African Milk Tree with Canker? Rare but Treatable
Euphorbia trigona
Canker is a disease caused by various fungi and bacteria that create necrotic, sunken areas on bark of branches, stems, and trunks. Pathogens enter through wounds and natural openings, especially when plants are stressed. Canker can gradually weaken or kill branches by disrupting water and nutrient flow.
ð Symptoms
- âĒ Sunken, discolored lesions on bark
- âĒ Oval to elongate dark areas on stems and branches
- âĒ Bark splitting and cracking
- âĒ Sap or resin oozing from infected areas
- âĒ Blackened inner bark tissue
- âĒ Progressive branch dieback beyond lesion
- âĒ Wilting foliage above infection site
- âĒ Small raised fruiting bodies on bark surface
- âĒ Complete girdling of stems and branches
- âĒ Yellowed, curled, or sparse foliage
â Possible Causes
- â Fungal infection by Cytospora, Phomopsis, Nectria, and Botryosphaeria genera
- â Bacterial infection by Pseudomonas syringae
- â Pathogen entry through pruning wounds, mechanical damage, or insect injuries
- â Plant stress from drought, transplanting, or winter damage
- â Extreme temperatures and adverse environmental conditions
- â Improper cultural practices weakening the plant
- â Bark wounds serving as entry points for pathogens
- â Poor species selection for local conditions
ð Treatment
Quick Fixes
Identify and mark all branches with canker
Use colored tape to mark affected areas
Prune infected branches 6-8 inches below lesion
Use sterilized tools; do on dry day
Immediately apply copper fungicide to wounds
Copper-based products are most effective
Dispose of all infected material in sealed trash
Do not leave on ground or compost
Spray systemic fungicide on entire plant
Thiophanate-methyl or propiconazole
Second systemic fungicide application
Follow label instructions
Inspect for new symptoms
Prune immediately if finding new cankers
Final evaluation and preventive application
Continue monthly monitoring
Organic Treatment
Carefully inspect entire plant identifying all cankers
Use flashlight to examine bark for sunken lesions
Prepare clean pruning tools and 70% alcohol for sterilization
Sharp pruning shears and saw for larger branches
Prune all infected branches 6-8 inches below visible lesion
Do on dry day; sterilize between cuts
Apply bordeaux paste to pruning wounds
Protects against reinfection
Dispose of infected material in sealed trash
Do not compost diseased material
Spray neem oil on entire plant
Apply in late afternoon; repeat every 14 days
Apply compost tea to soil around plant
Strengthens immune system
Second neem oil application
Continue biweekly for 2 months
Inspect for new cankers and prune if necessary
Monitor especially areas near old lesions
Evaluate overall health and adjust irrigation and fertilization
Reduce stress to prevent recurrence
Final inspection and preventive bordeaux mixture application
Apply before rainy periods
Continuously monitor and maintain proper cultural practices
Prevention is the best strategy
ðĄïļ Prevention
- â Maintain plant vigor through proper planting, watering, and fertilization
- â Select species and varieties adapted to local soil and climate conditions
- â Avoid all unnecessary bark wounds
- â Prune only when necessary and in dry conditions
- â Sterilize pruning tools between each cut with 70% alcohol or bleach solution
- â Apply mulch to maintain soil moisture and reduce stress
- â Protect plants against winter damage and frost
- â Remove dead or diseased branches promptly
- â Avoid pruning when bark is wet to reduce spread
- â Regularly inspect plants for early detection
- â Minimize water stress through adequate irrigation during dry periods
- â Apply balanced fertilizers to maintain overall plant health
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.