We suggest drenching their ground nest entrance hole with Demon WP during the evening. Yellow Jackets return to their colony at dusk and are less likely to attack at night. Demon WP comes in foil packages that have 4 soluble packages inside. Mix two of the soluble packages per gallon of water into a bucket or large watering can. If you can cover the entrance hole with screen do so right before quickly pouring the Demon solution down their hole. If you are unable to locate the ground nest location we suggest setting out Yellow Jacket traps. Yellow Jacket traps will lure very large numbers of these insects that can then be destroyed  after they are trapped. Yellow Jacket traps are reusable, we also stock the attractant to place into the traps.