Synergistic Effect of a Mixture of Benzimidazole and Iminoctadine Triacetate for the Preharvest Control of Benzimidazole-Resistant Penicillium digitatum, a Causal Agent of Citrus Green Mold in Japan

Green mold, caused by Penicillium digitatum, is the leading cause of citrus decay in Japan. Due to a ban on the post-harvest fungicide application in Japan, the preharvest application of benzimidazoles has been used and demonstrated good efficacy since 1971. A benzimidazole resistant P. digitatum strain was first isolated from a packinghouse in 1974, and more cases were reported in subsequent years. On the other hand, very few cases were reported from the grove for two decades. However, by the mid-1990s, when the field incidences of benzimidazole resistant strain started to increase, the effect of benzuimidazoles became unstaible. An alternative to a benzimidazoles, iminoctadine triacetate, exhibited good antifungal activity against P. digitatum in vitro, but its efficacy was inconsistent in the field. We examined the efficacy of a mixed application of iminoctadine triacetate and benzimidazoles against each fungicide by itself based on five years of data from multiple locations. The results indicated a synergistic suppression on green mold, where the efficacy of the mixture was consistently greater than treatments with either fungicide alone. The improved efficacy was considered acceptable for a practical use by the industry, and lead to a development of a pre-mixed commercial product, Beftopsin flowable in 2006

Emergence of Benzimidazole- and Strobilurin-Quinone Outside Inhibitor-Resistant Strains of <em>Colletotrichum gloeosporioides</em> sensu lato, the Causal Fungus of Japanese Pear Anthracnose, and Alternative Fungicides to Resistant Strains

Japanese pear anthracnose (JPA) can cause severe tree defoliation during the growing season. Infected trees become weak and produce fewer flower buds the following spring. This economically serious fungal plant disease has affected cultivated pears in Japan since 1910. Initially, JPA was controlled by benzimidazole fungicides. However, benzimidazole-resistant pathogen strains emerged in the late 1990s, and the range of JPA has expanded in Japan. Since then strobilurin-quinone outside inhibitors (ST-QoIs) such as azoxystrobin and kresoxim-methyl became popular, but ST-QoI-resistant pathogen strains appeared. By 2005, JPA control became difficult once again. In this chapter, we outline the history of JPA fungicide resistance problems, assess advantages and disadvantages of available fungicide options, and develop JPA management strategies based on evidences we obtained from a series of field and lab studies