CAUTION: This information was developed for North Carolina and may not apply to other areas.
Adult azalea leafminers are small, yellow moths with purplish markings on the wings. The wingspan is about 1/2 inch.
The leaf-mining stage is a yellowish caterpillar about 1/2 inch long. It has three pairs of prolegs found on the abdominal segments three, four and five. The proleg hooks (crochets) are singly arranged in a U-shaped pattern with a series of crochets within the U.
The azalea leafminer is found in most states where azaleas are grown, and azaleas are the only known host for this insect. The leafminer larva has less effect on plants grown outdoors in NC, but it may do considerable damage to cuttings in the greenhouse or sometimes outdoors in more southern states such as Georgia and Florida. Mining within the leaf, the young larva causes the formation of brown blisters on the leaf surfaces. As the larva matures, it emerges from within the leaf tissue and rolls the edge of a leaf around itself for protection, while feeding on the leaf surface. Seriously injured leaves usually turn yellow and drop, thereby causing an unsightly plant.
Eggs are deposited singly on the undersides of leaves along the midribs, usually one to five per leaf. The young (larvae) hatch in about 4 days, mine into the leaves, and feed inside them. At this stage, the leaves appear to have blisters. If a leaf is held up to the light, the larvae can be seen inside. When about one-third grown, the larva emerges, moves to the tip of a new leaf and rolls it up for the protection while feeding and growing. When nearly grown, the larva rolls up the margin of the leaf and spins a cocoon inside. The moth emerges from the cocoon, mates and deposits eggs for another generation. Under greenhouse conditions, the larvae may be found at any time during the year. The insect overwinters outdoors as a larva or pupa. Adults appear and females lay eggs about the time plants bloom in the spring.
Because the larva protects itself by mining into or rolling the leaf, this insect is not easy to control. Hand picking or pruning is very effective where practical. Several insecticides such as Conserve, Avid, Azadirachtin, or a pyrethroid should give satisfactory control when applied at the first sign (probably April-May) either of the adult moth or of foliar injury by the larvae. One or two applications, 1 to 2 weeks apart, are usually sufficient. Consult the North Carolina Agricultural Chemicals Manual for recommendations. Homeowner lawn and garden insecticides containing cyfluthrin or permethrin should be available. Neem oil containing products may also be helpful. Be sure to read and follow all label instructions, including intervals between spraying and harvest.
The University of Georgia has identified some azalea varieties resistant to azalea leafminer.
Published by North Carolina Cooperative Extension ServiceDistributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.