Stemming tree cankers with cuprous oxide fungicide

Cleaned stem canker wounds on cocoa are protected and sealed by applying cuprous oxide canker paint (Source: Nordox)

Like all copper-containing fungicides, cuprous oxide is active against a broad range of fungi and bacteria and is therefore able to deal with most secondary invaders as well as the primary Phytophthora pathogen. Cuprous oxide is acknowledged to be the most efficacious of all fixed copper fungicides (on a gram to gram basis), and its rich dark red colour means estate managers can easily see whether or not a tree has been treated.

Cuprous oxide is inherently tenacious. Use of oil emulsions or adjuvant sticker to formulate paints will further increase tenacity and resistance to weathering. That said, canker paint protection is a long term business lasting months if not years and clearly requires a waterproof covering layer of thick petrolatum grease or other equivalent sealant known to encourage bark renewal.

Paint should ideally be dry before applying sealant but this may not be possible in the wet and humid tropics. Sealant should cover the entire cleaned and painted area and at least 5 cm beyond the edge of the treated area. Treated areas should be inspected over the following months for bark renewal, and the paint and/or sealant re-applied if necessary.

South East Asia is where most innovative work with canker cleaning, painting and sealing takes place. Farmers add polymer materials to the paint to obtain a ‘two-in-one’ canker paint/wound sealant that provides a self-sealing impenetrable crust over the treated area. Sealing of the painted area is not only for waterproofing and prevention of re-infection, but to deter bark and wood boring insect pests like beetles which are attracted to damaged areas of bark and exposed wood.