i had this problem with my twin's baby pine tree that turned 4 this year, and it was covered. i read an online recipe, decided to add an extra kick, and they dropped like flies upon spraying.

INGREDIENTS
-2 tablespoons of dawn dish soap (preferrably bleach dawn)
- 1 tablespoon of spic and span floor cleaner
-quart mason jar
- water

put the soap and spic and span on the bottom of the jar and swirl in the bottom until it is a mixture of soapy awewsomeness. then, fill the quart jar up with water and mix it with a spoon. transfer it to a spray bottle, and spray lightly in the affected area, upon spraying, they should drop like flies. the chemicals will finish off the survivors. if there are some left, spray again. you'll also want to water your plant well during and after the elimination process until the affected areas begin to heal.
Hope this helped!
love,
bug_killer97, your thirteen year old exterminator.