New Service Announcement: Testing Blueberry Fruit for Fungicide-Resistant Anthracnose (Colletotrichum species)

Anthracnose fruit rot, caused by Colletotrichum species, is a major disease affecting blueberries in Georgia and throughout the Southeast. Anthracnose fruit rot (also called ripe rot) is primarily managed in conventional production using chemical controls (fungicides) and good cultural practices, including timely harvesting and handling of ripe fruit, sanitation, and the removal of infected fruit from the field or harvest container. The application of fungicides from several different FRAC groups (representing different modes of action) is recommended to control anthracnose and prevent fungicide resistance development. Nonetheless, over time, with repeated fungicide applications, the pathogen population can develop fungicide resistance. If a significant portion of the pathogen population develops resistance in a particular area, fungicides may no longer be as effective as they were previously.

Ongoing fungicide sensitivity studies being conducted by Dr. Jonathan Oliver (UGA Fruit Pathologist) and recent fungicide resistance screenings carried out in the UGA-Tifton Plant Molecular Diagnostics Laboratory (MDL), have shown that some isolates of Colletotrichum from blueberry in Georgia possess resistance or reduced sensitivity to many of the most common fungicides used by Georgia blueberry growers for anthracnose control. To provide Georgia blueberry growers with information about the fungicide resistance situation in their particular fields, a screening test was developed and optimized during the 2026 growing season to allow for routine in vitro (laboratory) fungicide sensitivity testing of Colletotrichum isolates from blueberry. This test will be offered as a service to Georgia blueberry growers by the UGA-Tifton Plant Molecular Diagnostics Laboratory during the upcoming growing season.

This screening test evaluates the growth of Colletotrichum in the presence of the following fungicides (technical grade, 99-100% purity): pyraclostrobin, boscalid, fludioxonil, pydiflumetofen, fluazinam, cyprodinil, metconazole and penthiopyrad. These fungicides are the active ingredients in frequently used blueberry fungicide products including Pristine® [pyraclostrobin+boscalid], Omega® [fluazinam], Miravis® Prime [fludioxonil+pydiflumetofen], Switch® [fludioxonil+cyprodinil], Quash® [metconazole] and Fontelis® [penthiopyrad].

Using Colletotrichum isolates from infected fruit, fungicide-containing laboratory media (in 24-well plates) is inoculated and fungal growth is observed over several days. Fungal growth of each isolate in each media well is rated using a scale from 0-2.  (0 = No Growth; 1 = Minimal Growth; and 2 = The well is fully covered with fungal mycelia.) Based on the relative growth of each fungal isolate on a particular fungicide, the presence or absence of fungicide resistance is determined.

This testing service will be available to Georgia blueberry growers during the 2027 growing season. Testing will cost $200 per sample and this cost includes isolation and testing of five Colletotrichum isolates from each individual submitted sample. Instructions for sample submission are provided below:

Sample Collection and Submission Instructions:

1. Collect a representative sample(s) that represents the symptoms and signs of fungal infection (rot) observed. (Fruit samples should be freshly collected. Submit a generous number of symptomatic fruit, preferably with visible orange spores [conidia]. Do not send dried fruit.)
2. Place the sample in a plastic zipper bag, seal, and maintain samples fresh or refrigerated after collection until they are submitted to the MDL. Do not wrap the fruit sample in paper towels.
3. Label each sample clearly. Do not mix samples from different plant species in the same submission bag.
4. Complete the sample submission form.
5. If samples are hand-delivered directly to the laboratory in Tifton, they can be sealed in plastic bags as described above. Alternatively, place the samples in a box and mail them to the MDL. Do not send samples in envelopes.
6. Use the next-day or two-day shipping option for sending samples. It is important that the sample arrive within 48 hours of collection. All samples must be accompanied by a completed sample submission form. Mail samples early in the week to avoid the weekend layover in the post office.
7. A fee of $200 per sample will be charged (invoice) once the test is completed.

For more information or questions about the fungicide resistance screening assay, please contact the UGA-Tifton Plant Molecular Diagnostic Laboratory Director, Dr. Alejandra Jimenez Madrid, at a.jimenez@uga.edu.

Plant Molecular Diagnostic Lab website: https://site.caes.uga.edu/mdl/

For additional questions regarding fungicide use recommendations for anthracnose fruit rot control in blueberry, please contact your local agriculture and natural resources extension agent (https://extension.uga.edu/about/personnel-directory/browse/county.html) or Dr. Jonathan Oliver (UGA Blueberry Pathologist) at jonathanoliver@uga.edu.