These photos were sent to me by Deborah Lakowicz Dramby, a graduate student in the College of Agriculture and Natural Resources. Along with other UM students she helped create the Public Health Garden at the School of Public Health- http://publichealthgarden.blogspot.com/ Here's a shot of the Salad Table they constructed last fall.
A student crew was getting the garden ready for planting when they came across sow thistle and burdock plants covered with aphids (probably sow thistle aphids)- a fairly common sight.
The plants were pulled and bagged to prevent movement of these sucking insect pests to lettuce plants. If the infestation had been less severe the plants could have been left in place to serve as food for predators (lady bird beetles, hover fly larvae, lacewing larvae) and wasp parasitoids.