African Milk Tree with Fire Blight? Rare but Treatable
Euphorbia trigona
Fire blight is a highly destructive and contagious bacterial disease caused by Erwinia amylovora. It primarily affects plants in the Rosaceae family, including apple, pear, quince trees, and various ornamental plants. The disease can destroy an entire orchard in a single growing season under ideal conditions, with the bacterium moving approximately 11 inches per week in new growth.
ð Symptoms
- âĒ Flowers and flower clusters appear water-soaked, then droop and shrivel, turning brown or black
- âĒ Blackened flowers and leaves remain attached to branches
- âĒ Young shoots wilt forming the characteristic shepherd's crook hook shape
- âĒ Leaves turn gray-green, then brown or black
- âĒ Sticky bacterial ooze on infected tissue
- âĒ Sunken, discolored cankers on branches and trunks
- âĒ Scorched appearance as if burned by fire
â Possible Causes
- â Erwinia amylovora bacterium that overwinters in cankers formed during the previous season
- â Spread by pollinating insects (especially bees) visiting bacterial ooze
- â Dispersal by rain splash and wind
- â Contaminated pruning tools transmit the disease between plants
- â Warm temperatures (70-80°F) and high humidity create ideal conditions
- â New, succulent growth is highly susceptible to infection
- â Excessive nitrogen fertilization promotes vulnerable growth
ð Treatment
Quick Fixes
Immediate Pruning
Cut all infected branches 8-12 inches below symptoms. Sterilize tools with alcohol between cuts. Destroy infected material.
Antibiotic Application
Spray kasugamycin or oxytetracycline within 24 hours. Acidify spray tank to pH 5. Apply thorough coverage.
Follow-up Sprays
Reapply antibiotic before predicted rain events. Continue every 3-5 days during warm, humid weather.
Organic Treatment
Sanitation Pruning
Remove all infected branches cutting 8-12 inches below visible symptoms. Sterilize tools between each cut with 70% alcohol. Burn or dispose of infected material away from garden.
Preventive Copper Application
Spray 0.5% Bordeaux mixture or soluble copper product on all affected and adjacent plants. Repeat every 4-5 days during wet periods.
Biological Control
Apply Blossom Protect (Aureobasidium pullulans) during bloom followed by Bacillus-based products after petal fall.
Continued Monitoring
Inspect plants weekly. Promptly remove any new infected tissue. Continue preventive sprays during disease-favorable conditions.
ðĄïļ Prevention
- â Plant resistant varieties when available (e.g., Kieffer, Moonglow, Orient pears; Enterprise, Freedom, Liberty apples)
- â Avoid excessive nitrogen fertilization, especially late in the season
- â Avoid heavy pruning in early summer that stimulates succulent growth
- â Reduce irrigation during bloom period
- â Maintain good air circulation through weed and cover crop management
- â Monitor regularly for early detection
- â Remove and destroy infected flowers and tissue as soon as detected
- â Sterilize pruning tools between cuts with 70% isopropyl alcohol or 10% bleach solution
ðą Care Guide: African Milk Tree
ð§ How to Water
Water only when soil is completely dry, typically every 3-4 weeks. Reduce watering in winter. Wrinkled leaves indicate thirst. Yellowing or browning may signal overwatering and root rot.
âïļ Lighting
Prefers bright indirect light to direct sunlight. Can tolerate some direct morning or afternoon sun. Avoid harsh midday sun which may cause scorching. Also adapts to medium light conditions.
ðŠī Ideal Soil
Use well-draining sandy or cactus mix. A 2:1:1 blend of cactus soil, perlite, and coarse sand works well. Good drainage is essential to prevent root rot.