m0useanswered grow question 3 years ago That to me looks like a trichome that lost its head.
but this reference says it is a unicellular non-giandular trichome
https://resize.mantisadnetwork.com/mantis-ad-network/image/fetch/w_500,q_75,c_limit,f_jpg/http://uploads.medicaljane.com/wp-content/uploads/2017/03/trichomes3.jpg
This is what a close of of powdery mildew looks like.
https://www.dinafem.org/uploads/oido5_blog_full.jpg
I don;t think you have anything to worry about here
Best of Luck and Happy Growing!