Started yard from scratch. limed, starter fertilizer, fescue grass seed and straw. week 1 - grass starts. week 2 -still growing. week 3 -grass tips start to yellow literally overnight. What could it be. At closer examination I noticed new green grass blades were much thinner and smaller than yellow tipped wider blades. Did not look like ‘new’ grass. Is it some sort of weed from the straw? What could it be? Should I be worried?