by the person doing the pruning (reportedly, the disease can also be spread by dogs).

Just thinking about those old OLD Box plantings up there makes me sad to think they are at risk. I hope a treatment is discovered soon! Thank you for posting this; it reminds us to appreciate what we have and also to clean our tools.

Are there specific fungicides that work better than others for this problem? Daconil, copper, etc? And what does "constant" mean? Applied once a month, once a week, after every rain?

There are some pesticides that are better than others: Colleagues at NC State are working on this: http://plantpath.cals.ncsu.edu/sites/default/files/u33/Ivors%20boxwood%20blight%20fungicides%2012_0.pdf

"constantly" means (of course) in accordance with label directions, but means not missing applications. This pathogen puts out an AMAZING number of spores per leaf. And I say that as someone who sees lots of spores. If your boxwood has only one infected leaf, it will soon be exposed to thousands of spores.

Hi Nina,

It's really nice to hear from you even though it's bad news! I love my boxwood bonsai which are very old and have had no problems yet.

I have two questions:

Do you feel the danger comes from earth grown boxwoods and have you see this in boxwoods bred for bonsai? Two of my boxwoods are air layers from a very old California bonsai and have only been grown in bonsai soil.

I had an Ilex yaupon (holly) which I always treated like boxwood that died last year from a very rapid spreading fungus. None of my boxwoods show signs of the disease and I took measures to separate the sick bonsai. Have you heard of this fungus attacking holly?

Kindly,
Norma

Nina, do you mind explaining what's going on with imaptiens?  We are asked to plant lots of them and I hate scratching that plant off the summer list.  It seems to be hit and miss, some do just fine while others are a complete washout.  Does any fungicide work?  I'm not really interested in and expensive and time consuming fix so I guess the point is moot...

A few years back we had the same problem with annual periwinkle, but that seems better now.

R

Nina only gets here when she has time, but I suspect this is what she's talking about:

http://www.purdue.edu/newsroom/releases/2013/Q2/purdue-specialist-warns-of-disease-deadly-to-impatiens--.html

There's more if you Google 'disease affecting impatiens'.

Hi Norma!

This is a problem that's spreading with new material coming out of nurseries. people are being advised not to buy new stock without being VERY careful, and that's good advice from what we know at the moment, because the organism doesn't seem t spread far in the wind. If you have box, and you don't move any new stock in, you should be fine. Holly doesn't get this disease.

Russell:

It IS hit or miss at the moment, but I just heard of a report on Long Island, so this disease is present this year. Downy mildews need wet weather, but they spread really well in wind, so once this begins to move, it will start to take out plants. Many, many fungicides are effective, but the whole point of Impatiens is its cheap, easy nature. If you have to spray it constantly, what's the point? Put in Petunias (which is what the entire state of Maryland appears to have done).