From BASF: The Chemical Company Website

By Paul Pilon

The fungal pathogen Cylindrocladium can be a very devastating disease.  It is one of the lesser known pathogens of ornamentals.  This disease attacks woody plants more frequently than herbaceous plants. Several ornamental and greenhouse crops which are susceptible to Cylindrocladium include Azalea, Baptisia, Camellia, Lupine, Pelargonium, Peony, Rhododendron, Roses and Spathiphyllum to name a few.  This pathogen most commonly causes cutting rot, crown rot, and root rot.

Box Blight Most recently outbreaks of 'box blight' caused by Cylindrocladium pseudonaviculatum (Cylindrocladium buxicola) have demonstrated how severe this pathogen can be. 'Box blight' or boxwood blight are the common names frequently used when referring to Cylindrocladium infections on Boxwood (Buxus spp.). 

Symptoms of box blight may appear as light to dark brown often circular spots with dark borders on leaves which may grow together to cover the entire leaf surfaces, black streaks or cankers on stems appearing at the bottom of the plant and moving on up, straw to bronze colored blighted foliage, and rapid defoliation.

The disease cycle for boxwood blight occurs very rapidly and can be completed in one week.  Infections most commonly occur with humid conditions with warm temperatures (64 - 77° F).  Cylindrocladium may still develop at lower temperature (> 50° F).  High humidity or free water on plant surfaces are necessary for infections to occur. Shady growing conditions also favor disease development.

Cylindrocladium can be a very difficult disease to control once symptoms are present. Fungicides can be used to prevent infections from occurring, but are not effective at controlling active infections (after moderate symptoms are present). Therefore, infected plants should be removed from the production site and destroyed.  After the infected pots are removed, it is recommended to begin applying fungicides to reduce the likelihood of future disease development.

For 'box blight', it is recommended to apply the tank mixture of pyraclostrobin + boscalid (18 oz/100 gals) plus chlorothalonil (or mancozeb).  After two consecutive applications rotate to the tank mixture of fludioxonil plus mancozeb (or chlorothalonil). 

Cylindrocladium in Ornamentals On ornamentals, there are a number of symptoms that can be expressed from Cylindrocladium infections. The primary symptoms are black or brown sunken lesions at the base of the stem, leaf spots, stunting, dead stems and leaves with little if any root damage, and cutting rot.

Similar to the environmental conditions required for boxwood blight, conditions that promote Cylindrocladium infections with ornamentals include using contaminated cuttings, excess water, poorly drained potting media, contaminated fields, reusing potting media, and reusing pots or flats from previously infected crops without thoroughly cleaning and disinfecting them.

Fungicides which provide good preventative control include those containing the active ingredients fludioxonil, iprodione, pyraclostrobin + boscalid, thiophanate-methyl, and triflumizole.

The mention of specific active ingredients does not constitute an endorsement or recommendation of, or discrimination against similar products not mentioned. ALWAYS READ PRODUCT LABELS AND USE THEM AS DIRECTED ON THE LABEL.