Fruit Quality, Phytochemical Content, and Disease Severity of Muscadine Grapes Affected by Fungicide Applications

Muscadine grapes are high in phytochemicals beneficial to humans, such as resveratrol and ellagic acid. Four studies were conducted to explore the relationship between phytochemical content, berry quality, and disease control following full season or early season applications of fungicides. In each study foliar and fruit diseases were lower in the full season treatment compared to the control, and some treatments with fewer applications reduced fruit diseases to the same level as the full season treatment. In Study 1 the full season (9 applications) and azoxystrobin treatments (3 applications) resulted in significantly lower berry disease scores than the control treatment. There were no significant differences in vine vigor, foliar diseases, or bitter rot scores among treatments where fungicide applications were stopped at various preharvest intervals ranging from 56 to 0 days (Study 3), or in disease scores between the full season (8 applications) and early season treatments (4 applications) of six fungicide treatments (Study 4). Sugar levels were highest in berries from the full season, azoxystrobin, and control fungicide treatments, and berries from the least efficacious treatments for disease control had almost ten times as much resveratrol as those from the most efficacious treatments (Study 1). Ellagic acid and resveratrol levels were lower in berries from fungicide treated vines than from untreated vines (Study 3). The number of fungicide applications can be reduced to as few as four without an increase in berry disease scores; however, when diseases of muscadine grapes are controlled, levels of beneficial phytochemicals may decrease.