Blue Substance on Grass Blades: Fungal Disease Identification and Treatment

Likely Cause: Phytopathogenic Fungus

A homeowner saw "blue stuff" on grass blades and worried about child safety. The expert identified it as likely a turfgrass fungal infection.

Diagnostic Resources

• Texas A&M Plant Pathology - Lawns & Turf – disease descriptions, images.
• Brown Patch Disease Info – specific common fungus.

Conditions Favoring Fungal Outbreaks

• Heat stress + high thatch + overwatering.
• Poor aeration, excessive nitrogen, evening watering.

Immediate Actions

• Clean tools/mower: Bleach solution to prevent spore spread.
• Reduce thatch: Core aerate, compost removed thatch.
• Adjust watering: Deep, infrequent, morning only.
• Lower nitrogen: Avoid late-season fertilization.

Treatment Options

• Fungicides: Benomyl, thiabendazole, thiophanate-methyl, quintozene.
• Iron sulfate: ¼ oz per ½ gallon water per sq. yd.
• Genetic upgrade: If persistent, renovate with fungus-resistant hybrid cultivars.

Safety Note

Most lawn fungicides have low mammalian toxicity when applied per label. Keep children/pets off until dry. Blue-green spores themselves are not typically toxic but indicate active infection needing management.