When pathogenic fungi are found growing on the roots of grape vines, 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 thelichens growing on the vines' branches are not harmed. fungicide might also kill the native yeasts residing on the surfaces of the grapes. sheeting is transparent so that photosynthesis can continue. fungicide might also kill mycorrhizae.