The magnolia tree, with its magnificent blooms, has been flowering on Earth for tens of millions of years. Magnolias are found throughout the world, widely planted and prized for their ornamental value, shade and wood. Luckily for home magnolia growers, the trees have few problems with pests and diseases; the same holds true for magnolia flowers. Even better, problems are seldom fatal to the tree.
You know an insect is something to watch out for on a prized plant when the pest's name includes the name of the tree. Such is the case with the magnolia leafminer, a weevil that begins its feast by dining on a magnolia's flower buds, moving on to leaves. As it eats through vegetation, the insect leaves oval holes behind.
The best way to control leafminers is to remove plant debris like fallen leaves, especially before spring. Leafminers overwinter in the litter. Try not to use insecticides, since the chemicals will likely kill fellow insects such as wasps, which serve as leafminer predators.
With a wide range of plants in its diet, Bevipalpus californicus is called the omnivorous mite in the United States. Arachnids like the omnivorous mite are called false spider mites, too, because they don't create webs. Injecting toxic saliva into the magnolia's flower buds as it feeds, the omnivorous mite stunts growth and creates necrotic areas.
Check for these areas of death on the bottoms of leaves along with the flat, red mites. The pest also leaves a white molted skin behind. Control with sprays, seeking advice from your extension agent.
The hoplia beetle only likes to eat magnolia's flowers, but only as an adult. The beetle's early life is spent in the larval stage in quiet, undisturbed places, feeding on ground litter and plant roots. In spring the beetle emerges and flies to light-colored flowers, including magnolia blooms, chewing holes in the flowers. The brownish red beetle is easy to see, especially in the sun where it looks an iridescent silver-green.
To get rid of hoplia beetles, pick them off and put them in buckets filled with soapy water. The University of California Integrated Pest Management Program says that filling 5-gallon buckets with water and a bit of detergent might serve to attract the beetles away from the flowers and into the bucket, thereby helping to reduce the hoplia beetle population in a magnolia tree's vicinity. Insecticides aren't effective.