Mary Helen Ferguson, Louisiana State University Agricultural Center
Fungicide resistance poses a challenge to growers of many crops. It is vital to know if fungicides are likely to be effective so that diseases are managed and money is not wasted. Populations of Botrytis cinerea, which causes grey mold in strawberries, have developed resistance to a number of fungicides formerly effective against it. Furthermore, resistance to the quinone outside inhibitor (QoI, FRAC 11) group of fungicides has been identified in the pathogen that causes anthracnose fruit rot of strawberries (Colletotrichum acutatum species complex; Figure 1). Forcelini and Peres (2018) found that 49 percent of 137 isolates collected from fields in the southeastern U.S. during the 2015-2016 season were resistant to azoxystrobin.
Another challenge to southeastern U.S. strawberry growers in recent years has been Pestalotia leaf spot and fruit rot (Figures 2a and 2b). A Neopestalotiopsis sp. genetically distinct from Neopestalotiopsis rosae has been identified by Baggio et al. (2021) as the cause of severe disease on strawberries. Because of the difference in the severity of disease associated with the newly identified Neopestalotiopsis sp. and other Neopestalotiopsis species, Kaur et al. (2023) have developed a molecular technique for detecting the aggressive genotype.
This article provides information about labs in the southeastern U.S. that offer tests for fungicide resistance in the strawberry grey mold (Botrytis cinerea) and anthracnose (Colletotrichum spp.) pathogens. It also identifies labs that detect aggressive Neopestalotiopsis using the Kaur et al. (2023) protocol.
Molecular Plant Pathogen Detection Lab
Clemson’s Molecular Plant Pathogen Detection (MPPD) Lab (Phone 864-646-2133) offers tests for fungicide resistance in Botrytis and Colletotrichum. They test Botrytis isolates for resistance to the following active ingredients: thiophanate methyl (FRAC 1); iprodione (FRAC 2); boscalid, fluopyram, isofetamid, and penthiopyrad (FRAC 7); cyprodinil (FRAC 9); pyraclostrobin (FRAC 11); fludioxonil (FRAC 12); and fenhexamid (FRAC 17). In Colletotrichum, they test for resistance to pyraclostrobin, as a representative of the QoI fungicides. In-state (South Carolina) and out-of-state samples cost $80 and $100, respectively. For Botrytis samples, up to ten isolates are each tested for resistance to each active ingredient. Clemson’s MPPD Lab also tests for aggressive Neopestalotiopsis. Contact the lab for pricing information.
Plant Molecular Diagnostics Lab
The University of Georgia (UGA) Plant Molecular Diagnostics Lab (MDL) (Phone 229-386-3372) offers resistance testing in both Botrytis and Colletotrichum for the following active ingredients: difenoconazole and prothioconazole (FRAC 3); benzovindiflupyr, fluopyram, penthiopyrad, and pydiflumetofen (FRAC 7); and azoxystrobin and pyraclostrobin (FRAC 11). They test five isolates per sample. The cost for both in- and out-of-state samples is $200.
UGA’s MDL also tests for aggressive Neopestalotiopsis. They charge $60 for in- and out-of-state samples. If the lab determines that DNA sequencing needs to be done to confirm the identification, there is an additional $20 charge.
Gulf Coast REC Plant Clinic
The University of Florida Gulf Coast Research and Education Center’s Plant Clinic (Phone 813-419-6599) tests strawberry samples for aggressive Neopestalotiopsis. They charge $40 for in- and out-of-state samples.
Baggio, J.S., Forcelini, B.B., Wang, N.Y., Ruschel, R.G., Mertely, J.C., and Peres, N.A. 2021. Outbreak of leaf spot and fruit rot in Florida strawberry caused by Neopestalotiopsis spp. Plant Disease. 105:305-315.
Forcelini, B.B, and Peres, N.A. 2018. Widespread resistance of QoI fungicides of Colletotrichum acutatum from strawberry nurseries and production fields. Plant Health Progress. 19:338-341.
Kaur, H., Gelain, J., Marin, M.V., Peres, N.A., and Schnabel, G. 2023. Development of a molecular tool for identification of a new Neopestalotiopsis sp. associated with disease outbreaks on strawberry. Plant Disease. 107:5, 1544-1549.