Viburnum dentatum, common name arrowwood, is a deciduous shrub that produces small, white clusters or flowers and dark blue fruit. In fall, the leaves turn reddish-purple before falling. This plant will grow from 6 to 12 feet and is fairly hardy, preferring well-drained, slightly acidic soils but tolerating damp ones if necessary.
While Viburnum dentatum tend to be fairly low maintenance, there are a few diseases that can kill these plants if proper steps are not taken to treat them. The best way to keep your arrowwood plant healthy is to know the signs and symptoms of Viburnum dentatum diseases so you can avert any trouble before it becomes a serious risk to the plant.
Gray mold attacks many deciduous plants, including Viburnum dentatum. This mold, also called botrytis, lives on dead and decaying plant materials and can move from dead debris to a live host. If your Viburnum dentatum has gray mold, you may notice a gray or black substance coating the leaves or flowers, or you may first start to notice leaf yellowing and fall if the mold has attacked the roots or the stems of the plant.
Use sterile pruning techniques to remove all affected areas of the plant, then clear the area under the plant of all plant debris so the fungus cannot reinfect the plant via infected dead material. Water your arrowwood plant using a drip hose to prevent splashing, which spreads the fungus, and water early in the morning to avoid creating a humid environment around the plant. If the botrytis returns, you may want to complement your efforts with a fungicide.
According the University of Illinois Extension, verticillium wilt is often confused with root rot because the leaves yellow and fall prematurely and tend to appear wilted even when the plant has plenty of water available. The best way to diagnose verticillium is to check the exterior wood on your arrowwood. If the wood is stained a dark, olive-green, then your plant has verticillium wilt, not root rot.
Prune (sterilizing the tool between cuts) to remove all affected areas of your Viburnum dentatum, then fertilize the plant with a fertilizer that is low in nitrogen and high in potassium. Remove all plant debris from the area to prevent reinfection. If the infection was not severe, your plant may recover. If the infection returns you will need to remove the entire plant before the wilt infects plants in the surrounding area.
Cankers and Dieback
Given the opportunity, canker infections will kill a Viburnum dentatum plant by girdling its twigs and branches, then finally invading the stem. Cankers are hard to spot early in the infection because they tend to be moderately discolored depressions on the wood of the plant. As the infection worsens, you will notice swollen bulges on the sides of the plant and the foliage on the plant will turn brown in these areas.
Remove affected limbs of the arrowwood several inches below where the canker has formed. Use sterile pruning techniques and do not drop the debris on the ground, where it can reinfect the plant. You can complement your efforts with a fungicide to prevent reinfection, but removal of infected materials should resolve the issue as long as you are able to remove all of the fungal-spore infected areas from the plant.