Stephen J. Toth, Jr. and Thomas A. Melton, editors

The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.

Date: September 27, 2001

From: Frank J. Louws, Extension Plant Pathologist

Over the last 3 days we have diagnosed anthracnose in several strawberry plug-production facilities. The problem does not appear to be restricted to one or a few operations but may be more widespread.

To date, we have characterized what appears to be the Colletotrichum acutatum strain. This strain is typically associated with the anthracnose fruit rot (Figure 1) and less commonly with plant collapse. In a plug production facility, the problem appears to start has hot spots. Plants in such hot spots show a general unthriftiness, remain stunted and are slightly discolored compared to neighboring symptomless plants. Such plants may resemble symptoms due to lack of water or high salts injury. As the disease progresses, one or more leaves wilt and the base of the leaf (petiole) becomes brown and wet (Figure 2 and Figure 3). Advanced stages of the disease result in plant collapse. Botrytis crown rot and Pythium or Rhizoctonia crown rot may have similar symptoms. Therefore, it is essential diseased plants are properly diagnosed. For the diagnostician, incubate infected tissue for 24 hours and observe for characteristic spores and fungal structures such as sterile setae. In some cases, we have isolated the pathogen.

If a grower has such a hotspot in the greenhouse, contact your local Cooperative Extension Agent and send samples to the Plant Disease and Insect Clinic according to the clinic instructions. Once it arrives there, I will diagnose the samples (do not send samples directly to me).

If anthracnose has been diagnosed, a suggested plan of action is outlined below:

1. Abandon the entire set of plants and find an alternative source of plants. It is difficult to determine how widespread the pathogen may be in the plug-production facility. It is common that plants may be infected but not showing symptoms yet. Such plants will remain stunted in the field, or die. If the plants do not die, there is a high risk of anthracnose fruit rot in the spring when warm wet weather occurs and if no treatments are applied. The spread of the pathogen is likely to be greater in facilities that use sprinkler systems (larger water droplet size) as compared to those that employ misting systems.

2. If an alternative source of plants is not a realistic option, immediately remove all infected trays and 1 to 2 sets of trays surrounding the infected area(s). Cull hard. Do not handle plants when wet and avoid touching healthy plants after handling suspected diseased plants. Minimize overhead watering.

Currently North Carolina has an active Section 18 for Quadris until October 15, 2001. In our work with anthracnose fruit rot management, the best results have been obtained by tank mixing captan (2 pounds per acre of active ingredient; e.g. 4 pounds of Captan 50WP) with Quadris (12.6 fluid ounces per acre). The higher rates are recommended for problem fields. For new plantings, add the fungicides in 100 gallons and apply the products in a directed spray over plants until run-off. In other words, add the fungicides at the above rates in 100 gallons of water and apply the necessary amount of water to get good coverage. This reduces the amount of fungicide needed per acre. Use a high-pressure sprayer to penetrate into the plants. Apply one application ASAP after planting and a second application on or just before October 15, 2001. Captan can be used in subsequent applications until the weather cools and danger of disease spread decreases. An aggressive fungicide program can be initiated again in the spring pending the registration of Quadris or similar product. A current Quadris label is available at the Berry Agent website or the North Carolina State University Pest Alert website.

Anthracnose in transplants occurred in 1999 and photographs of February/March symptoms have been posted at alert13.html. To date, the plants with symptoms in plug-production facilities have been restricted to one or a few hot spots. In such cases, there is some optimism the problem can be contained and plan #2 as outlined above may minimize losses. However, there is a risk that the disease is more widespread in plants than is apparent and plan #1 is a better option.

If you have further questions or concerns, please contact Dr. Frank Louws (telephone: 919-515-6689; e-mail: frank_louws@ncsu.edu).

Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Last modified on September 28, 2001 by Stephen J. Toth, Jr.