3/25/2014 - By Harrell's

Boxwood Blight has been documented in Europe for several years now  and has just started to take hold here in the US. The pathogen responsible for this blight is a strain of Cylindrocladium. Like many other leafspot diseases, the spores of this disease are spread via splashing water and on strong wind currents. Boxwood Blight can also be spread from an infected host plant to any cuttings that are taken. Control measures should begin as soon as Buxus is propagated or bought in. Boxwood cuttings are especially susceptible due to the fact that they are often in high humidity environments during the rooting stage. This disease is being furiously researched and we at Harrell’s are committed to working with our growers on this problem.

 Symptoms

• Brown to black lesions located on the upper surface of Buxus leaves. Disease usually first appears inside the heavy dense canopy of the plant, inspect the interior of the crop closely.  
• White mycelium growth will appear over time on the underside of the leaves.
• Black sunken cankers can be found near the leaf petiole on infected plant stock. This quickly progresses to leaf drop.
• In severe infections, complete plant defoliation can occur. In optimal growing conditions these symptoms can progress in as little as 7-10 days. Boxwood Blight will not actually kill its host plant, it simply will defoliate it. However this usually opens the door for  secondary pathogens such as Volutella blight to enter the host plant. Be sure to run a pathology test before applying fungicides!
• Roots of the plant will remain healthy looking. This can be used to rule out rot diseases such as Phytophthora or Pythium which will kill the host plant’s roots.

Current Recommended Chemical Control Options -

• Palladium – Fludioxonil & Cyprodinil – Group 12 & 9 – 6oz/100 gals
• Pageant – Pyraclostrobin & Boscalid – Group 7 & 11 – 18oz/100 gals
• Terraguard SC – Triflumizole – Group 3 – 8oz/100 gals
• Medallion – Fludioxonil – Group 12 – 4oz/100 gals
• Heritage – Azoxystrobin – Group 11 – 4oz/100 gals

Spray on 21 day rotations when temperatures are between 40-80°F. Reliable spray programs should be applied alongside sound Best Management Practice recommendations. (See attached pages) Controlling this disease in the nursery is going to be key to limiting its spread, once it gets into the landscape, control will be very difficult!

In addition to being one of the nation’s largest distributors of branded fungicides, herbicides and insecticides, Harrell’s produces top-quality, custom blended fertilizers, specialty liquids, and wetting agents for the golf course, sports turf, landscape management, and horticulture industries. Harrell’s guarantees stringent quality control procedures, tight manufacturing specifications and careful selection of raw materials for each product that carries the Harrell’s name.  They are also the exclusive eastern formulator and a leading world distributor of POLYON®, the industry’s superior controlled-release fertilizer technology.  www.harrells.com

Portions of this release are adapted from literature from NCState and UConn extension agency.