Final answer:
The disadvantage of conservation tillage methods is the increased risk of pest infestation due to crop residues left on fields, which can harbor pests.
Step-by-step explanation:
One disadvantage of conservation tillage methods is D. Increased risk of pest infestation. While conservation tillage, including minimal or no tillage methods, provides numerous environmental benefits such as reducing erosion and improving water infiltration, it can lead to increased pest populations. This is because the crop residues left on the field can provide shelter and breeding grounds for pests, resulting in a potential need for more rigorous pest management strategies.