Many home gardeners find insects eating their irises. While irises are generally healthy, they are susceptible to heavy damage by the iris borer and thrips. Both of these pests threaten the health of irises, as well as their appearance. Properly identifying the insect causing the damage to your flowers is key to eliminating them or keeping them under control.
Thrips are common iris pests. These insects measure 1 to 3 mm in length. Long hairs cover their wings, and they inflict damage on irises with their rasping mouthparts. Flower thrips are the species that damage irises, along with daylilies, chrysanthemums, peonies, strawberries and roses.
The most destructive pest of irises, though, is the iris borer. The larvae of the iris borer is responsible for the damage to the plant. Iris borer larvae are pink worms that have brown heads and measure 1 to 2 inches in length.
Thrips use their rasping mouthparts to feed on the iris, causing silvery or white trails to appear on the leaves, flowers and stems of the plant. Irises infested with thrips may also experience dieback.
The iris borer larvae feed on the leaves of irises, causing ragged leaf edges, a water-soaked appearance, and dark streaks in the flowers, leaves and new buds. As the larvae continue feeding, they often move down to feed on the rhizome. As a result, soft rot sets in, causing yellow leaves and a foul odor.
Natural predatory insects often feed on thrips, keeping them under control. Lady beetles and parasitic wasps are two types of predatory insects that control thrip infestations. Deadheading irises is essential to preventing thrip infestations.
The iris borer is often controlled with several strategies. Remove all dead plant tissue and foliage and destroy before the spring; this kills any overwintering eggs. Inspect your flower bed for signs of iris borer infestation. Remove damaged irises and replace them. Continue to monitor your flower bed throughout the growing season for signs of iris borer infestations, such as chewed leaves.
Your local garden center has several chemical insecticides for thrip control. If possible, choose a product that is organic and does not harm other plants or predatory insects.
Severe infestations of the iris borer may require chemical control methods to prevent major damage in your flower bed. Spray iris leaves when they reach 3 to 4 inches in length and repeat at two-week intervals. Choose a product with active ingredients such as neem, azadirachtin or endosulfan for best results.
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