Why Are My Hybrid Poplar Trees Losing Their Leaves So Early?
The poplar family includes aspens, cottonwoods and silver and Lombardy poplars, as well as some hybrid poplars that have more resistance to disease and insect pests. All poplars are fast-growing but short-lived trees, prone to trunk rot, winter damage and disease problems. Leaves dropping prematurely may indicate a minor fungal problem or the early signs of the tree's demise. Positively identify the problem and watch the tree closely. Does this Spark an idea?
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Disease
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Several fungal diseases including leaf spots and cankers affect hybrid poplars and may cause early defoliation. Look at the leaves for brown or yellow spots or marks. Look at the tree itself for black or brown cankers. These diseases are most prevalent following cool, wet weather, but may occur at any time. They are most damaging when the tree is defoliated midsummer. Cut out branches with cankers and remove the fallen leaves because the disease spores overwinter in them. Water trees early in the morning so the leaves dry quickly, and plant trees so air circulates freely. Spray the trees in spring when leaves bud out with mancozeb chlorothalonil or basic cupric sulfate and make three additional applications, spaced 12 to 14 days apart.
Insects
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Aphids, mites, midges and wasps infest poplars and may cause early defoliation. Look for signs of infestation, such as honeydew, a sticky substance secreted by aphids, or large numbers of ants that feed on the honeydew. Remove a leaf and cut open the tender area at the base of the leaf. You may find insect larvae inside the leaf. Examine the poplar for galls, or bumps, that grow on the leaves and bark. Insects feeding on the plant cause these galls. Unless the defoliation occurs in midsummer, the tree will likely recover. Rake up the leaves and destroy them, and spray the tree next spring with horticultural oil to destroy overwintering insects.
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Herbicide Drift
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Poplars have shallow roots that spread through the top layer of the earth, making them very susceptible to damage from herbicides. Curling, distorted or dropping leaves are a typical symptom. If you suspect herbicide damage, continue caring for the tree as usual. The tree will likely recover within a few weeks.
General Recommendations
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Watch the hybrid poplar trees the following spring. If the leaves do not return, the trees are probably dead. Remove them immediately to prevent property damage or personal injury. Most poplar trees only live 20 to 30 years before succumbing to disease, insect infestations or trunk rot.
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References
Resources
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