I have a prolific lawn weed which appears usually in early June (however, early May this year). It first showed up four to five years ago and gets denser every year. Looks like a small dark green leaf clover with small yellow flowers. Vines get "woodier" as season progresses. Usually disappears in late Sept. I have been told it was Japanese clover; however, research mentions this type of clover has purple flowers. Which broadleaf herbicides (homeowner application) are effective?
You have a summer annual, which germinate in the spring and die in the fall. Because of the warm, sunny weather this year we are having a lot of summer annuals establishing early.
Your summer annual is black medic. Summer annuals are hard to control with herbicides because they grow very vigorous through the summer. I would suggest investing in some grass seed. Perennial ryegrass/fine fescue mixture. Apply the seed in September after the weed dies.
If you apply herbicides (3 way broadleaf herbicides - 2,4-D, MCPP and Dicamba) and get control of the weed, if you don't reseed with turf the weeds will only return. Remember the weed will naturally die in September, which is the optimum time to seed or establish turf.
Black medic is also an indicator that you are not applying enough fertilizer, for a quality lawn apply fertilizer 4 times annually (totaling 4 lbs N per 1,000 sq ft), otherwise weeds will dominate.