Answer: The yellow spots may have to be raked out so the healthy grass can creep into the areas where you used weed killer. Korean Grass, also called Zoysia, is sensitive to herbicides, as you've discovered. You can take small plugs or sprigs from healthy areas and transplant them into the damaged areas to help things fill in a little faster.
Zoysia requires a moderate level of nitrogen fertilizer to maintain a dense turf and a deep green color. Fertilize 2-3 times during the growing season, using a ratio of 3-1-2 (nitrogen, phosphorous, potassium). Each application should provide about 1 pound of nitrogen per 1,000 sq. ft. of area. Applications should be made in late spring, early summer, and fall. In areas where zoysiagrass remains green year around, frequent applications of soluble nitrogen fertilizers will help maintain a green color during the cool season (usually pound of soluble nitrogen per 1,000 sq. ft. per month from October through March will suffice).
Best wishes with your turfgrass!
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