How to Get a Lush, Green Lawn Your Neighbors Will Envy
How to Get Rid of Springtails
One of the most effective ways to control springtails is to dry out the infested area. Springtails require a high-moisture environment to breed and thrive, living mostly off of algaes that grow in moist conditions. They will either leave the infested area or die out. If there is an infestation that cannot be controlled by drying out the infested area, use an appropriately labeled insecticide with a residual time These will typically be a liquid concentrate form, a wet-able powder form, or a dust product. DO NOT APPLY UNTIL AREAS ARE DRY. If area will not dry naturally, use Corn Starch to soak-up any lingering moisture and otherwise 'steer' any rain water or irrigation away from area.
Also, if there is a noticed springtail infestation around the perimeter of the structure, use the insecticide to do a barrier treatment and apply corn starch to reduce or eliminate moisture. Caulk and seal all cracks and crevices and inspect potted plants before they are brought into the house.
I would talk to your local lawn and garden supply store (or mill and feed) - NOT a box store or hardware store. There are also selective grass control chemicals. YOu can research this by Googling using search string "Tall Fescue Control" - there are lots of articles by the USDA and individual state cooperative extension services.
There is a treatment called chlorsulfuron TFC (Tall Fescue Control) that will do this - it worked for me in western New York, but took 3 years to finish out all the tall fescue. It may now be limited to use by commercial applicators - pretty potent stuff. Can yellow bluegrass or make it phytosensitive, but our looked OK during treatment because the TFC was applied in the fall for best results, and our lawn was dormant till spring anyway.
Tall fescue can also be controlled by real short mowing, but only in areas where the bluegrass is dominant and really thrives so will eventually crowd out the trimmed fescue, but you may be too far north for that.