Alternaria leaf spot of the cabbage family
Round brown to black spots with rings like a target and a yellow halo appear on older leaves, and heads may show dark specks.
Crops it strikes
What you see
When to act
Check the outer leaves every week from transplanting. Start protectant sprays when brown target spots show on the lower leaves in wet weather, and keep spots off the heads and the seed pods in the weeks before harvest.
What to spray
- MancozebFRAC M03ShopeeLazada
- Azoxystrobin plus difenoconazoleFRAC 11 plus 3ShopeeLazada
- DifenoconazoleFRAC 3ShopeeLazada
- ChlorothalonilFRAC M05ShopeeLazada
- Difenoconazole plus pydiflumetofenFRAC 3 plus 7ShopeeLazada
- Tebuconazole plus trifloxystrobinFRAC 3 plus 11ShopeeLazada
- Fluopyram plus trifloxystrobinFRAC 7 plus 11ShopeeLazada
- Bacillus amyloliquefaciensFRAC BM02ShopeeLazada
- Propineb plus trifloxystrobinFRAC M03 plus 11ShopeeLazada
- TebuconazoleFRAC 3ShopeeLazada
- Copper hydroxideFRAC M01ShopeeLazada
- Bordeaux mixtureFRAC M01ShopeeLazada
Active ingredients only, never brands. The FRAC group tells how it works: switch to a different group next time, so the disease does not learn to survive it. Spray only when the damage is worth the cost, and only with products registered with the Fertilizer and Pesticide Authority for your crop. Follow the label. The Shopee and Lazada links only show who sells something with that active ingredient, not a recommendation of any seller or product.
On labels for it, but not advised
- Benomyl: Alternaria fungi are hardly touched by benomyl and its kin. Use mancozeb or a triazole for this leaf spot.
- Thiophanate methyl: Alternaria fungi are hardly touched by this group. Use mancozeb or a triazole for this leaf spot.
How to prevent it
- Sow clean seed. Soak doubtful seed in hot water at 50 degrees Celsius for 25 minutes before sowing.
- Rotate for three years away from the cabbage family, and pull mustard family weeds near the field.
- Plow under or remove crop residue right after harvest.
- Space plants so the leaves dry quickly, and water at the base in the morning.
- Feed the crop evenly with enough potash. Stressed and old leaves spot first.
Natural enemies and biological help
- Bacillus based biofungicides help as protectants when sprayed before spots spread.
Where this comes from
Not sure it is this one?
Many diseases look alike. Send a photo to Anee, the smart farm technician in anee.io. She reads it with your crop, its age and the weather, and tells you what it most likely is and what to do first. In Tagalog or English.