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I N S E C T S
All species of poplars are affected by some sort of leaf-feeding caterpillar. Larva feed on the buds or the leaves causing a lacy appearance. Infestations usually aren't fatal, but several successive years of attack can weaken a tree enough to kill it. Insecticides can be effective to treat infestations.
Leaf beetles from the species Chrysomela can cause substantial damage to poplars in urban settings. After spending the winter in the bark or other shelter, the adult beetles emerge in the spring and feed on the leaves and twigs. Females lay yellow eggs on the underside of the leaves and the larva then also feed on the leaf tissue between the veins. Insecticides can be effective, but because four or more generations of the beetles occur each year, multiple applications in a single year may be necessary.
Cottony Cushion Scales and Mealybugs
White, cottony masses covering leaves, stems and trunk is an indication of cottony cushion scales or mealybugs. The two insects are very similar and they are quite common. Pale yellow or reddish larva feed throughout the summer on leaves stem and trunk. They excrete honeydew which often becomes black. When white egg masses completely cover leaves and twigs, dieback can occur. Insecticides can be used to kill the larva, while a dormant spray can be used to kill overwintering adults.
Poplars can be infested with many types of scale insects which settle on the leaves, twigs, and trunk. Small and soft-bodied, the young feed by sucking sap from the tree. Their legs atrophy and a hard crusty shell develops around their bodies. To control them, use insecticide for the active young and a dormant spray for the overwintering adults.
This weevil (Cryptorhynchus lapathi) affects many species of poplar as well as all species of willow. Although the adults cause some damage by chewing holes in bark and twigs, the major damage is caused by the white larva which burrow into and feed on the inner bark. Large quantities of sawdust known as frass are expelled from the holes. This activity disrupts the water-conducting system of the tree and weakens branches. Infected trees should be removed to prevent further spread.
Poplar Petiolegall Aphid
Galls forming on the leaves of poplars are caused by the Poplar Petiolegall Aphid (Pemphigus populitransversus). Although the galls are unattractive, they do not cause serious damage to the tree. In summer, the galls produce winged aphids which fly to vegetables such as lettuce and beets to feed on the roots. In the fall, they return to the poplar to lay eggs. In winter, a dormant spray can be effective in controlling these aphids.
D I S E A S E S
Wetwood, or Slime Flux
A bacterium (Erwinia nimipressuralis) takes hold in the heartwood and causes abnormally high sap pressure. Fermented sap (or flux) is forced out of wounds or cracks in the tree. The flux is sour-smelling and oozes down the side of tree, causing unsightly gray streaks when dried. The wounds generally will not heal properly and the condition can persist for many years. Although there is no treatment for the disease, the streaking can sometimes be prevented by placing a small tube in the infected area so the flux drips away from the tree.
Canker and Dieback
Canker and dieback on poplars is caused by several different fungi. Lombardy poplars are especially vulnerable. Dark sunken cankers form where the fungus enters a tree through wounds or cracks. These cankers can disrupt water and nutrient flow and, if it spreads to more than half of the diameter of the trunk, will probably kill the tree. Pruning off infected branches and removing severely infected trees can slow or even prevent spread. The best measure is to promote the general health of the tree through regular fertilization and watering.