Holes in Leaves of Rhubarb
Rhubarb is a long-lived low maintenance vegetable with very few pests. So when holes appear in the leaves it may cause you to worry.
Several leaf spot diseases can cause small red or brown spots on the leaves and stems. The spotted tissue dies and often drops out, leaving holes in the leaves. Remove diseased leaves and stems as soon as they're discovered and do a thorough clean up in fall.
The rhubarb curculio is an occasional pest of rhubarb, feeding on the leaves and stems. You may notice sap oozing from the damaged stems or notches of missing tissue on the leaf edges. This pest is ½ inch long, has a large snout and its back is covered with a yellowish powder. Remove these pests when found and drop them in a can of soapy water.
Keep the garden weed-free and avoid overhead watering to keep plants healthy.
A bit more information: Some weeds are hosts for these diseases and insects that attack rhubarb. Managing weeds can reduce the risk of pest problems. Fortunately, established plants survive and recover with proper garden cleanup and care.