|What do I use to rid my lawn of a white powdery substance on part of the lawn?|
|I suspect you are seeing a common fungal disease called "Powdery Mildew" which is found during cool, humid weather and in shady areas. The disease is usually most common in spring and fall, but can occur anytime during the growing season.
Grass which is affected may turn yellow and die as the white powder covers the green leaves and prevent the grass from photosynthesizing. You can test for this by rubbing a piece of grass blade between your fingers. If the white powder rubs off on top your hands, it is powdery mildew.
Mildew can be prevented by pruning shrubs and trees (limbing them up) to allow more sun to reach the grass, and improve air movement.
You can also implement good sound practices to improve overall health and vigor of the grass by fertilizing in late spring, early fall and late fall; by mowing the lawn frequently at approximateyl 2.5-3.5" tall; and by watering infrequently but watering deeply when you do water.
Hard, compacted soils can be loosed by core aerating the lawn every 2 years.
Best wishes with your lawn.