Thursday, August 23, 2012

Plant Carbuncles: Anthracnose on Banana Peppers

Anthracnose on banana pepper (Photo: L. Kaderabek)
We recently received banana peppers that were covered with sunken dead spots. The lesions on the fruit are symptoms of a serious fungal disease caused by Colletotrichum acutatum, C. coccodes and other Colletotrichum species. Lesions can also be found on stems and leaves. Colletotrichum acutatum produces pink spores in a sticky matrix, which often appears to coat the lesions in pink or salmon-colored ooze. If you look at the lesions with a hand lens, you can see small black dots arranged in concentric rings. These are fruiting bodies that produce the spores. The name of this disease is anthracnose.
Anthracnose lesions: Note salmon colored spores (Photo: L. Kaderabek)
Anthracnose lesions: Note concentric rings and black fruiting bodies (Photo: L. Kaderabek)
Several common plant diseases are called “anthracnose.” Unlike other tongue-twisting plant disease names, the “anthracnose” does not come from the name of the pathogen that causes it. Rather, it describes a disease with characteristic sunken lesions like those we saw on the pepper. This description is not very evident until we look at the Greek roots of the word “anthracnose.” It is derived from anthrax (carbuncle) + nosos (disease). Carbuncles are large boils – think of the Summoner in Canterbury Tales, who Chaucer describes as having a face covered with carbuncles, or of Prince Charles referring to a building proposed for a historic part of London as a “ . . . monstrous carbuncle on the face of a much-loved and elegant friend.”

Anthracnose on pepper usually begins in “hotspots” in a field. The disease is favored by warm, wet weather. Because the masses of spores produced on the oozing lesions are perfectly adapted for dispersal in splashing rain or irrigation water, periods of rainy weather can lead to rapid spread and devastating losses.

The pathogen survives on plant debris left behind from previous plantings or on other susceptible plant hosts. Although the pathogen can survive on infested plant debris, typically it does not overwinter more than one year in the absence of a host, and rotation is an effective control. Peppers should be rotated out of infested fields or gardens for at least two years. Other hosts to avoid include tomatoes, eggplants, other solanaceous plants, and strawberries. The fungus can be introduced from contaminated seed, so always start with disease-free plants and seed. Removing infected fruit early in the season reduces inoculum levels. After harvest, disk or cultivate to bury debris. All infected fruit should be removed and buried. Left over plant debris from hotspots should also be removed to reduce inoculum levels.
Strawberry Anthracnose: Note salmon colored spores (Photo: E. Lookabaugh)
Strawberry Anthracnose: Note red marbling of the crown (Photo: E. Lookabaugh)
Resistance is available in some varieties of chili peppers, but not in bell peppers. Choose varieties with shorter ripening periods since the longer the fruit remains on the plant, the more likely it is to become infected. Once disease develops, anthracnose is very difficult to control. Fungicide applications should be used preventatively (at time of flowering) in fields with a history of anthracnose. For chemical control recommendations, click here