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You have box trees, you have problems? – Washington Daily News

You have box trees, you have problems?

Posted at 12:09 p.m. on Friday, October 28, 2022

I’ve been in and out of town for the past few weeks with talks, workshops, and trainings. This is my chance to learn from other professionals in the disciplines of horticulture, entomology, pathology and weed control. Horticulture in general covers so many areas that it is really hard to know everything and this is our chance as industry professionals, academics and educators to come together and share.

Over the past week, I have learned several new disease and insect issues to watch out for. Things that might be on the way like the Asian longhorned beetle or the spotted lanternfly or are already there that I may have misdiagnosed as boxwood dieback.

The Asian longhorned beetle is a pest mainly concentrated in the northern states. However, a population has been confirmed in Charleston County, South Carolina in 2020. It occurs on multiple hosts, from maples to mimosa. The adults burrow into the bark of the tree to lay their eggs which hatch into a larva up to 2 inches long. The larvae burrow into the phloem of the tree and then move to the xylem to feed until pupation. They will reappear as adults to complete the life cycle. The feeding galleries dug by the larvae are quite wide and destructive because they structurally weaken the tree. Feeding also cuts off the flow of water and nutrition to the leaves.

I think we’ve all heard of the spotted lanternfly. This pest has been around for a few years now, even catching the attention of Saturday Night Live a few weeks ago. The update is that there are now populations in two North Carolina counties and several isolated adults have been found across the state. This pest is largely aesthetic but can be detrimental to our vineyards.

Boxwood dieback is another problem to observe on boxwood trees. It is very similar to phytophthora root rot in that it will appear as yellow clumps of leaves scattered among the foliage. After uprooting and inspecting the roots, they look healthy. The next diagnostic step is to look for stem and/or vascular streaks in branches that are discolored. There is no control for this disease after withdrawal. When trimming the hedge, disinfect tools between individual plants. Do not use your leaf blower to clean up pruning debris. This is a fungal pathogen that spreads by contact (leaf to leaf) and spores, using the blower and not sanitizing your pruning tools will ensure the disease spreads to other plants .

In addition to Phytophthora root rot, there are several other lookalikes on boxwood trees that can cause similar symptoms. Boxwood blight is probably the best known of these. There have been known cases of this pathogen statewide since 2011. Leaf spots and lesions can be seen in the lower canopy, usually circular in shape and having a dark border with a light brown to purple center. Leaves will begin to turn yellow or tan and may have sticky gray to white fungal spores on the underside of the leaf during hot, humid conditions. On the stems, black lesions or streaks will be present. Symptoms are often noticed on the shady side of the plant at first, then defoliation occurs throughout the plant. This is a major issue because it affects several species of boxwood.

Volutella blight is another problem that can afflict our box trees. This is a very similar problem to boxwood blight and can be the initial or secondary pathogen of boxwood blight. More leaves will remain on the plant than with boxwood blight. Checking the underside of the light green to brown leaves, you will see salmon-colored spores.

Finally, boxwood leafminers may exhibit leaf spots that resemble those of boxwood dieback and these other lookalikes. Leaf miners penetrate between the layers of leaf tissue to lay their eggs. Eggs hatch and larvae feed on leaf tissue before pupating and emerging as adults the following spring. Leaves turn yellow and defoliate with a puffy appearance.

So, with all this, why plant boxwood? They are usually very easy to manage in well-drained soil and ideal conditions. However, we often expect our boxwoods to live in far less than ideal conditions. I think a lot of our problems are the result of cultural management errors. Knowing the particular culture of a plant can go a long way in keeping it healthy. To learn more about the plants you have in your landscapes, or to research plants before planting, visit our Gardener’s Extension Plant Toolkit at plants.ces.ncsu.edu.

If you are having difficulty growing in your home environment, call the extension office at (252) 946-0111 or email me at [email protected] If you have a plant you can’t identify or want to learn more about the plants in your landscape, let’s talk! As a former family doctor, I make house calls if we cannot figure out your problem.