Sweetbay Magnolia - What is wrong? - Ask Extension
I planted this sweetbay magnolia last fall. When it leafed out this spring, some of the leaves were curled and now some look like they have bug damag...
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Sweetbay Magnolia - What is wrong? #878305
Asked July 22, 2024, 3:48 PM EDT
I planted this sweetbay magnolia last fall. When it leafed out this spring, some of the leaves were curled and now some look like they have bug damage also. Early in the spring, I did treat some of the lesser celandine in the area of the magnolia with Round Up. Used a small paint brush and painted just the lesser celandine leaves. Could there have been herbicide run off that affected the magnolia? Anything I can do to help the sweetbay?
Baltimore County Maryland
Expert Response
The minor amount of insect damage pictured was caused by a native insect called the Magnolia Serpentine Leafminer Moth. It does not cause significant injury to the plant and can be ignored.
The other leaf discoloration and deformities do look like herbicide damage, though we aren't certain it's from the Roundup application from months ago, especially since it sounds like you weren't using a lot of the chemical. This may depend on what was in the Roundup used, though, since only some of the formulations use glyphosate (the ingredient best used on Lesser Celandine). Some Roundup formulations use different herbicide ingredients, or may combine glyphosate with others. We would not expect non-excessive levels of glyphosate to have affected the Magnolia unless it was accidentally applied to the trunk or surface roots. (Once glyphosate residues contact soil, they bind to it well and are not likely to move into other plants or contaminate stormwater unless there is soil erosion that carries the residues with it.) Other herbicide ingredients, though, can more readily affect nearby trees and shrubs, either via the soil or as airborne (volatilized) chemical, especially if applied on a warm or breezy day.
While we can't determine the exact source of exposure, any herbicide damage to a tree is untreatable, in the sense that the plant will either grow out of the damage eventually on its own (if exposure wasn't too great), or it will permanently be stunted or decline if the impacts were too great. Time will tell how the tree fares, and for now, you may want to plan on trimming off the branch tips with symptomatic foliage this coming winter/spring. (You can probably do it now, but generally pruning should be avoided from late summer into autumn.) Leaves cannot heal from damage (from any source, insect, infection, or chemical), though subsequent new foliage no longer under the influence of herbicide may grow normally. However, the branches themselves were probably impacted as well, which means new leaf buds that grow on the branch tips that are currently bearing deformed leaves may also either not develop properly or not develop at all, hence the recommendation to prune them back to healthy-looking growth.
Miri
The other leaf discoloration and deformities do look like herbicide damage, though we aren't certain it's from the Roundup application from months ago, especially since it sounds like you weren't using a lot of the chemical. This may depend on what was in the Roundup used, though, since only some of the formulations use glyphosate (the ingredient best used on Lesser Celandine). Some Roundup formulations use different herbicide ingredients, or may combine glyphosate with others. We would not expect non-excessive levels of glyphosate to have affected the Magnolia unless it was accidentally applied to the trunk or surface roots. (Once glyphosate residues contact soil, they bind to it well and are not likely to move into other plants or contaminate stormwater unless there is soil erosion that carries the residues with it.) Other herbicide ingredients, though, can more readily affect nearby trees and shrubs, either via the soil or as airborne (volatilized) chemical, especially if applied on a warm or breezy day.
While we can't determine the exact source of exposure, any herbicide damage to a tree is untreatable, in the sense that the plant will either grow out of the damage eventually on its own (if exposure wasn't too great), or it will permanently be stunted or decline if the impacts were too great. Time will tell how the tree fares, and for now, you may want to plan on trimming off the branch tips with symptomatic foliage this coming winter/spring. (You can probably do it now, but generally pruning should be avoided from late summer into autumn.) Leaves cannot heal from damage (from any source, insect, infection, or chemical), though subsequent new foliage no longer under the influence of herbicide may grow normally. However, the branches themselves were probably impacted as well, which means new leaf buds that grow on the branch tips that are currently bearing deformed leaves may also either not develop properly or not develop at all, hence the recommendation to prune them back to healthy-looking growth.
Miri
