OSU Extension: Magnolia scale abounds

Magnolia scales are native “soft scales. They are called soft scales because the females are hidden beneath a helmet-like soft leathery covering that provides some protection. However, they are easily crushed. Rest easy, magnolia scale only infests members of the magnolia genus. Magnolia scale has the greatest impact on non-native magnolias and associated hybrids compared to native magnolias. Native magnolias are more resistant perhaps because of natural defenses that developed through a shared evolutionary history with the magnolia scale. Non-native magnolias that are most commonly infestationed include star magnolia lily magnolia and saucer magnolia.

Soft-scale adults and nymphs insert their piercing-sucking mouthparts into phloem vessels. They tap plant sap to acquire both carbohydrates which provide energy and amino acids which are the building blocks for proteins and enzymes.

However, the phloem sap holds only trace amounts of amino acids compared to vast amounts of dissolved carbohydrates. This means the scale must process a large quantity of sap to extract the necessary amino acids. They discharge the excess sugar-rich liquid from their anus in the form of “honeydew" which is just a nice name for scale diarrhea.

Magnolia scales are notorious for producing copious quantities of sticky, drippy honeydew. The sugary liquid may cause heavily infested trees to literally buzz with insect activity as flies, bees, and wasps seek a sweet treat. A high percentage of the flies are often members of the blowfly family. Their maggots may have a taste for decaying flesh, but adults like sweets.

The honeydew drips onto the leaves and stems of the host plant as well as understory plants to eventually become colonized by black sooty molds. Although the molds cause no harm to the overall health of infested trees, the blackened leaves can reduce the aesthetic appeal of heavily infested trees.

Life Cycle

Females and males spend the winter as mid-to-late instar dark-colored nymphs attached to the stems of their host plant. Their resemblance to lenticels makes them inconspicuous. The nymphs mature in the spring with the males developing into small gnat-like insects that fly to females and mate.

The females remain immobile, and eggs are produced in late summer to early fall. Like most soft scales, magnolia scale females can produce large numbers of eggs. Numbers ranging from 1,500 to over 3,000 per female are common. This accounts for why populations can build rapidly.

The females are ovoviviparous meaning that eggs are held internally until they hatch creating the illusion that the females are giving birth to the first instar nymphs (= crawlers). Eggs hatch from early August throughout September in Ohio.

The first instar crawlers are highly mobile but become immobile once they insert their piercing-sucking mouthparts into stems. This is the overwintering stage.

As with most soft scales, magnolia scales are seldom direct killers of established healthy trees. However, a substantial loss of sap from a heavy-scale infestation represents a serious loss of energy resources to the trees. The accumulated stress coupled with other stress-producing conditions may cause leaf yellowing and loss, branch dieback and canopy thinning, and even the death of entire trees.

Thus, the best approach to reducing the impacts of these native scales is to first focus on reducing tree stress. For example, maintaining adequate soil moisture by watering during droughts can reduce the impact of a scale infestation. Some stress-inducing issues are preordained such as planting trees in highly compacted soils or in non-irrigated parking lot tree planters.

Although providing proper soil fertility is a vital component of tree health management, fertilizer applications should be used with caution, particularly high nitrogen applications.

Plant selection is also an effective cultural approach to pest management. As noted above, our native magnolia scale has a strong affinity for non-native magnolias and associated hybrids.

Integrated Pest Management (IPM) involves using pest management tactics that fall under the general headings of biological, cultural, and chemical to keep pest populations below an acceptable threshold. Although IPM strategies include the use of chemicals (e.g., insecticides), the graphic below illustrates that cultural and biological tactics should be used first, with chemical tactics held in reserve.

For example, topical applications of pyrethroid insecticides (e.g., bifenthrin) targeting 1st instar magnolia scale crawlers later in the growing season can be effective. However, this chemical class of insecticides is non-selective meaning they can kill bio-allies as well as scale crawlers. Multiple applications may also be required to cover an extended egg hatch which further reduces help from the “biological” corner of the IPM triangle.

