When to Use Horticultural Oil in Florida for Magnolia Scale

Seasonal Treatment

Because of temperature changes, magnolia scales become active and bear young earlier in the year in South Florida compared to the Panhandle. Spraying horticultural oils, especially those with a paraffin-oil base, is best done from January to April. The oil coats the small, youthful magnolia scales and suffocates them. This prevents an increase in adults born later in the long summer. Spot treatment of magnolia scales on magnolia trees can continue into summer and fall, but adult scales will likely persist, even after being doused with the oil solution.

Follow product label directions carefully when applying horticultural oils to magnolias. Products contain different oil formulations and have different effects on plants based on exposure to sunlight or the developmental stage of insects. Horticultural oils may be sprayed onto magnolia scales that line the undersides of leaves in summer but avoid getting the oil spray on the magnolia leaves themselves. The heat and intense rays of the Florida summer sun will scald magnolia foliage wherever the oil spray lands.

Adult magnolia scale insects, which measure up to 1/2-inch long, carry eggs on their bellies as they travel across the branches and leaves of magnolia trees and shrubs. While spraying the adults often doesn't kill them, the oil residue can smother any exposed eggs or newly hatched crawlers. Although some gardeners find it unappealing, simply squishing adult magnolia scales with your fingers is an effective way to diminish the number of bugs on the magnolia and lower the number of subsequent generations. In fall and winter, magnolia scales move from the leaves onto branches to overwinter.

Contact your county's University of Florida cooperative extension office and speak with a horticultural agent about using horticultural oils to control magnolia scale. Certain brands of horticultural oils are appropriate for use in summertime, and adult female scale insects lose their protective waxy coating just before they lay eggs. Therefore, repeated use of horticultural oils year-round can both prevent and rid infested magnolia plants of the scales with diligence and careful application.