ARS | Publication request: A microtiter assay shows effectivness of fungicides for control of Colletotrichum spp from strawberry

Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2011
Publication Date: October 3, 2012
Citation: Smith, B.J., Wedge, D.E., Pace, P.F. 2012. A microtiter assay shows effectivness of fungicides for control of Colletotrichum spp from strawberry. International Journal of Fruit Science. 13:1-2, 205-216.

Interpretive Summary: Fruit rot diseases of strawberry represent serious problems for producers in many areas of the world, and they are particularly severe in the southeastern U. S. where disease is often favored by warm temperatures and frequent rains during the harvest season. Anthracnose diseases caused by Colletotrichum spp. can be especially devastating since they may cause fruit rot and plant death. Sixteen agrochemicals that are currently used or have been used for control of strawberry pests and diseases were tested in a microtiter assay for in vitro activity against isolates of C. acutatum, C. fragariae and C. gloeosporioides collected from strawberry. Older, protective, multi-site fungicides (chlorothalonil, captan, thiram, and dodine) inhibited the growth of isolates of all three Colletotrichum species at the highest concentration tested. The C. acutatum isolates were insensitive to benomyl, thiobendazole, vinclozolin, and iprodione. Two of the newer fungicides in the study (azoxystrobin and cyprodinil) inhibited the growth of most isolates at the lowest concentration. Two commercial formulations of these newer fungicides are now labeled for disease control on strawberries. This information will be used by research scientists, extension agents and growers making disease control decsions.

Technical Abstract: The anthracnose pathogens, Colletotrichum acutatum, C. gloeosporioides and C. fragariae, have developed resistance to some fungicides. We used a micro-dilution broth assay to test in vitro the activity of 16 chemicals against ten isolates of Colletotrichum spp. using a dose-response format. At a concentration of 30 µM captan, thiram, cyprodinil, chlorothalonil, azoxystrobin, and kelthane provided nearly 100% inhibition of the growth of all ten Colletotrichum isolates. Iprodione, vinclozolin, metalaxyl, and fosetyl-Al did not inhibit growth of any isolate. Benomyl and thiobendazole inhibited growth of the C. fragariae and C. gloeosporioides isolates, but did not inhibited growth of the six C. acutatum isolates.