Diagnosing Yellow Patches in a Northeast Lawn: Zoysia Dormancy or Fungal Disease?

Two Likely Causes

1. Zoysia grass: Popular in some Northeast areas but turns yellow/brown in cool weather. You'd likely know if you have it.
2. Cool-season grass with fungus: Cool, wet fall/spring triggers powdery mildew (Erysiphe graminis) on bluegrass/fescue. Symptoms: yellowing, thinning, white powdery coating. University of Minnesota details this.

Management

• Turn off sprinklers now. Grass doesn't need water in fall/winter (unless in deep South). Excess moisture fuels fungus.
• Avoid over-fertilizing. Excess N weakens grass, invites disease. Use slow-release organic N: blood meal, alfalfa, Milorganite, manure.
• Grubs are good. They attract birds that eat them. Chemicals repel birds, causing grub explosions.

Best Action

Do nothing aggressive. Cold weather will kill fungus naturally. Save money—skip the TV-advertised products. A steak dinner is a better investment.