Barriers Mechanical barriers are most effective when aimed at excluding one or a few pests rather than all pest. Aluminum foil and other reflective mulch has been shown to repel aphids. However, the environmental impact and energy consumption involved in making aluminum foil deserves consideration. Crushed eggshells or hydrated lime spread around plants will discourage slugs. While heavy mulch is good for weed control, it gives slugs a place to hide.
Collars made of cardboard, tin cans, or aluminum foil are effective barriers to cutworms.
When placed around seedlings and inserted about halfway into the soil, collars prevent cutworms from moving to seedlings stems. Use of screening around potato storage areas can prevent the entry of tuberworm moths. Mounding soil around grape vines can prevent the emergence of grape root borer moths. Net-covered cages over young seedlings will help prevent insect, bird, and rabbit damage. Cheesecloth screens for cold frames and hot beds will prevent insect egg laying.