Is there anything that can be done to save boxwoods that were damaged from the winter weather? Is it a fungus? My boxwoods have large areas of browne...
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boxwood winter damage #843025
Asked July 28, 2023, 11:29 AM EDT
Is there anything that can be done to save boxwoods that were damaged from the winter weather? Is it a fungus? My boxwoods have large areas of browned leaves and it seems to be spreading. I also submitted a question re this to the non-landscape questions by mistake!
Thank you!
In the last five years, we have received 233 samples from Indiana, alone, with concerns ranging from boxwood leafminer to Volutella dieback and cold damage (Figure 1, 2, 3). Often, we find multiple problems on any given sample, and very frequently we see Volutella in association with dark cankers of stems that appear to have had some amount of cold injury earlier in the season. Figure 1: Cold injury leading to individual and sections of branches of boxwoods dying back. Secondary infection by Volutella was confirmed by lab testing. Figure 2: Tip damage due to cold temperatures Figure 3: Bark Splitting and sloughing due to cold injury on the stem
In 2023, we are on our way to seeing a record number of boxwood samples in the months of June and July compared to recent years, with the primary diagnosis being Volutella canker (Figure 4) and cold damage (see https://www.purduelandscapereport.org/article/cold-injury-during-a-very-mild-winter/). Joe Boggs has a great write-up of his observations, which mirror our own, for the state of boxwoods this year in the Ohio State University Buckeye Yard and Garden Line (https://bygl.osu.edu/index.php/node/2198).
Figure 4: Individual boxwood branch showing symptoms of Volutella blight Figure 5: Bare stems and stem dieback due to boxwood blight. Some leaf spots are present on the foliage, but there are a large number of stem lesions also visible on the plant.
We are also seeing an uptick in Colletotrichum Dieback samples, where symptoms of stem dieback look very similar to Volutella and winter injury. An important point to note is that with all of the issues mentioned above, the foliage is retained on the leaves for extended periods of time (but they do eventually fall off). Leaf spotting and leaf drop symptoms are more suggestive of boxwood blight (Figure 5). Many of the samples we have received were due to concerns about boxwood blight, caused by Calonectria pseudonaviculata, but there have only been two landscape cases of boxwood blight in the state.
This is encouraging, but we always recommend to evaluate any boxwood plants that you are intending to purchase for leaf spots, external stem lesions, and leaf drop. Along with our favorite mantras in the green industry, “Right Plant, Right Place,” comes “Start Clean, Stay Clean,” avoid purchasing any sickly plants, especially anything on the bargain or reduced-price shelves, since you do not want to bring anything unwanted home.
If you are concerned about leaf drop and suspect you may have boxwood blight, or have stem dieback issues in boxwood, and want help determining the cause of the problem, we recommend submitting a sample to the diagnostic lab. Please see our website below, or reach out via email:
One of the most common diseases found on boxwoods is Volutella blight and dieback, caused by the fungi Pseudonectria foliicola and P. buxi. Both fungi are considered weak pathogens, always around but not causing much damage until plants are injured or stressed, rarely infecting otherwise healthy plants. Volutella blight alone usually doesn’t kill boxwoods, but loss of branches can severely affect symmetry and ornamental value. A previous PLR article discusses Volutella blight on pachysandra.
Figure 1. Boxwood showing stunting and gray green color typical of early stages of Volutella dieback.Figure 2. Boxwood with Volutella dieback.Figure 3. Dead boxwood stems with a tan to straw color are often associated with Volutella dieback.
Symptoms and signs: During the growing season, infected branches may show stunted growth that later turns gray-green (Fig. 1) and usually dies by fall or winter (Fig. 2), becoming light tan or straw colored in spring (Fig. 3). A closer examination of stems may show bark splitting (Fig. 4) and/or sunken cankers at the soil line or in the crotches of branches where dead leaves accumulate. Wood under the sunken canker is usually blackened and the bark on blighted stems often becomes loose and falls away, especially on larger branches. The fungus produces clusters of fungal spores which are pink to cream-colored on lower leaf surfaces (Fig 5.). On blighted stems, signs of the fungus appear as cushions of small, salmon-colored spore masses that erupt through the epidermis (Fig. 6). Winter injury causes foliar symptoms similar to those caused by Volutella blight but without signs of fungal infection, and Volutella infection often follows winter or frost injury, leading to confusion about diagnosis. If dieback or bronzing is caused by winter injury alone, the plant should produce new healthy leaves later in spring and eventually hide the damaged leaves.
Figure 4. Splitting bark on a boxwood stem due to Volutella dieback and/or winter injury.Figure 5. Boxwood leaf showing sporulation of a Pseudonectria sp.Figure 6. Close view of Pseudonectria sp. sporulation on a boxwood stem.
Management:
Choose a well-drained planting site
Maintain plant vigor with moderate fertilization, taking care to avoid fertilizing after mid-summer to ensure good winter dormancy
Irrigate as needed during dry periods
Prune out infected branches back to healthy tissue and destroy all pruned material
Fungicides are not recommended for the control of this disease in the landscape
There are no resistant boxwoods available.
Other sources that may help are listed below.
Other Boxwood Diseases: Be aware that other disease problems, such as Phytophthora root rot or nematodes, can also cause loss of foliage and dieback symptoms on boxwood. Boxwood leaves that die as a result of Volutella, various root diseases or environmental stresses are frequently colonized by the fungus Macrophoma. This fungus produces numerous black fruiting bodies, which can be seen as dark specks on dead leaves. It is a secondary colonizer of dead leaves and its presence indicates that the plant is stressed by some other factor.
