When pathogenic fungi are found growing on the roots of grapevines, grape farmers sometimes respond by covering the ground around their vines with plastic sheeting and pumping a gaseous fungicide into the soil. The most important concern of grape farmers who engage in this practice should be that the

A) sheeting is transparent so that photosynthesis can continue.
B) lichens growing on the vines' branches are not harmed.
C) the plastic sheeting decreases evaporation of water from the soil.
D) fungicide might also kill mycorrhizae.
E) fungicide might also kill the native yeasts residing on the surfaces of the grapes.