The scientific name for the elm leaf beetle is Pyrrhalta luteola. You can recognize an elm leaf beetle by their yellow bodies, and black spots that appear on the beetles head and thorax. Em leaf beetles chew holes into the leaves on an elm tree causing them to turn yellow and brown. This leaves the tree unhealthy and unattractive. The best and most effective method of control for an elm leaf beetle infestation is to use a chemical insecticide.
Pick up an insecticide that contains the ingredient bifenthrin, and read the label thoroughly. Both the University of Colorado, and the University of North Carolina recommend this active ingredient for controlling elm leaf beetles. The label will give you safety instructions, such as wear goggles and a pair of gloves during application.
Place 5 tbsp. of the bifenthrin based insecticide into your backpack sprayer. This insecticide will be in concentrate form, so you will need to mix it with water.
Pour one gallon of water into your backpack sprayer and mix the two ingredients together.
Aim the spray at the underside of the elm leaves and begin spraying. Do this when 75 percent of the leaves have grown, and you see the adults eating and laying eggs. Make sure you spray all of the leaves, and then spray the trunk.
Wait three weeks and give the elm tree leaves another dose of the bifenthrin insecticide. This will ensure that the larvae are also controlled.