From: Frank Louws, Assistant Professor, Department of Plant Pathology, NCSU
During the last week I have received numerous plant samples and visited field sites with anthracnose crown rot. Symptoms include stunted and dying plants. We have seen a unique symptom of brown margins around the leaves. When affected plants are pulled and the crown cut longitudinally, internal crown symptoms include brown discoloration along the vascular tissue, especially at the top (apical) portion of the crown. As the disease progresses, much of the top portion of the crown acquires a red-brown discoloration. This year we also have seen considerable Botrytis crown rot but this pathogen incites different symptoms. With Botrytis, plants will collapse but death is due to Botrytis infection of the leaf petioles and rarely do symptoms progress very far into the crown. If Botrytis crown rot develops includes signs of the pathogen such as gray masses of spores and mycelium, and the crown symptoms are more of a black-gray color, rather than red.
Isolation attempts have shown that both Colletotrichum gloeosporioides and C. acutatum are associated with symptomatic plants. The C. acutatum pathogen is of grave concern because it is very aggressive and will cause fruit rot under favorable weather conditions. Samples received and fields visited to date originate from one plant (plug) source (this does not constitute a confirmation that there has been any negligence or responsibility for the problem on behalf of this plant source).
Because the acutatum species is present, there is a high risk of
fruit rot in problem fields. No efficacious materials are currently
available, although in our trials, a weekly captan program provided
a marketable yield of 60% compared to losses of up to 75% in
non-sprayed plots. Therefore, growers with problem fields should
adopt a calendar-based spray program of captan of 2-3 lbs active
ingredient per acre on a 7 day schedule. In some cases, we have
seen the problem associated with Camarosa plants. If your clientele
has infected Camarosa plants beside an apparently healthy field,
your client is best advised to completely remove the infected
plants. The plants must be removed from the field. Killing the
plants with a herbicide will initiate spore production by the
pathogen and if plants are not removed the problem will be
aggravated. If you have a field that may have anthracnose, please
send samples to the Plant disease and Insect Clinic. Infected
plants have shown symptoms not seen before and we need to try and
characterize the pathogen and disease complex. If you have any
further questions or concerns, please contact Dr. Frank Louws
(919-515-6689; frank_louws@ncsu.edu). This notice is also posted to
the WWW at "alert13.html" where
pictures are available.
Web page last updated on March 31, 1999 by Stephen J. Toth, Jr..
