Question
What are these?
Hello again,
I told my husband about writing you and he wanted me to attach photos. So he found another leaf while raking from our leaf miner infestation and wanted to photograph them and send them to you. Please help, what can we do? We don't like to use chemicals and try to do everything organicly and environmentally friendly but this tree is really testing our patience. Here's a photo of the little grey bugs in the pod.
AnswerThe gall is a very common one on cottonwood trees. It's the Poplar Petiole Gall, caused by the Poplar Petiole Gall Aphid, Pemphigus populitransversus. The aphids overwinter as eggs on the cottonwood's leafless twigs. The eggs hatch in the spring as the leaves develop. When the newly hatched nymphs feed on leaf petioles, they cause galls to form and the small, dark-colored aphids move inside. The aphids secrete a white, waxy material which coats their body. After two weeks, the females bear live young that mature into winged females. These females leave the gall and find plants in the mustard family, where they bear more female, mustard-eating aphids. In the fall, winged forms appear on the mustards, and these fly back to the cottonwoods, where a male and female generation is produced, and then one egg is laid by each female somewhere on a cottonwood twigs, that egg overwinters, and the life cycle begins again next spring.
Infested leaves may drop prematurely in late summer. They are not a serious health problem on Populus spp. and control is not usually necessary for these species.
They can be controlled with the use of a systemic insecticide called bayed Advanced Tree and shrub insect control. This is applied around the tree to the soil in the early spring. The trees roots pick the insecticide up and transport it to the leaves and when the aphid sucks the plant juices from the foliage they are killed. Petiole aphid population may vary greatly from year to year so generally controls are not recommended.
Make sure you rake up all the fallen leaves with the galls and destroy them or move them off site. This will help cut down on next years population.
