Black Spot Management In Kales

Black spot disease is one of the most significant diseases in kales. The disease, caused by a fungus (Alternaria brassicae), can cause serious losses in kales. Moderate infections could cause up to 10% losses. The pathogen may be seed-borne and may as well survive when buried in the soil as resting spores.

Black spots can cause kales consumer rejection, the spots also provide route for other infections/diseases. The disease slows down plant growth by making it weak. The infected leaves sometimes dry up and falls off the plant reducing surface for photosynthesis.

The disease slows down plant growth by making it weak.

Disease Description

The disease-causing pathogen thrives best in moist and warm conditions. The spores multiply rapidly when its moist i.e. during long rains, excessive irrigation and heavy dew during night hours.
The spores are either spread by wind, equipment used in the farm, splashing water and movement of workers within the farm/outside. The spores have ability to travel up to 1.5 kilometers by wind.
Under its favorable conditions (moist and warm)- the fungus germinates/multiplies as soon as it lands on the plant’s leaf surface. Once it establishes, it penetrates the kale leaves using infection pegs (special structures used by fungi to attach themselves on their hosts) takes hold and begin to spread on the leaf surface of the kale. The disease affects kales throughout the crop production cycle (seedling to harvesting)


Early Detection of Black Spots in Kales

The first symptoms of blackspot infection are formation of yellow, brown to dark small spots on the leaves. In warm and wet conditions, the spots rapidly enlarge as more spores develop.

Cultural Practises To Prevent

  • Proper weed control to allow for free flow of air of kales to avoid high levels of moisture around the crops. This also eliminates other potential hosts among the weeds.
  • Irrigate during morning hours to reduce duration of leaf wetness
  • Mulch your kales immediately after transplanting with organic materials to prevent splashing of water that spreads soil borne Alterania brasicca pathogen
  • Proper crop spacing for good air circulation in the seedbed
  • Seedlings should not be crowded in the nursery
  • Regular monitoring/scouting to arrest the disease early enough
  • Purchase disease-free seeds these will help you overcome seed-borne Alternaria Brassica pathogen
  • Don’t work on plants when its wet to avoid transmitting the pathogens
  • Crop rotation that is the location/ portion should go for 2-3 years without brassica family and squash family

Organic Solutions

  • Use neem oil which creates an inhospitable environment for pest that might carry the pathogen. Mix two tablespoons of neem oil and 1 tablespoon of regular liquid soap/liquified bar soap with 2-3litres of water for the application. Use a knapsack or hand sprayer to spray the solution. Ensure that the whole leaf surface is covered- including the underside of the leaf.  

Use bio fungicides such as:

  • Serenade garden (Bacillus subtilis)
  • Double nickel (Bacillus amyloliquefaciens)

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