S. J. MacKenzie,
J. C. Mertely, and
N. A. Peres, University of Florida, Department of Plant Pathology, Gulf Coast Research and Education Center, Wimauma, FL 33598
The ability of fungicides to control Colletotrichum crown rot of strawberry caused by C. gloeosporioides was examined over three seasons. A single application of each fungicide was made 2 days before inoculation (2 DBI) or 1 day after inoculation (1 DAI) with conidial suspensions of C. gloeosporioides. The proportion of plants collapsed on one date at the end of each season was evaluated. In a combined analysis, there was a significant fungicide treatment-season interaction (P = 0.004). Percent mortality was 64% over 3 years in control plots that were inoculated with C. gloeosporioides but not treated with fungicide. Captan applied 2 DBI consistently reduced plant mortality (mean mortality = 17%). However, it was not as effective when applied 1 DAI (mean mortality = 46%). Azoxystrobin, pyraclostrobin, and thiophanate-methyl all reduced plant mortality relative to the control if applied 2 DBI (mean mortality = 46% for azoxystrobin, 37% for pyraclostrobin, and 41% for thiophanate-methyl) or 1 DAI (mean mortality = 29% for azoxystrobin, 27% for pyraclostrobin, and 32% for thiophanate-methyl). Results indicated that these fungicides were more effective when applied 1 DAI; however, lower plant mortality was not always observed with postinoculation applications. Cyprodinil + fludioxonil reduced mortality relative to the control, but there was no consistent evidence that it was more effective when applied at 2 DBI (mean mortality = 39%) than when applied 1 DAI (mean mortality = 40%). Similarly, mortality in plots treated with thiram 2 DBI (mean mortality = 30%) or 1 DAI (mean mortality = 32%) was not different. Potassium phosphite did not affect mortality, regardless of the timing of application (2 DBI mean mortality = 61%, 1 DAI mean mortality = 67%). The results indicated that an effective strategy for controlling Colletotrichum crown rot caused by C. gloeosporioides should be based on weekly applications of captan throughout the growing season. Azoxystrobin, pyraclostrobin, or thiophanate-methyl applications should be applied when weather conditions are highly favorable for disease development and the activity of contact fungicides such as captan or thiram might be compromised.