Bioguide #15

Powdery Mildew Treatment: Karbyon

Using potassium bicarbonate for safe, organic powdery mildew treatment.

Powdery mildew is a fungal disease that affects a wide range of plant crops. The disease covers leaves in a white and/or blue coloured fungal growth that reduces photosynthesis and yield and leads to crop losses and reduced quality.

Powdery mildew infections are triggered by warm, wet weather with fungal growth covering a leaf within one week after infection. The earlier powdery mildew infects a crop, the more severe its effect on yield.

In forage crops, yield can be substantially reduced. For example, in forage kale, powdery mildew can reduce yield potential by 4 T DM/ha, potentially requiring farmers to buy in extra feed to cover the loss.

Powdery mildew is caused by a range of fungus which differs from crop to crop (see table 1). Note that some cultivars for crops are more resistant to powdery mildew.

Table 1: powdery mildew species that cause disease in different crops

Plant Powdery mildew causal agent
Grape Uncinula necator (Schwein.) Burrill 1892
Courgette Erysiphe cichoracearum DC. 1805
Cucumber Sphaerotheca fuliginea (Schltdl.) Pollacci 1913
Beetroot, silverbeet Erysiphe polygoni, E. betea
Swede, kale, turnip Erysiphe polygoni, E. cruciferarum
Capsicum Leveillula taurica (Lév.) G. Arnaud 1921

Potassium bicarbonate as a powdery mildew treatment

Potassium bicarbonate is a well-known powdery mildew treatment agent. When potassium bicarbonate is applied to an infected plant surface, it suppresses existing powdery mildew fungal growth. When applied prior to infection, it can provide even more effective control.

Potassium bicarbonate foliar sprays inhibit fungal spore germination and germ-tube elongation, as well as reducing spore formation for up to 7 days. This is due to multiple antifungal effects of potassium bicarbonate salts, including:

  • PH elevation on the leaf surface
  • The collapse of fungal cell walls due to a potassium imbalance
  • Dehydration of fungal spores.

These multiple modes of action of potassium bicarbonate lower the risk of pathogen resistance development when compared to synthetic chemical fungicides.

BioStart Karbyon

BioStart Karbyon is a fungicide spray for powdery mildew treatment – acting as both a direct treatment for infections and a preventative measure. The active ingredient in Karbyon is micro-encapsulated potassium bicarbonate, with the encapsulation improving the spread of Karbyon across the leaf.

BioStart Karbyon is an ACVM-registered (P8557) and BioGro Certified (4436) product for use as a powdery mildew treatment agent across a range of crops including:

  • Grapes
  • Berries
  • Vegetables
  • Cereals
  • Forage
  • Brassicas
  • Kale
  • Turnip
  • Swede
  • Fodder
  • Beet
  • Citrus
  • Ornamentals.

Sooty Mould in Citrus

BioStart Karbyon can also be used to treat sooty mould in citrus. Figure 2 shows the effect of two applications of Karbyon (1% solution – 10 days apart) on the leaves of an orange tree heavily infected with sooty mould. The two applications of Karbyon have removed the majority of sooty mould from the leaves. Similar effects have been observed in a number of commercial citrus orchards.

Figure 2. The effect of Karbyon on a heavy infection of sooty mould on an orange tree.

The panel on the left is the untreated control, whereas the leaves in the right panel have been treated with Karbyon applied at 1% (two applications, 10 days apart). The top row is before treatment, the bottom row is after treatment.

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