Tuesday, September 27, 2011

Cylindrocladium blight

Cylindrocladium blight is a disease caused by a plant pathogenic fungus.  Infection results in leaf spots, brown, dead stems, and often dead plants.  On blueberry it is a disease of propagation and nursery beds, and is rarely seen on plants in the field. Symptoms commonly appear in blueberry rooting beds in the late summer and into fall. The disease may also occur in potted plants that are spaced too close together in pot yards.  One species of this particular fungus also infects peanut plants in the field, so blueberry propagators in North Carolina often call the disease "peanut blight".  There are many species of Cylindrocladium that infect plants, and there may be more than one species of this fungus causing disease in blueberry rooting beds.  At present the only species reported on blueberry in North Carolina is now considered to be Cylindrocladium parasiticum, hence the common name of the disease, Cylindrocladium blight.

Cylindrocladium blight in a bed of softwood cuttings in late fall.

Closeup of orange fungal fruiting bodies on an infected cutting

Irregular-shaped spots on lower leaves of older rooted cuttings

The disease is most often seen in propagation beds and pot yards that have grown vigorously and are too dense to allow proper air movement between plants.  Spores of the fungus infect leaves and stems, and eventually kill entire plants.  Often the root system is the last healthy part remaining.  The phenomenon of plants dying in the center of a dense block, while those at the edge (with better air circulation) survive, is characteristic of this disease in dense beds of plants.

Large area of dead plants in a propagation bed late in the season

In pot yards and late-stage propagation beds where the plants have already formed roots, this disease is best managed by not over-watering or over-fertilizing plants, and by maintaining proper plant spacing so that the leaves and stems can dry between waterings.  Cull to remove and discard any dead plants, and space the remaining plants out as much as possible so that there is good air movement between the bushes.  Do not re-use any old used potting media, as this disease can carry over from one year to the next in contaminated soil or potting mix.  Clean up as much debris as possible and sanitize the bed area and any pots that you plan to re-use.