More information about the 2013 strawberry virus outbreak

Many of you probably have seen an article in today's Raleigh News and Observer about virus problems in this year's strawberry crop. The Plant Disease and Insect Clinic has received several strawberry samples with virus problems in the past few months.

Here are some comments from Dr. Frank Louws, Extension Specialist for Strawberry Diseases in NCSU's Department of Plant Pathology about the strawberry virus situation:

This link will take you to an excellent article from Dr. Chuck Johnson at Virginia Tech about this year's strawberry virus outbreak. All the information for Virginia is true for NC and other states with this problem. The main question growers ask is: “What can we expect in yields?”. We have only limited experience with these viruses in our annual systems. However, we had a case of Strawberry Mild Yellow Edge Virus (SMYEV) in 2004, as shown below in Sweet Charlie plants photographed at full harvest. About 25 to 30% of the plants were affected by the virus and the virus dramatically affected plant growth and yield, as seen in the picture. This year, two viruses, SMYEV and Strawberry Mottle Virus (SMoV), have been diagnosed from problem fields. We do not know how these viruses will affect crop yields in 2013, but some reductions are expected. Specific recommendations for dealing with this problem can be found in Dr. Johnson’s article. With good management, this problem should not recur in future years. 

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