Boxwoods dying - Ask Extension
We just removed two boxwoods that were either completely brown or had many dead brown branches. We are probably going to remove the remaining 4 but we...
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Boxwoods dying #864022
Asked April 10, 2024, 7:00 PM EDT
We just removed two boxwoods that were either completely brown or had many dead brown branches. We are probably going to remove the remaining 4 but we’re hoping to save our conical boxwoods in same bed. Wanted to see if you could help us determine the problem they are having. Once we remove them, we also wanted to see if it would be safe to plant new shrubs immediately. Thank you!
Howard County Maryland
Expert Response
The damage pictured appears to be caused mainly by mites; it's heavier damage than we usually see, since they are not typically a serious boxwood pest. Mites tend to outbreak when plants are treated for other insect pests (were they sprayed in the past with an insecticide?) and in situations when plants are stressed by reflected heat, drought, or over-pruning. The location of the boxwoods near a wall and close to the structure implies the air circulation keeping them cooler in summer might not be ideal, especially if it happens to face south or west. Are the plants monitored for watering needs during periods of hot or dry weather? Last year, for example, most of Maryland experienced some degree of drought for much of the entire growing season. Boxwood roots are relatively shallow for a shrub, and are not very tolerant of extremes of soil dryness or wetness. (Is there a roof downspout outlet that empties near the planting?)
The brown branch tips are hard to diagnose since they can be caused by several factors. Volutella Blight is a typical reason, but isn't necessarily what is happening here. You can learn more about common boxwood ailments in our boxwood diagnostic web page.
Shearing is commonly practiced on boxwoods because people find the manicured look appealing, but it's not the best pruning technique and can make the plant more vulnerable to pest and disease outbreaks. The reason is partly because the dense outer layer of foliage shearing creates reduces airflow; it also shades the interior foliage to a greater degree, causing it to fall off prematurely. (Eventually, inner, older leaves will shed anyway, but this exacerbates that phenomenon.) Instead, pruning should only be used to lightly shape a plant (if desired, as it's not necessary for plant health) or to moderately maintain its size, though ideally a cultivar is selected that will fit into a space without relying on pruning to keep it contained.
Foliage cannot heal, so damage is permanent for the life of an individual leaf. Since evergreens retain leaves for several years before shedding them, that means any insect feeding damage or infection eyesores will remain until that leaf falls. New growth can help to hide it, but in this case, we're not sure how well the stressed plants would regrow and if it would be enough to refresh their look in a couple years (or longer).
One option is to severely cut the shrubs back to within about 1 foot of the ground, forcing regrowth that will eventually bring them back to their current size. Granted, due to the naturally slow pace of growth in boxwoods, that may take several years. Replacement is also fine if you prefer a more instant fix, but be aware that the site conditions that allowed for a mite outbreak in the first place may cause a repeat occurrence, and there isn't a preventative pesticide we would recommend using (nor would one work well anyway) to keep that from happening again. While some cultivars of boxwood (and there are dozens on the market) have more inherent resistance to certain pests (like Boxwood Leafminer) and diseases (like Boxwood Blight), none are immune to all, and we are not aware of any that are resistant to mite damage in particular. In fact, unfortunately, it's been noticed that some of the new resistant cultivars appear to be more vulnerable to mites.
Using a different species of shrub is certainly an option. If you would like ideas of what to try, we'd need more information about the site conditions: how much direct summer sun it gets, how well the soil drains (and if it skews dry or wet), if deer browsing is a risk, and what mature height the area can accommodate. Whether you prefer the plant be evergreen is another consideration. Using a mix of species instead of a mass or row of only one is also helpful to reduce the risk of future problems becoming widespread.
Few boxwood issues would remain in the soil to affect new plants. One of them is Boxwood Blight (not indicated by your symptoms), since spores can remain infectious on the soil around affected plants for several years. Therefore, in this situation, you likely don't have to worry about the soil itself, barring any issues with drainage.
Miri
The brown branch tips are hard to diagnose since they can be caused by several factors. Volutella Blight is a typical reason, but isn't necessarily what is happening here. You can learn more about common boxwood ailments in our boxwood diagnostic web page.
Shearing is commonly practiced on boxwoods because people find the manicured look appealing, but it's not the best pruning technique and can make the plant more vulnerable to pest and disease outbreaks. The reason is partly because the dense outer layer of foliage shearing creates reduces airflow; it also shades the interior foliage to a greater degree, causing it to fall off prematurely. (Eventually, inner, older leaves will shed anyway, but this exacerbates that phenomenon.) Instead, pruning should only be used to lightly shape a plant (if desired, as it's not necessary for plant health) or to moderately maintain its size, though ideally a cultivar is selected that will fit into a space without relying on pruning to keep it contained.
Foliage cannot heal, so damage is permanent for the life of an individual leaf. Since evergreens retain leaves for several years before shedding them, that means any insect feeding damage or infection eyesores will remain until that leaf falls. New growth can help to hide it, but in this case, we're not sure how well the stressed plants would regrow and if it would be enough to refresh their look in a couple years (or longer).
One option is to severely cut the shrubs back to within about 1 foot of the ground, forcing regrowth that will eventually bring them back to their current size. Granted, due to the naturally slow pace of growth in boxwoods, that may take several years. Replacement is also fine if you prefer a more instant fix, but be aware that the site conditions that allowed for a mite outbreak in the first place may cause a repeat occurrence, and there isn't a preventative pesticide we would recommend using (nor would one work well anyway) to keep that from happening again. While some cultivars of boxwood (and there are dozens on the market) have more inherent resistance to certain pests (like Boxwood Leafminer) and diseases (like Boxwood Blight), none are immune to all, and we are not aware of any that are resistant to mite damage in particular. In fact, unfortunately, it's been noticed that some of the new resistant cultivars appear to be more vulnerable to mites.
Using a different species of shrub is certainly an option. If you would like ideas of what to try, we'd need more information about the site conditions: how much direct summer sun it gets, how well the soil drains (and if it skews dry or wet), if deer browsing is a risk, and what mature height the area can accommodate. Whether you prefer the plant be evergreen is another consideration. Using a mix of species instead of a mass or row of only one is also helpful to reduce the risk of future problems becoming widespread.
Few boxwood issues would remain in the soil to affect new plants. One of them is Boxwood Blight (not indicated by your symptoms), since spores can remain infectious on the soil around affected plants for several years. Therefore, in this situation, you likely don't have to worry about the soil itself, barring any issues with drainage.
Miri
