ORNAMENTALS AND TURF
From: Steve Frank, Extension Entomologist
Keep Alert for a New Crape Myrtle Pest
One of the newest pests to plague urban trees is the crape myrtle bark scale, Eriococcus lagerstroemia. It is not yet in North Carolina, but it is probably coming soon. The first detection of crape myrtle bark scale in the U.S. was just outside Dallas, Texas, in 2004. Since then, it has spread throughout much of Texas. It has also spread to Arkansas, Louisiana, Oklahoma and Tennessee. Last week it was also found in Georgia.
Crape myrtle bark scale is similar to azalea bark scale and oak eriococcid scale that is common on willow oaks in Raleigh. Female scales produce fluffy white filaments that cover their bodies. In spring, they produce eggs beneath their body then die. Tiny crawlers hatch from the eggs and spread around the plant. Scale crawlers can also be spread by the wind. The crawlers settle in their new spot and begin producing white filaments as they grow. They have at least 2 overlapping generations in Arkansas and probably more in warmer areas.
At low density, crape myrtle bark scale feeds in rough areas around branch collars, but as the population increases, all the bark may be covered. These scales are most often noticed because trees become covered in black sooty mold. At first, many people assume this is from crape myrtle aphids so the scales may go undetected. If you notice unusually heavy honeydew and sooty mold on crape myrtles, take a closer look at the bark.
Since this is such a new pest in the U.S., we do not have a good idea how to manage it. Drench applications of neonicotinoids have provided some control in Texas. However, since crape myrtles flower continually and attract a slew of pollinators, this may not be the best option. Insect growth regulators such as pyriproxyfen and buprofezin are effective for many other scales and may be a good option. Horticultural oil, especially the heavier dormant rate, can reduce scale abundance also.
White crape myrtle bark scales on a crape myrtle trunk blackened with sooty mold. Photo: S. D. Frank.
Lecanium Scale Crawlers!
Oak and European fruit lecanium scale are one of the largest soft scales in our area. Scale ovisacs are brown and rounded reaching 6 mm in diameter. This is the most noticeable stage and is present right now. As members of the soft scale family Coccidae, lecanium scales produce honeydew that can cause sooty mold on oaks or plants below. Oak lecanium scale primarily infests oaks trees. However, European fruit lecanium can infest many tree species including oaks. They are impossible to tell apart without a microscope and even then it is hard. Large populations can reduce growth and vitality especially in newly planted trees.
Eggs are present now under adult scale covers and crawlers are beginning to hatch. The crawler stage should be targeted for best efficacy. On trees small enough to treat foliage, horticultural oil can be used. On larger trees, a systemic such as dinotefuran can be applied as a drench or trunk injection. This scale is not easily eradicated and optimal control measures are still unclear. It is attacked by many parasitoids and predators that can reduce scale abundance if protected from insecticides. A short video (https://www.youtube.com/watch?v=tD6I7P6BdKU) by graduate student Emily Meineke describes the scale biology. She is conducting research (http://ecoipm.com/research/urban-ecology/) to understand why lecanium scale outbreaks on urban trees.
Lecanium scale ovisac on willow oak. Photo: S. D. Frank.
From: Adam G. Dale, Graduate Student and Steve Frank, Department of Entomology
Bagworms Active in Raleigh
Bagworms have been hatching for the last week or so. You can find the tiny caterpillars with tiny upright bags anywhere there are bags left from last year. The bagworm, Thyridopteryx ephemeraeformis, is a very common ornamental pest throughout the eastern United States. These pests overwinter as eggs within the mother’s bag. Larvae emerge from the bag during the months of May and June. Once they have emerged, they crawl or drift via a silk strand to nearby foliage where they begin to establish feed. Bagworms are relatively sedentary during their lifetime, most often remaining on the same tree until they pupate. Adult females are wingless and never leave the tree, while male bagworms pupate and develop into a small brown moth.
Bagworms feed on plant foliage and can cause a significant amount of damage in a relatively short period of time. Some common trees that they infest include: maple, sycamore, oak, poplar and apple while they mostly prefer conifers. The early instar caterpillars produce a silk bag on their posterior end that gradually collects plant tissue debris from them feeding. This creates a leafy bag that camouflages them as plant tissue. Since they don’t move much during their lifetime, they are commonly found in dense populations within the same tree. These dense populations have the potential to kill conifers within one to two seasons due to defoliation and are found more often on ornamental trees rather than in forests. Since they are so discrete and easily mistaken for plant tissue, pest management for these insects can be difficult and/or time consuming. One of the most effective, yet time consuming methods of treatment, are handpicking or cutting the female pupae bags from of the branches. Since this may sometimes be impractical or impossible, there are other methods of treatment to be considered. There are chemical control options available that should be applied during the early instar stages of the caterpillars, typically during June and early July. As with many other pest insects, bagworms are susceptible to predation from parasitoids and birds which can also assist in their control. Now that there has been evidence of these early instar bagworms, it may be time to take action against them.
Bagworms. Photo: Adam G. Dale.
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Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina State University, North Carolina A&T State University or North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact an agent of North Carolina Cooperative Extension.
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