Isolates of Sclerotium rolfsii exhibiting varying degrees of in vitro fungicide sensitivity were exposed to fungicides in field microplots in 1995 and 1996. Individual peanut (Arachis hypogaea L.) plants in 0.9-m microplots were inoculated with isolates of S. rolfsii collected from peanut fields throughout Georgia. The 60 isolates used in the study represented the full range of sensitivity to the fungicides tebuconazole, flutolanil, and PCNB. After inoculation, microplots were treated with recommended rates of tebuconazole (0.227 kg ai/ha), flutolanil (0.337 kg ai/ha), PCNB (5.6 kg ai/ha), or were left untreated. Disease ratings were made at harvest, and pod yield from each plant was recorded. In both years, disease severity was significantly lower in treated microplots for all three fungicides. Isolates with lower in vitro fungicide sensitivity responded as well to labeled rates of all three fungicides as those with high in vitro sensitivity. In vitro sensitivity and percent control in treated microplots were not correlated for all three fungicides. Fungicide sensitivity and the level of infection in nontreated microplots also were not correlated for flutolanil and tebuconazole indicating that virulence was not affected by fungicide sensitivity. However, there was a negative correlation between in vitro sensitivity to PCNB and the level of infection in nontreated microplots in 1995, indicating that isolates with lower in vitro sensitivity were more virulent. However, this trend was not observed when the same isolates were evaluated in 1996. In 1995, plants in PCNB-treated microplots had a significantly higher yield than those in the nontreated microplots. In 1996, all fungicide treatments significantly enhanced yield. Because in vitro sensitivity and field efficacy were not correlated for all three fungicides, labeled rates should control stem rot in the field.
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Keywords: Groundnut, sensitivity correlation, Sclerotium rolfsii, virulence
How to Cite:
Franke, M. & Brenneman, T. & Stevenson, K., (1998) “Stem Rot of Peanut: Relationship Between in Vitro Fungicide Sensitivity and Field Efficacy of Fungicides”, Peanut Science 25(2), p.76-80. doi: https://doi.org/10.3146/i0095-3679-25-2-4