Diagnosing Sudden Yellowing in Established Althea (Rose of Sharon)

Symptoms and Possible Causes

An 8-foot althea in Fort Worth, TX, flowered well for 2–3 weeks, then leaves turned bright yellow and wilted, spreading to 35–50% of the canopy. A nearby althea is unaffected. Recent Miracle-Gro application preceded symptoms. Mid-90s temperatures, sprinkler twice weekly plus hand watering.

Three Likely Causes

• Insect Infestation: Check leaf undersides and bark for whitefly, aphids, or scale. Treat with appropriate insecticide if found.
• Bacterial Leaf Blight or Canker: Vascular diseases requiring professional trunk injection (Mauget, Wedgel, Arbortec systems).
• Fertilizer Burn: High-nitrogen Miracle-Gro in extreme heat can scorch roots.

Recommended Action

Inspect for insects first. If none, consult a certified arborist for disease diagnosis and injection treatment. Stop high-nitrogen fertilizing. Deep water to flush salts. The unaffected nearby plant suggests a localized issue, not site-wide.