Tips for Managing Magnolia Tree Scale Infestations

magnolia tree sap on car

Are you dealing with heavy dripping sap from your magnolia trees? You’re not alone. This summer, Michigan residents experienced a common problem: magnolia scale infestations causing excessive sap production. Many concerned homeowners wondered if it was time to cut down their trees and start fresh. But fear not! In this article, we’ll explore effective measures to manage magnolia scale infestations and revive your beautiful magnolia tree.

Understanding Magnolia Scale Infestations

Magnolia scale is a type of sap-feeding insect that causes serious damage to magnolia trees. When these insects feed, they excrete sugary sap, resulting in a sticky mess on leaves, branches, and everything beneath the tree. The sap also attracts sooty mold, which turns the leaves black. Moreover, the loss of sap can lead to yellow, stunted leaves and dying branches, and chronic infestations can eventually kill the tree. The star magnolia (Magnolia stellata) and the saucer magnolia (Magnolia x soulangiana) are particularly susceptible to scale infestations.

Effective Management Strategies

Successfully managing magnolia scale infestations requires understanding the insect’s life cycle and targeting vulnerable stages. Magnolia scale has one generation per year, with eggs hatching late in the summer. The young nymphs, also known as crawlers, emerge from under the female scales and spread along branches in search of a feeding site. It is during this crawler stage that control measures can be most effective.

Accurately timing pesticide applications is crucial. Contact insecticides such as horticultural oil or insecticidal soap are recommended, as they can reduce scale infestations. It is important to note that the nymph stage is more vulnerable to pesticide control measures than the adult scale, which has a protective covering. By using the growing degree days (GDD) information provided by the Tips Tree Planting website, you can determine the optimal timing for these applications.

Timing is Everything

The MSU Integrated Pest Management website offers specific GDD data to predict the hatch of magnolia scale. According to the website, the peak hatch of magnolia scale occurs between 1,925 and 1,950 GDD. By utilizing this critical information, you can accurately predict when the magnolia scale crawlers will be active on the foliage and branches, allowing you to time your pesticide use effectively. This approach not only increases the effectiveness of the treatment but also reduces unnecessary applications and eliminates the need for following a fixed annual pesticide schedule.

The Power of Enviroweather

Michigan State University’s Enviroweather website plays a vital role in managing magnolia scale infestations. With a network of weather stations across the state, Enviroweather provides localized data on temperature, including GDD. By monitoring daily air temperature measurements, you can determine insect development stages and pinpoint the optimal time for pesticide application. This website is an indispensable tool in reducing the impact of pests like magnolia scale on trees throughout Michigan.

For example, in Flint, Michigan, the local weather station recorded peak magnolia scale hatch occurring between August 16 and 17 in 2019, while the previous year experienced a peak hatch 10 days earlier. In Traverse City, Michigan, the growing degree days reached the threshold for magnolia scale hatch on September 10, 2019. Thanks to these localized weather stations, you can accurately predict critical stages for scouting and effectively managing magnolia scale infestations.


Don’t let magnolia scale infestations ruin the beauty of your magnolia trees. By understanding the insect’s life cycle, timing your pesticide applications correctly, and utilizing resources like Enviroweather, you can effectively manage these pests and restore your trees to their former glory. Stay vigilant, and with the right strategies in place, you’ll keep your magnolia trees healthy and thriving.


  • Herms, D.A. “Using degree days and plant phenology to predict pest activity.” Chapter 11, IPM of Midwest Landscapes: Tactics and Tools for IPM.