Brussels sprouts have a lot of the same pests that cabbage does. If the holes are tiny, but lots of them, these might be from flea beetles; see http://www.almanac.com/content/flea-beetles for more about control. If the holes are large and ragged, they might be from cabbage loopers or imported cabbageworms.
For cabbageworm control, please see: http://www.almanac.com/content/cabbageworms
For cabbage looper control, options include handpicking or using BTK or garlic oil.
Brussels sprouts have a lot of the same pests that cabbage does. If the holes are tiny, but lots of them, these might be from flea beetles; see http://www.almanac.com/content/flea-beetles for more about control. If the holes are large and ragged, they might be from cabbage loopers or imported cabbageworms.
For cabbageworm control, please see: http://www.almanac.com/content/cabbageworms
For cabbage looper control, options include handpicking or using BTK or garlic oil.