Discovering holes in rose leaves signals that something has been feeding on the foliage. While the damage is often unsightly, it rarely threatens the plant’s long-term survival or ability to bloom. Understanding the specific pattern of damage is the fastest way to identify the culprit, which is usually an insect or an environmental issue. Correct identification allows you to choose the most appropriate response to protect your roses.
Primary Causes: Insects That Chew Irregular Holes
Ragged, irregular holes in rose leaves are most commonly caused by specific insect pests active during the growing season. Rose slugs, which are sawfly larvae, typically cause the first damage in spring and early summer. They feed on the soft tissue, often starting on the underside. Smaller larvae scrape away the surface, creating a “window-pane” effect where the tissue eventually falls out to form a hole. Larger sawfly larvae chew entirely through the leaf, leaving small, irregular holes or notches.
Later in the season, starting in mid-summer, the damage shifts to the adult Japanese beetle (Popillia japonica). These beetles are known for their skeletonizing feeding pattern, consuming the soft leaf material between the major veins. They leave behind only a lace-like network of tougher vascular tissue. This feeding can occur rapidly, compromising the leaf’s ability to photosynthesize, especially when multiple beetles congregate. Other common caterpillars also create ragged holes by chewing through the foliage, but their presence is usually less consistent than seasonal beetle outbreaks.
The Distinctive Sign of Leaf Cutter Bees
The beneficial leaf cutter bee (Megachile species) causes a distinct type of leaf damage. These insects do not eat the leaf material. Instead, they cut out smooth, semi-circular or nearly round discs from the edges of the rose leaves. The bee uses its mandibles to harvest these precise pieces, which are then rolled up and used to construct protective cells for their eggs inside their nests.
The damage is purely cosmetic and does not harm the overall health of the rose bush. Leaf cutter bees are important native pollinators. Since the holes are a byproduct of their reproductive cycle, the damage is temporary and stops once nesting is complete. The clean, surgical cut distinguishes this activity from the ragged chewing caused by pest insects.
Non-Insect Causes and Environmental Damage
Not all holes in rose leaves result from insect feeding; some damage is caused by environmental factors or disease. Physical damage from strong wind, hail, or accidental tearing results in irregular holes or split leaves. This damage is typically random, affecting only a few exposed leaves, and lacks the consistent patterns seen with pest activity.
Another non-insect cause is a fungal issue known as shot hole disease. This disease begins as small, discolored spots on the leaf surface that eventually turn brown and dry out. The plant isolates the infected tissue, which then drops out of the leaf entirely, leaving a small, smooth-edged hole. Unlike pest damage, this is preceded by visible leaf spots and is often exacerbated by wet, humid weather.
Identifying the Culprit and Immediate Management
Confirming the identity of the pest often involves scouting and elimination. Sawfly larvae are tiny, caterpillar-like insects that hide on the underside of the leaves; careful inspection is necessary to spot them, especially in May and June. The presence of small, dark, pepper-like droppings, called frass, below the damage is a strong indicator of active chewing insects like sawflies or caterpillars.
For rose slugs and other soft-bodied larvae, a strong jet of water from a garden hose directed at the underside of the leaves knocks them off the plant. Japanese beetles are best managed by handpicking them in the early morning, when they are less active, and dropping them into soapy water. Because leaf cutter bees are beneficial pollinators and their damage is cosmetic, no control measure is necessary. If shot hole disease is suspected, management focuses on reducing moisture by pruning for better air circulation and avoiding overhead watering.