I'm a big fan of the Copper John and Copper Bob series of flies, but prefer a slight tweak for early season fishing. The Corn Bob is a staple in my boxes year-round, but really comes into its own from June through July.
The reason? That's when stoneflies hold forth, and the Corn Bob does a good job of imitating the aquatic forms of those insects. The yellow goose biot tails
and optional legs are key, giving the standard pattern a golden flash that helps trigger strikes. In smaller sizes, say, a #14, it imitates a Yellow or Lime Sally nymph; in sizes 8-12 I use it for golden stones, and typically include the legs.
It doesn't stop there, either. By late June and early July we're seeing the first PMDs on the Columbia and Bow Rivers, and the Corn Bob works for those as well when tied down to #14 and smaller.
A few tying tips are in order ... I use darker, tungsten beads for all my nymphs and wet flies. Gone are the days when heavily fished trout chomp on traditionally colored beads like gold and silver; I've watched Elk River cutties repeatedly refuse a bright beadhead only to chase the first black one that came along. Stick to black, nickel, or olive beads and you'll hook more trout wherever you fish.
As for the tungsten - yes, it's a bit more expensive, but it's also the fastest-sinking material out there and environmentally friendly. I rarely guide with anything but dries, hopper-droppers, and short-leash nymphs, so I need the latter to get down in a hurry. That's especially the case on the swift freestone streams and rivers out West. Tungsten does the trick.
My flies aren't pretty. I'm the first to admit that. But they are practical, tied with quality materials and made to last. I appreciate a beautifully tied pattern as much as anyone (jealousy alert), but the fish won't care if you finish the thorax with epoxy or perfectly trim the loose ends. Bottom line: tie the fly you're proud to fish or tie to someone else's tippet; don't be swayed by 'flawless,' mass-produced flies that fall apart in the first 10 minutes.
Besides, when's the last time you finished the day with the same fly you started with? Masterpieces are tough to appreciate when they're stuck in underwater stumps or dangling from overhead branches.
To tie the Corn Bob follow the same general steps as with the Copper Bob or John. This video is an excellent guide.