Determination of efficacy of certain fungicides against cryphonectria parasitica (murrill) barr (chestnut blight)

Chestnut blight, caused by Cryphonectria parasitica, is a significant disease that leads to the death of numerous trees in chestnut-growing areas worldwide. The disease damages the bark tissue on the trunk, branches, and shoots of the trees, preventing water and nutrient uptake, which causes the trees to partially or completely die back. Due to the limited control methods available today, the disease cannot be managed to the desired level. In the past, the effects of fungicides against chestnut blight were investigated, and some were found to be effective in vitro. However, the low efficacy of fungicides on trees, even systemic ones, due to difficulties in translocation within the bark tissue has prevented the practical application of chemical control. For this reason, chemical control, a much more accessible and applicable option for growers, is not included in the technical instructions for managing the disease. This study aims to fill this gap by testing the efficacy of some new-generation systemic fungicides against the causal agent of chestnut blight. In the study, the efficacy of fungicides with the active ingredients flutriafol, myclobutanil, cyprodinil, prochloraz, and tebuconazole on the mycelial growth of Cryphonectria parasitica was investigated. In the in vitro trials conducted on potato dextrose agar (PDA) medium, eight different rates of the fungicides, ranging from 0,1 to 300 ppm, were tested. At the end of the seventh day of incubation period, all fungicides significantly inhibited mycelial growth, although their ranks of effectiveness varied. Tebuconazole, which showed the highest efficacy, inhibited growth by 100% at the rates above 0,1 ppm, while the same effect obtained from the rates above 0,3 ppm for prochloraz, 1 ppm for myclobutanil, 10 ppm for flutriafol, and 30 ppm for cyprodinil. To test the in vivo equivalent of this high potential observed in the laboratory, efficacy trials were conducted on 'Golden Delicious' apple fruits and healthy chestnut cut twigs. The fungicides were applied into wells made in the tissues, which were then infected with the fungus. While only the flutriafol application resulted in a statistically significant reduction in lesion size in the apple fruit tests, none of the fungicides were able to significantly reduced the development of canker lesions in the more critical chestnut cut twigs trials. This situation reveals that these chemicals, which are highly effective in the laboratory, do not demonstrate the same success when applied to plant tissue. Therefore, it is understood that the primary obstacle to chemical control is the inability to effectively deliver the active ingredients to the target tissues within the plant. For this reason, it is of critical importance that future studies focus on developing new application and injection methods to transfer these fungicides into plant tissues, in order to translate their efficacy into practice.