Question: My cannas’ flowers don’t open properly, plus the leaves look like someone has fired a machine gun across them. They have holes in rows across the leaves.
Answer: That’s all damage of the canna leaf roller. It encases itself within the top growth of the plants. By the time the leaves start to unfurl, the flowers have often been ruined and the leaves are peppered with the damage. Use a systemic insecticide to prevent and control them. You may do so as a soil drench, or include one or two drops of a liquid detergent to help any spray adhere to the waxy leaves, and use a fine mist spray rather than one with large droplets.