Laboratory and field efficacy of certain fungicides against gummosis of citrus disease in Tunisia

Gummosis, caused by Oomycota, is a devastating disease for citrus production in Tunisia. Due to the limited strategies available for this disease management, the laboratory and field applications of some commercially fungicides were conducted.Using the mycelia growrh ratios, from the tested fungicides, metalaxyl, cymoxanil, propamocarb, and mancozeb are the most efficient fungicides ,with 94.75%, 94.62%, 91.13%, and 90.75% in reducing the mycelial growth of Oomycota pathogens, respectively. While azoxystrobin and fosetyl-Al have generated a moderate growth reduction, with 81.25% and 74.25%, respectively. The lowest fungicides effect was obtained with trifloxystrobin, thiophanate-methyl and chlorothalonil, with 38.87%, 36.25%, and 15.25%. In field experiments, metalaxyl and fosetyl-Al were applied as paint trunk and as foliar spray, against infection by Phytophthora nicotianae. The results showed that the metalaxyl was more efficiency in reducing the length lesion caused by P. nicotianae, than the fosetyl-Al. Furthermore, paint treatments revealed to be more effective in reducing lesion expansion than foliar spray treatments both in curative and in residual activity. Moreover, citrus clementine variety is the most susceptible to P. nicotianae infection, while the most tolerant is tangerine variety.Â