Boxwood Hedge

Question: Our boxwood hedge (approx 4 feet tall and 30 feet long) has a large dead section for several feet starting a bit past the middle and under low hanging cotoneaster shrubs. The damage appeared some time after the freeze that occurred several weeks ago but since the heat a couple of weeks ago many of the branches in the center seem to have collapsed.  There are 30 plants in the hedge and the trunks are from 3-6 inches wide. The hedge is at least 40 years old and could be as much as 70 years old. There are long sections which appear healthy on the sides and top and the leaves do not seem to have necrosis or signs of disease (checked OSU site for boxwood blight). Even the part with the dead section in the center seems to be healthy on the sides. We would really like to save this hedge as it is a feature of our garden. Please suggest what we might be able to do.

responder: Kevin K.  Replied July 31, 2024, 5:46 PM EDT
response: Thank you Anne for your question to "Ask Extension".  My first question is are the symptoms spreading?  If they are not spreading then it could be freeze damage from this past winter.  If it is spreading then there are a couple of diseases to look at.              The first to look at is Volutella blight.  Branches die back and leaves turn from green to light green-yellow and finally to shades of tan. Affected leaves turn up and lie close to the stem. Black streaks may be found on some petioles or on stems near petiole attachment. These symptoms are similar to winter injury, except that numerous, small, salmon-pink fungal spore-producing structures (sporodochia) appear on lower surfaces of affected leaves and branches. Diseased branches should be pruned out when the foliage is dry.  An important measure to help prevent and control Volutella is thinning (instead of shearing) boxwood to improve air circulation and light penetration. Thinning is a type of pruning that removes interior stems.  Old fallen leaves and diseased leaves that have accumulated in the crotches of branches in the interior of the plant should be shaken out and removed.      The other possibility is phytophthora crown and root rot. It is a fungal infection. Infected plants often show wilting, discolored or dead leaves which remain on the branches, dead twigs and branches, stunting, gradual decline, and premature plant death. Infected roots become watersoaked and rot. Streaking or dark staining may be observed when cuts are made into the wood near the crown of the plant, or cankers may be present on the crown. The fungus persists in the soil and in diseased plant material. Phytophthora prefers high soil moisture.  Do not replant boxwood in areas where it has died previously.  Remove and destroy infected plants, including roots where possible.  Your photo best matches this diagnosis.  There are no chemical controls.      I hope that you find this information useful and if you have additional questions you are welcome to respond.

responder: The Question Asker Replied August 08, 2024, 6:32 PM EDT
response: Hello Kevin,Apologies for the delay in responding to your informative and helpful message. There does not seem to be any spread of symptoms in our boxwood hedge and we have not seen any necrosis therefore we plan to proceed as though the problem is because of the freeze by carefully clearing out at least some of the dead material. There are already some new shoots appearing on some stems so that seems hopeful. Fingers crossed. Thank you for your message.  Anne      On Wed, Jul 31, 2024 at 2:46 PM Ask Extension <<personal data hidden>> wrote: