Zoysiagrass is a warm-season grass that grows well in the southern United States from spring until fall. Well-maintained, healthy Zoysia is thick enough to crowd out most weeds, but oak seedlings will sprout from acorns in zoysia. This is especially true under oak trees, where the shade of a parent tree leads to patchy zoysia growth patterns. To prevent the sprout of oak seedlings, rake the grass to remove acorns as they fall. Once the acorns have sprouted, you will need to take other measures.
Pull out the smallest trees by hand. Get as much of the root as you can to prevent the tree from returning.
Mow over oak seedlings with a lawn mower as you mow your grass. Repeated mowing will kill oak seedlings by removing their top growth.
Cut off the tops of larger oak seedlings that are too big to mow with a pair of branch loppers. Position the loppers at ground level to remove enough of the woody stem that it does not become a future problem when mowing.
Paint the exposed stems of oak seedlings with a systemic herbicide containing glyphosate. Systemic herbicides will be absorbed into the plant's vascular system and kill the oak seedling at the roots.
Treat your grass with an application of a broad-leafed herbicide. A broad-leafed herbicide will kill oak seedlings but leave grass unharmed. Pour the herbicide into a spray applicator. Prime the pump of the applicator by grasping the pump handle and working it up and down until pressure builds. Hold the spray tank in one hand and the spray wand in the other. Activate the trigger on the wand to release a fine mist. Pass the spray over your lawn in sections to kill the seedlings.