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Diagnosing Spots on Agave: Scale, Edema, or Fungus?

Diagnosing Spots on Agave: Scale, Edema, or Fungus?

An agave in a well-drained cactus bed (Zone 9b, Orlando) developed spots 3 weeks ago. Other 20+ succulents are healthy. Dry weather recently.

Agave with spots

Whole agave

Close-up of agave leaf spots

Leaf close-up

Differential Diagnosis

Condition	Signs	Likelihood
Scale insects	Small, round, waxy bumps on leaves; can be scraped off; honeydew/sooty mold may be present	High
Agave edema	Water-soaked, blister-like spots from overwatering in heat; usually on lower leaves	Low (no watering)
Fungal leaf spot	Irregular lesions with halos; rare in dry, well-drained conditions	Low
Hail/freeze damage	Physical pitting; unlikely in Orlando	Very low

Recommended Treatment

Horticultural oil (lightweight/summer oil): Spray thoroughly to smother scale. Repeat 3× at 7-day intervals.
Add neem oil to the mix for broader pest/fungal coverage.
Do NOT use vegetable oil or dormant oil (too heavy, can burn).

If No Improvement in 2–3 Weeks

Consider removing the plant to protect the rest of the collection. Sometimes one plant is a persistent reservoir.

Monitor new growth—clean leaves indicate success.

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