Spirea

Plant Identification Photos

Seasonal Pest & Disease Calendar

Pest & Disease Guide (Homeowner-Friendly)

1. Aphids

Symptoms

• Curled or distorted new growth
• Sticky honeydew; ants often present

Treatment

• Strong water spray can remove exposed aphids effectively
• Usually cosmetic unless distortion becomes severe

2. Spider Mites

Symptoms

• Fine yellow stippling on leaves
• Dull or bronzed appearance in hot weather
• Light webbing in severe cases

Treatment

• Hose undersides of leaves during heat waves
• Reduce drought stress; avoid excess nitrogen
• Miticides only if damage is spreading

3. Powdery Mildew

Symptoms

• White or gray powdery coating on leaves
• Most noticeable mid–late summer

Treatment

• Improve airflow and sun exposure
• Avoid heavy nitrogen fertilization
• Fungicides optional and usually cosmetic

4. Leaf Spot / Foliar Blight

Symptoms

• Brown or black leaf spots that may merge
• Premature leaf drop later in summer

Treatment

• Rake and remove fallen leaves
• Avoid overhead irrigation
• Light thinning improves airflow
• Fungicides rarely needed for homeowners

5. Fire Blight (Rare on Spirea)

Symptoms

• Blackened, scorched-looking shoots
• Sudden wilting of young growth in spring

Treatment

• Prune 8–12 inches below infected tissue
• Disinfect tools between cuts (when actively pruning infected tissue)
• Avoid pruning during wet spring weather

6. Winter Dieback / Winter Burn

Symptoms

• Dead branch tips in spring; uneven or delayed leaf-out
• Worse on exposed windy sites and dry winters

Treatment

• Winter watering during warm, dry spells
• Mulch 2–3 inches (keep mulch off stems)
• Spring prune back to healthy wood

Treatment Timing Calendar – Spirea (Colorado Front Range)

March–Early April ( )

• Prune winter damage and old flower stems
• Inspect for early aphid activity

Late April–May ( )

• Monitor new growth for aphids
• Treat aphids only if distortion increases

June ( )

• Begin spider mite scouting as temperatures rise
• Maintain even soil moisture

July–August ( )

• Watch for mites, powdery mildew, and leaf spot
• Treat mites early if stippling is spreading
• Fungicides only if appearance matters

September–October ( )

• Remove fallen leaves (biggest disease reducer)
• Deep watering before soil freeze

Winter ( )

• Winter water during warm, dry stretches
• No pesticide treatments needed

When to Worry vs. When It’s Cosmetic

When to Worry (Action Needed)

• Repeated severe spider mite bronzing/leaf drop
• Major thinning or loss of vigor year over year
• Fire blight symptoms spreading rapidly

Mostly Cosmetic (Monitor Only)

• Light aphids
• Mild powdery mildew late summer
• Minor late-season leaf spotting