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 the

The mycorrhizae might be killed by the fungicide.

Explanation:

Mycorehizae are one the microorganisms that can be found in the roots of the plants. They are in an association known as symbiotic relationship with the plants. This relationship is mutual because, both the microorganism and the plant benefit from it.

The plant produce food inform of carbohydrate for the growth of the fungus, while the fungus increase the surface area of the roots of the plant, thereby, enhancing water and nutrients intake.

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."