Knowledgebase

Top leaves on Magnolia tree turning brown #679192

Asked January 19, 2021, 4:07 PM EST

We have recentlhy noticed that the leaves at the top of our magnolia tree are turning brown. Is this a disease or just something to be expected in winter. These are not deciduous magnolias.

Montgomery County Maryland

Expert Response

If this is a Sweetbay Magnolia (Magnolia virginiana), leaf browning over the winter is normal, as they are only semi-evergreen in our area and their leaf retention depends on weather and site exposure. As trees age, they might retain more leaves than younger trees, though this will still depend on the tree's genetic makeup (subspecies australis tends to be more evergreen, for example) and its location in relation to windbreaks. In spring, browned foliage will shed when new foliage is about to or has just emerged. Mild autumn weather can encourage late-season growth on some trees, and this tissue does not have time to adequately prepare for winter conditions and is usually the first to succumb to damage.

If this is a Southern Magnolia (Magnolia grandiflora), leaf browning of upper, younger growth could be a sign of inadequate water or root decline due to overly-wet conditions. "Winter burn" is a phenomenon that causes tissue desiccation in times of dry and/or very cold or windy weather, when the plant can't replace moisture lost to evaporation from sun, wind, and low humidity. Overall, we haven't had a measurable amount of those conditions yet this winter, so while possible, this is less likely. Winter-burned foliage is shed in spring as new growth emerges, and often despite having a haggard appearance for the time being, the plant emerges relatively unscathed.

Evergreen plants depend on accessible soil moisture to keep their leaves hydrated during winter; while they aren't photosynthesizing much (if at all), moisture can still be lost as leaves "breathe" through pores in their tissues, especially in windy conditions that whisk humidity away. Soil moisture that is frozen is inaccessible to roots, so using a thicker layer of mulch (around 3" depth) over a plant's root zone will improve insulation and help avoid this for more drought-sensitive plants like Azaleas, Boxwood, Camellias, and Magnolia. When the soil is thawed, checking it periodically for moisture levels (just as in summer, a few inches beneath the surface) and watering as needed can reduce the risk of winter damage to evergreens. This winter hasn't been very dry, but some areas might be drier than others based on local weather patterns and how water-retentive the soil is in the garden.

Roots that are too wet also contribute to drought symptoms in foliage, and this can include winter burn in the dormant season. When roots stay too wet for too long after rainfall/irrigation, the soil pores stay saturated and not enough oxygen can infiltrate the soil as it normally would; roots need gas exchange in the soil to "breathe" as well and will die back or become infected by opportunistic pathogens if suffocated. When roots die or cease to function properly, the plant loses its ability to stay hydrated, and foliage desiccation ensues. To avoid this, site plants in well-drained locations unless they are adapted to such conditions, water only when needed, and correct any drainage issues that arise such as flooding from drain pipes/outlets and changes in soil grade that directs water to its root zone. While both Southern and Sweetbay Magnolias have above-average tolerance for wet sites (the latter especially so), it's possible it received too much water at some point in the past few months.

Pests and diseases are relatively few for Southern Magnolia, but you can check the young stems and leaf undersides for scale, a sap-sucking pest that occurs on Magnolia. They will look like immobile lumps on the bark or foliage and be white, gray, or brownish in color. Treatment will have to wait until the warmer months; https://extension.umd.edu/hgic/topics/soft-scales-trees-and-shrubs

If you do not see any scale and symptoms don't seem to match issues with winter burn, feel free to send us photos of the tree for assessment. Trunk damage from antler-rubbing deer or cuts from lawn equipment can also compromise a tree's health and result in direct dieback or trunk infection, either of which can impact the youngest upper growth first.

Miri

Loading ...