Azalea Leafminers Found
Azalea leafminers can be found in most states where azaleas are grown but are especially damaging in greenhouses where cuttings are rooted. Danny Lauderdale has recently found this pest in eastern North Carolina. Lauderdale is the new Area Specialized Agent working in eastern NC with Nurseries and Greenhouses.
Azalea leafminers overwinter as pupae in rolled leaves or as larvae in mined leaves. Adult moths are no more than one-half inch long and yellow with purple markings near the base and apex of their forewings. They stand at attention when at rest at a 60 degree angle to the leaf and have antennae the length of their body. In our area, adult azalea leafminer moths emerge about the same time that the plants produce flowers in the spring. After mating, adults deposit individual eggs (up to 5) along the mid-vein on the underside of leaves. The eggs can be seen with a hand lens as can the larvae that hatch in about 4 days. The tiny yellow caterpillars mine into the leaves to feed inside leaving blisters in the leaves.
The larva emerges when it is about one third grown and moves to the tip of a new leaf where it rolls it up for protection. Leaf tiers is the term used for the larva that attack terminal buds of plants, binding leaves with strands of silk to create shelter for themselves while they feed. The leaf tissue in the abandoned mines dies and turns brown. Larvae reach one-quarter to one-half inch in length at maturity and spin a cocoon inside the protection of the leaf tip. The adult moth emerges from the cocoon in about 7 days, mates and deposits eggs for another generation. There are multiple generations each year in the south. Under greenhouse conditions larvae may be found at any time of the year.
Control is not easy since the larvae are protected by the azalea leaf. Hand picking or pruning is very effective where possible. Several insecticides are available for control when applied at the first sign of the pest in the spring. Adults may be targeted with contact insecticides like pyrethroids (bifenthrin, cyfluthrin, permethrin). Abamectin (translaminar systemic), azadirachtin (insect growth regulator, botanical, and antifeedant), and will aid in control of larvae at the first sign of injury. Systemic products to consider for rotation are acephate (organophosphate) and acetamiprid (neonicotinoid with some activity on caterpillars). Scout weekly starting at flowering to determine the need for treatment. There are some parasitoids that target this pest.
At present in eastern NC this pest is in its 2nd generation as an adult and will be laying eggs, hatching, and leaf mining soon. Inspect azaleas now for adults, signs of leafminers and leaf tiers, and symptoms of damage. More detailed information can be found in: https://www.ces.ncsu.edu/depts/ent/notes/O&T/shrubs/ort003e/ort003e.htm.