Lawns deficient in nitrogen are very suseptible to rust and red thread fungus diseases during the cool months of spring. By March, most plants are their peak of growth. This includes weeds. Dandelions are growing everywhere. If your neighbor has dandelions, you will have them too.
Broadleaf weeds are easy to control with spot spraying.
Be careful when using Dicamba near shallow rooted trees and shrubs. It can be absorbed through the roots and damage the plant. Oxalis is not controlled by those commonly available herbicides, but there is help. You may need to ask your gardener to apply it for you. Remember, gardeners must be licensed by the State of California to apply pesticides for their customers.