Insects on Magnolias

Magnolia flowers are pollinated by beetles, not bees.

Magnolias can be tropical or temperate, evergreen or deciduous, but all 80 plus species are known for their fragrant and showy flowers. According to the U.S. National Arboretum, they're easy to grow and don't tend to have many insect pests, but that's not true of all species. Southern magnolias, for instance, are prone to serious insect problems.

Scales

Several scales attack magnolias, including the tuliptree, California red, greedy, oleander and cottony cushion scale, but magnolia scales are one of the worst pests. They cluster on the bottom sides of twigs and can completely cover the branch, if the infestation is serious. The scales excrete a sticky, sweet substance called honeydew that attracts the growth of black sooty mold. Adult females grow to be 1/2 inch in diameter and have dark brown or pinkish-orange bodies that are egg-shaped. Nymphs are dark gray or black.

Leafminers

The magnolia leafminer is also known as the yellow poplar weevil. Both the adult beetle and the larvae damage magnolias. Adult weevils eat leaves and buds while larvae burrow through the leaves, making blotch mines as they feed. Larvae are legless white grubs that grow about .08 inch long. Adults have blackish bodies with a small head and long snout, and grow to be about 3/16 inch. In addition to the blotch mines, infected plants may look faded and develop yellow leaves. Control leafminers by pruning infested plant parts and destroying them. Natural predators like parasitic wasps usually keep populations in check

Caterpillars

The omnivorous looper is a green caterpillar with yellow, green, pinkish or black stripes on its back. It grows to be about 2 to 2 1/2 inches long and damages magnolias by eating all the leaf tissue between the veins. Control caterpillars by handpicking them off the plant.

Aphids

Aphids are small, pear-shaped insects with tubelike structures sticking out of their back ends. They usually feed in groups and damage magnolias by sucking the juices out of the stems, leaves and flowers, causing the leaves to turn yellow, curl or become distorted. Like scales, they produce honeydew, which attracts black sooty mold. Aphids can also spread plant viruses. Control aphids by washing them off plants with a strong stream of water. Prune infested leaves and other plant parts and dispose of them. Avoid using pesticides that kill natural predators like the lady beetle, syrphid fly and lacewing. If a pesticide is necessary, use neem oil or insecticidal soaps.

Hoplia Beetles

Adult hoplia beetles damage magnolias by chewing round holes in the flower petals. These brown beetles look silvery-green in the sunlight and grow to be about 1/4 inch long. Insecticides aren't very effective against them, but you can control them by handpicking them off the flowers and placing them in a pail of soapy water.

Thrips

Thrips are tiny insects with fringed wings that usually don't grow more than 1/20 inch long. Immature thrips look much like the adults, but they don't have wings. The greenhouse thrips, which has a black body with pale wings, is the thrip species that commonly attacks magnolias. Immature thrips of this species have a white or yellowish body. Greenhouse thrips damage plants by extracting plant fluids from the buds and leaves. Symptoms include discolored leaves, tiny leaf scars that are caused when the thrips puncture leaves with their mouthparts, and the appearance of black fecal specks on the leaves. Control thrips spraying them with a strong spray of water to knock them off plants. Prune and destroy infested plant parts. Insecticides are usually ineffective against most thrips, but greenhouse thrips are sluggish and feed out in the open so it's easy to kill them with contact insecticides, like oil.

References

• Fort Valley State University Cooperative Extension: Problems With Magnolias
• University of California Statewide Integrated Pest Management Program: Magnolia
• Penn State Woody Ornamental Integrated Pest Management: Magnolia Scale Fact Sheet
• University of California Statewide Integrated Pest Management Program: Omnivorous Looper
• University of California Statewide IPM: Aphids; M.L. Flint; May 2000
• University of Florida Extension; Leafminers on Ornamental Plants; Eileen A. Buss

Resources

• U.S. National Arboretum: Magnolia Questions And Answers
• University of California Statewide IPM: Hoplia Beetle; E.J. Perry; November 2010
• University of California Statewide IPM: Thrips; S.H. Dreistadt; September 2007