Irises are popular garden fixtures, known for their striking blooms and sword-like foliage. Although the plant contains compounds that make the leaves and rhizomes somewhat toxic, this natural defense does not deter all garden pests. Animals and insects often damage or destroy healthy plants, treating the iris as a readily available food source. Protecting these perennials begins with understanding the specific culprits behind the damage.
Animals That Consume Iris Foliage and Flowers
Damage to the upper parts of the iris, including leaves, buds, and flowers, is the most visible sign of a problem, typically caused by larger mammals and small surface-dwelling pests. Deer and rabbits are frequent offenders, and the type of chewing helps distinguish between the two. Deer lack upper incisors, so they tend to tear and rip the foliage, leaving a ragged, shredded appearance on the leaves and flower stalks. Rabbits possess sharp front incisors that allow them to make a clean, forty-five-degree cut, often shearing off new growth or entire flower buds close to the ground.
Small mollusks like slugs and snails target the foliage, especially tender new shoots emerging in spring. Their feeding leaves characteristic irregular holes in the leaves and flowers, creating a ragged appearance. The most definitive sign of these nocturnal pests is the silvery, dried slime trail left across the leaves and surrounding soil. Climbing cutworms also chew large notches out of the sides of iris leaves, often feeding at night and hiding in mulch or debris during the day.
Pests That Attack Iris Rhizomes and Roots
Subterranean pests pose a more fatal threat because their damage is hidden underground until the plant begins to visibly decline. Voles and gophers are the primary mammalian culprits, tunneling beneath the soil surface to feed on the fleshy, nutrient-rich rhizomes, which are the plant’s food storage organs. A plant that suddenly wilts and falls over without foliage damage often indicates the entire rhizome has been cleanly eaten away at the base, leaving no root structure. The presence of small tunnels or pushed-up mounds of dirt near the iris fans confirms these rodents are responsible.
The iris borer, the larvae of the moth Macronoctua onusta, is the most destructive insect pest for irises. The pinkish-white larvae hatch in early spring and bore into the leaves, leaving translucent streaks as they tunnel downward. Once the borer reaches the rhizome, it tunnels through the tissue, hollowing it out and causing the plant to collapse. This feeding creates an entry point for bacterial soft rot, which turns the rhizome into a soft, foul-smelling mush, differentiating borer damage from clean mammal chewing.
Effective Strategies for Protecting Iris Plants
Protecting iris foliage from large browsers involves using physical and chemical deterrents tailored to the specific animal. For rabbits, a simple two-foot-tall chicken wire fence is an effective physical barrier, while deer require a much taller, eight-foot fence or netting draped directly over individual plants. Repellents offer another layer of defense, with taste-based formulas (like rotten eggs) or scent-based products (like predator urine) needing frequent reapplication, especially after rain.
For subterranean mammals like voles and gophers, the most reliable long-term solution is to plant the rhizomes inside protective wire cages or mesh baskets made of hardware cloth. This barrier prevents the rodents from accessing the rhizome while still allowing the roots to grow out into the surrounding soil. Managing the iris borer requires a cultural control strategy focused on interrupting its life cycle. Gardeners should conduct a thorough fall cleanup, removing and destroying old iris foliage and debris where the borer moth lays its overwintering eggs. In the spring, inspecting new leaves for streaking and crushing the young larvae can stop the insect before it tunnels down to the rhizome.