Golden-yellow leaves on a Carolina poplar (Populus x canadensis) hail autumn’s arrival as trees ease into their winter dormancy. When yellowing leaves occur throughout the active growing season, however, it signals trouble. Environmental stresses, nutrient deficiencies, insects and diseases often make their presence known through Carolina poplar’s foliage. As normally green leaves turn yellow, this discoloration may occur as stippling, splotching, marginal marking or entire leaf color change.
Just as in human family trees, botanical families are also prone to genetic health predispositions that they inherit from parent lines. Carolina poplar is a hybrid cross between two botanical parents -- the Eastern cottonwood (P. deltoides) and the European black poplar (P. nigra). Its susceptibility to the same insects, diseases and environmental stressors as other Populus species helps identification of these problems. Common family weaknesses exhibit common signs and symptoms as trees progress through stages of distress.
Chlorosis occurs when chlorophyll reduction causes naturally green leaves to turn yellow. This may be caused by excessive use of chemicals through insecticides or fertilizers, insufficient drainage, root compaction or nutrient deficiencies. The University of Illinois Extension cites iron, manganese and zinc deficiencies as common contributors to chlorotic leaves. Iron chlorosis begins spreading on outer (younger) leaves and moves to inner (older) leaves. Manganese and zinc chlorosis attack older leaves first, moving from the inside of trees outward.
The University of California identifies numerous insects that plague Carolina poplar. Although small populations of aphids do not usually damage trees, heavier infestations cause leaves to turn yellow. As they feed, scale insects can also cause yellowing leaves that drop prematurely. Leaf miners, which are larval forms of some moths, make golden furrows in leaves as they tunnel through leaf tissue, and they can also create entire yellow patches on leaves. Maintaining tree health through sufficient irrigation is vital to strengthen poplar trees against insect predators.
Insects not only create primary problems for poplars, but they are important secondary offenders that compromise tree health. As vectors for disease, insects that travel from plant to plant are capable of spreading disease and decimating entire tree populations. Fungal diseases, rusts and cankers can cause yellow leaves on Carolina poplar. Poplar rust caused by the fungal pathogen Melampsora medusae may be fatal to young trees that are not strongly established, but it rarely causes fatalities in older trees. Marssonina and Septoria leaf spots are common fungal diseases that attack poplars. Following a scrupulous sanitation regimen of raking fallen leaves in autumn from around Carolina poplar prevents fungal pathogens from overwintering in leaf litter and re-infecting trees in spring.
- University of Illinois Extension: Focus on Plant Problems -- Chlorosis
- University of California IPM Online: Poplar, Cottonwood and Aspen -- Populus spp.
- University of Idaho: Poplar Rust Caused by Melampsora Medusae
- University of Minnesota Extension: Leaf Spot Diseases of Poplar
- University of California IPM Online: Aphids
- University of California IPM Online: Foliage Miners
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