How large is the damage? If the damage is in large sections, then it might be an animal (although the leaves are toxic). If the holes are ragged and fairly big, check for a trail of slime—as slugs sometimes like to eat rhubarb leaves. Tiny to moderate holes in the leaves could be beetles, such as the Japanese beetle. Caterpillars, such as the European corn borer and imported cabbageworm, may sometimes attack leaves or stalks. Other pests, such as aphids or rhubarb curculio, make punctures rather than chewing holes. Look underneath the leaves, and at the base of plants in the soil, for any lurking pest. For slug control, see: http://www.almanac.com/pest/slugs Good luck!
How large is the damage? If the damage is in large sections, then it might be an animal (although the leaves are toxic). If the holes are ragged and fairly big, check for a trail of slime—as slugs sometimes like to eat rhubarb leaves. Tiny to moderate holes in the leaves could be beetles, such as the Japanese beetle. Caterpillars, such as the European corn borer and imported cabbageworm, may sometimes attack leaves or stalks. Other pests, such as aphids or rhubarb curculio, make punctures rather than chewing holes. Look underneath the leaves, and at the base of plants in the soil, for any lurking pest. For slug control, see: http://www.almanac.com/pest/slugs Good luck!