Our boxwood plants seem to be suffering…brown leaves, sparse foliage this spring. I see others in the neighbourhood like this. Ours sit close to the house in a west facing garden, sun/partial sun situation. This is a mature plant approx 36″ wide and 44″ high. Is this just winter burn? I don’t see anything alive on it at this time. What would you suggest?
Thank you for contacting the Toronto Master Gardeners concerning your boxwoods.
Boxwoods are plaqued by a number of environmental issues as well as a number of pests and diseases. They may suffer due to cold winter injury and salt damage, fungal diseases, pests, incorrect soil, poor drainage, poor nutrition, or periods of drought. Any one of these issues alone or in combination can be detrimental. It is difficult to pinpoint from your photo what is causing the problem with your boxwoods. Did you notice any dying, browning leaves last summer or has this issue just appeared? Perhaps, salt was coming off your porch in winter?
It could be that your boxwood have succumbed to one or more of the following pests and diseases: boxwood blight, box tree moth, boxwood spider mite, boxwood leaf miners and boxwood psyllid.
We have numerous posts on our website concerning boxwood and their diseases. Simply type Boxwood into the Find it Here bar located to the right of the page.
The following information on the above pests are from some of our archived posts:
“Boxwood blight is an emerging fungal disease that was first identified in England in 1994 and has since spread through Europe, Asia and New Zealand. It was detected in the US in 2011 and in Ontario in 2014. The spread is attributed to the inadvertent transport of infected nursery stock. The symptoms are circular leaf spots with dark margins and black-brown streaking on stems. As the disease progresses the leaves will drop till the plant is completely defoliated.
The roots of the plant are not affected so if the fungus is detected early you may be able to save an infected plant by removing the diseased portions. Be sure to disinfect your tools after working with diseased plant material and avoid working with healthy plants after dealing with the diseased ones as the sticky fungal spores can adhere to your clothing and other equipment. Otherwise, diseased plants should be removed and sent to landfill. Never compost diseased plants or leaf debris or include in municipal garden waste.
If you wish to replace the diseased plants, be sure to select a resistant variety. One of the most resistant varieties is a hybrid developed in Canada called the ‘Green’ series with cultivars such as Green Gem, Green Mountain and Green Velvet. You should find these cultivars readily available in local nurseries. Landscape Ontario, the professional association for the horticultural trades has been very active with their members to ensure nursery stock is free of the fungus.
The fungus favours warm, humid weather and shady conditions. So creating a less conducive environment will help to reduce the spread and severity of the disease. The following practices are recommended:
- Plant in full sun and prune overstorey plants to allow lots of sun to penetrate through to the leaves which will reduce the time the leaves remain wet after rain.
- Mulch around the boxwood to reduce the splash of overwintering spores that may be present in fallen leaf debris.
- Avoid overhead watering to reduce splashing and leaf wetness.
- Keep space between plants to maximize air circulation.
- Rake up any leaf debris.”
For further reading, particularly on the prevention of blight, and plant management, please see this tract published by Landscape Ontario and Perdue Extension Research.
“Boxwood Leafminer (Monarthropalpus flavus), is the larva (immature form) of a small, orangish mosquito-like fly. Here is a link to a previous Toronto Master Gardener posts on ‘time to deal with boxwood leaf miners’, which you may find informative: Boxwood leafminer, Boxwood Shrubs Infested“
Have you noticed any signs of fine web material, or droppings, of the box tree moth larvae. The BTM is an invasive pest also capable of causing severe damage — leaves are ‘skeletonized’ by the chewing larvae — to plants in Ontario, and particularly during seasons following mild winters, resulting in high levels of eggs hatching. If this was the case, yes, boxwood leaves could be sprayed mid-May (and again, when the next set of eggs hatch, in the summer), with a biological insecticide containing a naturally occurring bacterium, Bacillus thuringiensis (B.tk), which causes the caterpillars to become ill after feeding on sprayed foliage.
“The horticultural association for landscape professionals, Landscape Ontario, has been monitoring and controlling the spread of box tree moth in Toronto for several years. Box tree moth larvae can be effectively managed with a safe biological insecticide – registered for use in Canada. If you identify the caterpillars eating your boxwood in May contact Landscape Ontario promptly. They can advise you on managing box tree moth and refer you to a professional to administer the insecticide. For more information https://horttrades.com/rejuvenating-boxwood-plants-damaged-by-box-tree-moth “
Enrich the soil around the plants with compost in the spring to add nutrition and improve the soil structure, thus allowing better water absorption. Do not overfertilize. Carefully clean up of any leaf debris from around the plant.
As the spring progresses, check for new buds. Once they start developing, you can cut back any damaged or dead branches. You may want to thin the plants lightly to permit better air circulation.
Avoid pruning boxwoods in the late summer or fall as this spurs new growth which won’t have time to harden off before winter and be killed by the cold. Also, avoid pruning boxwoods on very hot days. Make sure to sterilize any shears or clippers used to prune or trim all garden plants by soaking in bleach: water solution (diluted 1:9) or rubbing alcohol for 10 seconds
Water new boxwoods regularly with a deep soaking to keep the soil around the plant moist, but not soggy. Once established, boxwood plants will only require watering during drought periods. However, if the plants are close to the house under the roof overhang, they may not receive sufficient water from rain, and may need regular ongoing watering.
In the fall, make sure they get watered until the ground freezes. This is especially important in our South Central Ontario region where the ground can still be frozen on sunny days. When this happens the plant foliage starts to transpire, but the roots cannot replace the lost moisture from the frozen soil, so the foliage dies of dehydration.
Lastly, this link on Boxwood alternative will provide alternatives to your boxwood should you decide to replace them.
Good Luck with your boxwoods.