Answer: The columbine leaves have what are called leaf miner insects. They tunnel throughout the leaves and then exit. Leaf miners are the larvae of a flies, moths or beetles. The adult lays eggs by piercing the leaf surface. When the egg hatches the larva tunnels through the leaf, feeding and growing. When it is mature enough it makes a little exit hole and spins a web that helps it float down to the soil surface. There it pupates and then becomes an adult. There's really no effective pesticide for the larvae because it is protected inside the surface of the leaf; there's no effective way to stop the adult from laying eggs. If you timed it right, you might be able to kill the larvae when it pupates in the soil but most gardeners don't bother. Aside from making little tunnels in the leaves, they don't really hurt your plants.
As for the cannas - I'd plant them in pots to ensure good drainage, even when the spring is wet. You might also consider raising the planting bed a few inches to help it drain faster.
Best wishes with your garden!
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