Boxwood Blight Treatment and Prevention
Brian J. Stiehler, CGCS, MG
Golf Course Superintendent
Highlands Country Club
Highlands, NC
What is Boxwood Blight?
First, a blight is a generic,
all-encompassing term for a fungus that attacks a certain plant species.
Boxwood Blight, specifically, ultimately kills boxwoods after they become
infected with this fungus. This pathogen originated in a nursery near the
NC/VA boarder circa 2014-2015. It didn't start wreaking havoc in
Highlands until about 2017. It is now everywhere and if you don't treat
with a fungicide, you will ultimately lose your boxwoods. Death occurs
very quickly, in as little as 7-10 days. By the time you notice something
isn't right, it's too late.
How does this spread from site
to site?
The Boxwood Blight spore is very
sticky and easily latches on to clothes, animals, automobiles, and most
commonly, pruning shears. The spores can also travel by way of wind and
rain but that's not as common. Be careful who is maintaining your
landscape and be sure they practice proper sanitizing of tools. Applying
bleach to the equipment will kill any fungus and eliminate the chance of
infection. Shrubs that grow in damp, shady environments are also more
prone to blight. Plants need sun and air movement to thrive.
What kind of equipment would I
need to treat with?
Using a simple 1- gallon or 2-gallon
pump sprayer (available for about $15 at Reeve’s Hardware), you'll mix 2
fungicides together in the same tank and spray the boxwood with a fine mist to
get total coverage, just to the point the spray is starting to runoff the
leaves.
What chemicals do I need and
where do I get them?
1. Daconil should be mixed at 1
oz per gallon of water.
2. Tebuconazole should be mixed at 1
oz per gallon of water.
-Cleary’s 3336 is also a great choice if Tebuconazole can’t
be found. It’s available at
Highlands Lawn and Garden.
Therefore, if you have a 2-gallon
sprayer, you would put 2 oz of Tebuconazole in the tank and 2oz
of Daconil in the tank for a total of 4 oz of chemical in 2
gallons of water. These two products will ensure you have 2 modes of
action to protect the shrubs… one to kill the fungal spores on contact and the
other to protect the boxwood from within. Reeve’s Hardware sells Daconil
and sometimes Tebuconazole. Tebuconazole is a chemical name, so you will
need to read the ingredients on the fungicide label on the front of the
container, usually bottom left. Home centers typically do not carry many
fungicides, so this is pretty easy to find. DO NOT buy granular
fungicide products to sprinkle around the roots. You may think this is an
easier alternative, but Boxwoods have limited upward mobility of
fungicides. Spraying is the ONLY option!
Are these chemicals safe?
Both of these chemicals are
safe...both have the same toxicity class rating as Dawn dish detergent.
That said, I would not let your pet lick the treated boxwoods.
Now that I know what I'm doing,
how often and long do I need to do this?
Boxwoods need to be sprayed once every 21 days (3 weeks) with this chemical mixture. If you spray less than this, there will be gaps in coverage, exposing your shrubs to Boxwood Blight. They will need to be treated starting June 1 and ending in mid October. Treating November-May is not required because cold weather and or low humidity in the air prevents the fungal growth. You have to be persistent! Just because you go on vacation, the fungus doesn’t stop working. Finally, this unfortunately is a commitment for the foreseeable future. There is no way to to make shrubs immune to this blight. Plant breeders are working on resistant cultivars but those American and English boxwood in your landscape are susceptible.