Q.zoysia looking thin and yellow
Why is my Jamur zoysia pretty green and thick in some areas and thin and yellow colored under oak trees? Near the street and outer edges, sod looks great but in a wide circle around 25 year old oak trees, the sod is yellowing and thin – can see dirt. The trees have vinca ground cover in a circle extending about 10 feet out from the tree trunk. The sod that is next to ground cover up to house looks bad. Sod was planted in spring of 2014 and was lush and green until this June when it started looking thin and yellow.
The yellowing and thinning of your lawn is likely to the invasive Vinca roots.
The Vinca may be taking up the water and soil from the Zoysia.
You can try to add a bit of water to the stressed lawn.
You may have to choose a less invasive ground cover for under your Oak Tree.
Here are a few links for you.
https://www.gardeningknowhow.com/ornamental/groundcover/periwinkle/periwinkle-control-methods.htm
