Tuesday, July 19, 2011

Blueberry Necrotic Ring Blotch

Blueberry necrotic ring blotch symptoms were evident in some 'Star' fields visited this week.  The cause of this disorder is unknown, but a virus is suspected.  It seems likely that this disease was introduced, and is spreading, via propagation from infected plants.

Symptoms are round to irregular, brown to black spots or blotches.  Unlike the rings caused by blueberry red ringspot virus, these rings are visible on both the upper and lower surfaces of the leaf, as shown above.  As with other leaf diseases, affected bushes tend to drop leaves earlier in the fall of the year, and this can translate to fewer flower buds the following year.

Symptoms usually appear on the oldest leaves first, with younger leaves progressively less affected. These leaf spots might be confused with fungal leaf diseases, but unlike fungal spots that have dead centers, most of these spots remain green in the center.

There are no control measures known for this disease, although some cultivars are more affected than others. Cultivars most affected include V-1, Star and O'Neal. The disease is present in Florida, Georgia, North Carolina and South Carolina.  The vector, if any, is unknown.

Growers should be advised not to propagate from visibly infected bushes, and to buy plants from tissue culture or other sources known to be free of symptoms.