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.
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- Figure 1: Cold injury leading to individual and sections of branches of boxwoods dying back. Secondary infection by Volutella was confirmed by lab testing.
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- Figure 2: Tip damage due to cold temperatures
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- 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).
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- Figure 4: Individual boxwood branch showing symptoms of Volutella blight
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- 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:
https://ag.purdue.edu/department/btny/ppdl/
Selected References
Colletotrichum dieback
https://www.ncipmc.org/communications/pest-alerts/boxwood-dieback/
https://www.purduelandscapereport.org/article/other-boxwood-issues/
Boxwood Blight
https://www.purduelandscapereport.org/article/boxwood-blight-be-on-the-look-out/
https://purdueplantdoctor.com/factsheet/tree-404
Volutella Canker/Blight
https://purdueplantdoctor.com/factsheet/tree-91
https://www.purduelandscapereport.org/article/volutella-blight-and-dieback-of-boxwood/
