This afternoon, I spoke at length to a plant pathologist at NC State University, Dr. Sara Vallani, who is the lead researcher on Boxwood Blight. Here are a few questions I asked and her response:
1. What is the current outlook with regards to Boxwood Blight? Is it as dire as once thought?
This remains a critical, important issue and research is being funded to the tune of $500,000 a year.
2. At a small education event in Highlands last year, an "expert" claimed that all boxwoods would be gone in 3-5 years? Do you think there is any truth in that?
While there is truth to the statement, there are many ways you can safeguard yourself against this blight. These include proper sterilization of pruning tools, purchasing your own tools that never leave your property and finally fungicide treatments during the growing season.
3. Any thoughts about why this may not be an issue this year given the large amount of rain we've received thus far? In 2016, it was extremely dry except for a 2 week period in July. During that time, we received nearly 9-10" of rain in 14 days and Boxwood Blight exploded in a number of areas around Highlands. Personally, I felt the this fungus would have been a big issue during the 2017 season provided Highlands returned to its normal seasonal weather patterns.
Sara agreed that it hasn't been an overly dramatic year for the blight. However, the fungus over winters in a very hardy structure- usually in/on the ground- that remain alive for 6-7 years. The spores can lay dormant and spores can be released at any given time. More research is being directed at this very issue. It does remain somewhat a mystery as to why the boxwood blight wasn't overly active this year given the excess rain events.
4. In regards to fungicide use, it seems everyone is recommending chlorothalonil (Daconil Fungicide) as the most effective treatment, but why are systemic fungicides never mentioned?
Daconil is very effective but when its combined with other fungicide classes, it offers better protection. Keep in mind that fungicides have limited systemic capabilities in shrubs like boxwood. A fungicide will not be very mobile in woody tissue but will translocate through the leaves. Therefore, all applications must be made using a sprayer to the foliage. Applications should be made every 14-21 days depending on weather and the products used.
5. Finally, what is the most effective chemical treatment at this point and at what application interval?
Keeping your tools clean is the first line of defense. Make sure your landscape contractor either properly cleans their tools or use tools that belong to you and are used only on your landscape. The disease spores are small and "very sticky." This means they will attach to clothing and tools very easily but they will not travel easily by wind.
The age of your boxwoods has no effect on the disease. There are some indications that MAYBE older boxwoods have developed some resistance to the blight. That is being studied. While both American and English Boxwoods are susceptible to the blight, most Asian varieties are resistant. Over time, you will see more of a shift to the use of these Asian species.
This was an interesting conversation and look forward to Sara coming to Highlands during the month of September. If you have any interest in speaking with her during her visit, please let me know and I can arrange for that. In the last 2 years, it's been difficult to find "experts" in this area given how new the problem is. Sara moved to NC State last year after a number of years at Cornell University in Ithaca, NY.
