Anthracnose

Anthracnose is a dreaded word for most of us, because we don’t know what it is, and we don’t know how to deal with it.

What makes it worse is that it can affect nearly all types of plants. It’s most noticeable here in Hawaii on papayas, mangoes, and plumeria trees.

Anthracnose is a fungal disease caused by various species of the genus Colletotrichum, and it can be easily identified by the telltale black spots on leaves and fruit. The lesions on fruit can become sunken when the disease has progressed, and while cutting away the affected areas of the fruit leaves the rest edible, the appearance of the fruit is rather off-putting.

This is commonly what is seen when a mango tree is infected with anthracnose. Black spots and lesions can also appear on the leaves of the tree.

This is a fairly mild anthracnose infection on papaya fruit. The leaves of a papaya are generally infected prior to fruit, and can be easily identified.

On plumeria, the disease shows primarily on the leaves and does not affect the flowers.

Treatment of anthracnose generally involves a topical antifungal treatment, though sometimes with severe infections, a systemic injection or even root bath may be recommended.

Because of the ease with which the disease spreads, collecting and disposing of infested material is imperative. Please do not dump infected greenwaste in common areas - bag it, seal the bag and put it in the rubbish. Or better, burn it.

Antifungal treatments range in toxicity - I will generally recommend avoiding anything toxic on food plants, because no matter what “they” say, I can’t avoid believing that the toxic elements will end up in the food that’s being produced.

One of the most common antifungal treatments is a topical copper sulfate application, generally sprayed on. It is important to use a separate sprayer container for different types of applications! A popular trick to increase the efficacy of copper sulfate as an antifungal is to make a Bordeaux Mix, but it is extremely important to follow instructions carefully when making this powerful mixture.

Copper sulfate is generally considered safe for use on food plants as it would take an extreme volume to cause toxicity in a person. However, overuse can cause toxicity in the soil at a level that damages earthworms and soil microbes.

Early detection, proper drainage, and limiting damp, still environments are better than resorting to topical treatment. Cutting back affected parts of the plant and working to prevent infestation are also key.