Greenhouse Rose Sepal Tip Burn: Chemical Fume Damage

A rose consultant in Zimbabwe reports purplish sepal tips dying back as flowers open on greenhouse-grown roses and hypericum. Fixed ventilation, heater use suspected.

Diagnosis: Sulfur Dioxide / Heater Fume Toxicity

Sepals are the first tissue affected by low-level chemical fumes. Research confirms sulfur dioxide pollution—and even standard greenhouse heater exhaust—causes characteristic purpling and dieback of sepal tips only. Chlorinated water can produce similar symptoms.

Differential: Downy Mildew

Downy mildew causes purpling too, but primarily on leaves (which twist and distort), not isolated to sepal tips. If leaves are clean, it's not downy mildew.

Remediation Steps

• Ventilation: Increase air exchange—install fans or open vents during/after heating
• Heater maintenance: Ensure complete combustion; consider vented heaters
• Water testing: Check chlorine levels; dechlorinate if necessary
• Monitor: Sepal tip burn is cosmetic—flowers still marketable if mild

This is an environmental issue, not a pathogen. No fungicide will help. Fix the air quality, and new growth will be clean.