Systemic neonicotinoids offer an effective option that minimizes impacts on beneficial insects. Products based on the active ingredients imidacloprid, dinotefuran, or thiamethoxam are effective against these soft scales if applied later in the season to target 1st instar crawlers.

Of course, as with any pesticide, it’s critical to read and closely follow product label directions.

Decapitated Coneflower Heads

The handiwork of the sunflower headclipping weevil (Haplorhynchites aeneus) is just getting underway this season on purple coneflowers (Echinacea purpurea). The damage includes dangling seed heads and stems that looked like soda straws.

The weevil is a well-documented insect pest of cultivated and wild sunflowers (Helianthus spp.) in the Great Plains and will infest other members of the aster family.

The headclipping weevil has reared its ugly snout in recent years in Ohio to become a serious pest of coneflowers in landscapes and naturalized areas. The Shiny weevils range in color from black to copper-brown. They measure a little over 1/4" in length which includes an exceptionally long, curved snout. As with all weevils, this beetle's mouthparts are located at the end of their snout (rostrum). The females insert their snouts into the flower stems to chew a ring of holes around the stem about 1" below the flower head. The flower stem is not completely cut; the damaged stem just breaks-over causing the flower head to hang from the stem on a thin strand of tissue.

Females then lay eggs on the dangling head. Eventually, the flower head breaks from the stem and drops to the ground. Heavily de-flowered coneflower plantings look like a collection of soda straws.The eggs hatch after the flower heads drop to the ground and the weevil's grub-like larvae feed on the decaying flower head tissue. It is speculated that the weevil's odd head-clipping behavior reduces larval exposure to plant defense chemicals and also prevents other insects from competing for the seed head prize.

Mature weevil larvae leave the flower heads and crawl into the soil to spend the winter. Pupation occurs the following spring to early summer and adults appear sometime in late-June to early July. There is one generation per year.

Damage is mainly aesthetic, but the reduction in seed production could potentially cause a significant decline in natural re-seeding. The best method for controlling this weevil is to remove and destroy the dangling flower heads as well as heads that have dropped to the ground. This will prevent weevil larvae from completing their development thus reducing the weevil population for next season.

Insecticides are not a viable suppression option. Insecticide labels will not support making an application to plants in full flower because of the substantial risk of killing plant pollinators. Remember: the label is the law!

Upcoming events

Fairfield Co. Jr Fair Beef Feeder Possession Date & Identification Deadline

• Beef Feeder possession is Aug. 15
• All beef feeder exhibitors will submit the EID 840 tag number by Aug. 20 (within five days of Aug. 15 possession date) to the OSU Extension Office for each beef feeder animal.

With many vegetable gardens in full production now is this time many folks begin to think about food preservation. Did you know you can have your dial gauge canners tested at OSU Extension in Fairfield County? It is very easy to simply call for an appointment at 740-653-5419 and drop off your canner lid. It could be tested while you wait or you can return later and pick up at your convenience. It is important to check dial gauges for accuracy before use each year. Gauges that read high cause under-processing and may result in unsafe food. Low readings cause over-processing. Pressure adjustments can be made if the gauge reads up to 2 pounds high or low. Replace gauges that differ by more than 2 pounds.

Let's Preserve Series – at Keller Market House, 134 S. Columbus Street, Lancaster. Are you planning to preserve summer produce? Join Shannon Carter, Family and Consumer Sciences Educator and Sandy Bohl, instructor, with Ohio State University Extension Fairfield County to learn more. Call 740-653-5419 to register

Dehydrating: Tuesday, Aug. 6, 6 to 7 p.m.

Canning Basics: Tuesday, Aug. 20, 6 to 7:30 p.m.

Let's Preserve Series at Wagnalls Memorial Library

Dehydrating Thursday., Aug. 8, 6 to 7 p.m.

Canning Basics (water bath/pressure) Thursday, Aug. 22, 6 to 7:30 p.m

Registration: Call Wagnall’s Memorial Library to register 614-837-4765Questions: contact Shannon Carter, carter.413@osu.edu or 740-653-5419

This article originally appeared on Lancaster Eagle-Gazette: OSU Extension: Magnolia scale abounds