Question
Should the yellow day lillies be dead headedd to get more bloom?

Answer
Hi Marilyn,
Thanx for your question.  It sounds like a fungus to me.  You didn't say where your lived.  In the U.S., many plants react differently to their climate.  Many have been introduced to different parts of the county to which they plants are not native. Black-eyed Susans like hot, dry weather, but they like to be watered at least once a week and don't spray water on the leaves as this will increase fungal infection.  Don't allow the plants to grow too close together because this will result in a fungal infection.  I hope this helps.  If it doesn't, please post a follow-up.
Tom