Boxwood Blight Information for Homeowners and Landscapers

(Calonectria pseudonaviculata)

Homeowners, Landscapes and Gardens

The following is a short list of Best Management Practices (BMPs) to avoid/mitigate Boxwood Blight in a home garden or commercial landscape.

• Only receive boxwood from reputable sources.

• Mulch at least 1” every year, but with a thin application after initial mulching.

• Avoid transient landscape contractors and mowers who work in other boxwood gardens.

• When planting a site, old or new, consider these factors before planting boxwood.

  • Is Boxwood Blight pathogen already on site from previous planting?  If so, other BMP’s must be strictly adhered to for the boxwood garden to succeed, regardless of the cultivar used.

  • Avoid sites where air movement is blocked by other buildings/ plants/ flowers/ trees. 

  • Heavy shading and slow drying areas are more conducive to Boxwood Blight.

• Avoid more susceptible cultivars when replanting.

• If Boxwood Blight shows up, follow Best Management Practices to quickly and decisively stop the infection.

• Minimize any overhead irrigation.

• Apply fungicides to highest risk plants if resources are available.

• If severe outbreak of Boxwood Blight occurs, and site lacks proper air movement, consider other options.

Homeowners, Landscapes and Gardens

Landscapes and gardens are different from nurseries in that they are the end-user of nursery plants.  For a plant to live indefinitely in a garden, it does not have to be perfect, but it must be attractive.  Therefore, a slightly blemished plant might be in a garden for many, many years if it continues to have the WOW Factor.  While nurseries have zero tolerance for Boxwood Blight, perhaps a small amount is okay in a landscape if it does not take away from the overall looks of a plant.  To spray boxwood in a garden every two weeks throughout warm weather would be an expensive and time-consuming exercise.  A goal of a gardener might be to spray a boxwood just enough that Boxwood Blight does not defoliate a significant amount of the foliage.

Obtain the latest fungicide recommendations from your state Cooperative Extension service.

TIMING

If a garden has susceptible cultivars, a gardener should consider an abbreviated fungicide spray schedule.  Depending on weather pressure, a spray schedule of once a month during the highest-pressure periods would greatly reduce symptoms of Boxwood Blight.  A schedule such as this has proved to be very effective, particularly if there are minimal infected plants in the area.  A gardener should consider increasing the frequency of the sprays under conducive weather patterns and discovery of spread of Boxwood Blight.  They should also consider decreasing the frequency of sprays during periods of weather conditions unfavorable to the disease.

Fungicide applications should begin in the spring when conditions become favorable for infection. The residual activity of fungicides is affected by amount of rainfall, weathering, and degradation, and they must be reapplied at regular intervals while the risk of blight infection is present. However, they must not be applied more frequently than recommended treatment intervals or applied at higher rates than specified on the product label. Always read and follow product labels for safety instructions regarding mixing, handling, compatibility with other chemicals, application methods, re-entry intervals and limitations on amounts of product per acre per year.

EQUIPMENT

Because blight spores can stick to tools, equipment, spray hoses, etc., sanitize all equipment, shoes, gloves, etc., used in tending and treating boxwood to prevent spread of fungal inoculum to healthy plantings. For a list of sanitizer recommendations, refer to the Boxwood Blight Task Force website. It is recommended that vehicles that may have been exposed to the Boxwood Blight fungus be thoroughly washed of debris (e.g. cleaned at a car wash) to avoid spreading the fungus from one planting to another.

To be noted: While Saunders Genetics has worked with nursery growers who have successfully used the pesticides listed above, no guarantees or promises, nor any opinions concerning the effectiveness or safety of these or any other pesticides are made.  Always read the labels and other product information from the manufacturer and discuss the proper use and application of products with appropriate company representatives or acknowledged experts.

If suspected:

• Take samples to testing labs and limit access to area until results are obtained.

If confirmed:

• Take great care not to further spread disease.

• Do cleanup on dry, sunny days when foliage is dry.

• Consider fungicide applications before and during cleanup to control spread.

• Wear rubber boots and disposable clothing during cleanup to lessen contamination of clothing and shoes.

• Cut and place the infected plants in a plastic bag and take care to catch as much leaf litter as possible.

• Clean up as much leaf debris as possible. Roots are not believed to carry Boxwood Blight.           

• Debris should be burned or taken to landfill with care not to let leaves escape.

• After cleanup, wash skin, launder or dispose of outer clothing, and wash boots.

• Increase airflow in and around remaining plants by thinning and removing lowest limbs.

• Try not to allow any debris to be buried as the disease can survive in the soil for long periods of time.

• All tools and equipment should be thoroughly cleaned when moved between different gardens or areas.

• Mulch to lessen the splashing of spores.

• Monitor boxwood in times of optimal conditions for new infections and flare-ups.

• If severe outbreak of Boxwood Blight occurs on a site that lacks proper air movement, considers other options.

If you suspect the disease in the landscape, you should take great care in collecting samples by double bagging them and taking them to the local Extension office or another testing lab. The area should be roped off or temporarily fenced off until the results are obtained.

If Boxwood Blight is confirmed, you must be diligent and careful in cleanup. Extreme care should be taken to avoid infecting other plants with debris or plant contact. Choose a time to cleanup when it is sunny and when foliage is dry. Again, the plant is less likely to be sporulating when foliage is dry. Consider applying fungicides to any area where you are working to kill any spores that might be present.

Always wear some sort of disposable suit, like disposable Tyvek® coveralls. Also, wear rubber boots as they can easily be cleaned. If possible, put a plastic bag over the infected plant and cut the plant off at the base. Take care to catch as much leaf litter as possible. Then, clean up any leaves that fall before disturbing the soil as you do not want to incorporate diseased debris into the soil. After all debris is cleaned up, remove the roots. All debris should be bagged or covered to eliminate the possibility of it blowing or falling out. Do not compost the debris. Burning the debris is the best option when possible.

After the cleanup is complete, remove outer clothing and launder or dispose of it. Laundering with detergent and hot water will kill spores. Boots should be thoroughly washed, and all tools and equipment should be carefully cleaned as well. Prune any other boxwood in the landscape to increase airflow to maintain dry foliage. Remove any limbs that touch the ground and might get rain splash, and be sure plants are properly mulched. Continue to monitor any boxwood during environmental conditions conducive to infection.

Since 2011 when Boxwood Blight was first discovered in the United States, there has been a great deal of research and much has been learned regarding control and living with the disease. The early assumption was that any landscape that is infected by Boxwood Blight would need to be destroyed. If the landscape is primarily Buxus ‘Suffruticosa’ (English), which is very susceptible to Boxwood Blight, then that would likely be true. At a minimum one should remove any plants in the vicinity of the infected plant(s) and closely monitor all other plants. However, there are landscapes of Buxus sempervirens (American), which have medium resistance to Boxwood Blight, which can survive and even thrive if certain steps are taken. Remove the diseased sections, prune to increase air movement within the plant, remove lower limbs, and mulch to lessen splashing of spores from the ground. In addition, the plants should be carefully monitored when infection is likely. A few well-timed sprays would also increase the chances of success.