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Coffee cultivation: The biological threats

The threat to coffee crops from biological problems – such as fungus, insects, bacteria and mould – are numerous, with leaf rust currently having a notable adverse effect on yields around the world.

It is important to understand the issues that can damage or kill coffee plants in order to protect crops and ensure the best possible beans are produced.

In fact, a new coffee pest has been discovered in Hawaii this year by Dr Scot Nelson and Dr Michael Melzer, and the experts are now seeking the help of coffee farmers and members of the community to provide them with more information about the virus.

Symptoms of the disease include circular yellow or yellow-green lesions on leaves and stems of coffee plants, and it is thought to damage coffee cherries.

Leaf rust epidemic

When it comes to biological threats to coffee plants, first and foremost in the minds of many working in the trade of green coffee is leaf rust, which has reached epidemic proportions in some coffee-growing regions of the world.

Leaf rust is a fungus that is also known as coffee rust and has been a problem since the 19th century. Now found in most coffee-growing nations, it is dispersed by wind and rain, and causes orange-coloured lesions to appear on the leaves of coffee plants and spread, leading to defoliation. The spores weaken the tree and reduce yields.

Last year, almost three-quarters of the coffee crop in El Salvador was affected by leaf rust, while the International Coffee Organization reports that the current epidemic has affected 53 per cent of countries in Central America – the worst outbreak of the disease in the region since 1976.

Some nations declared a phytosanitary emergency and crisis summits were held by coffee specialists, with measures in place to combat the problem including using pesticides, coffee plant renovation programmes to introduce more resistant varieties and climate change adaptation.

Insect pests that threaten coffee crops

However, in addition to the threats that cannot be seen with the naked eye, there are insects that can threaten coffee crops. One of the most damaging of these is the coffee borer beetle. The small black insect tunnels into coffee fruit, laying eggs and potentially destroying the entire crop in a region, if it manages to spread unchecked.

In addition, the black twig borer beetle, native to Asia, attacks both Robusta and Arabica coffee. The females burrow into plants, destroying them through tunnelling and the release of pathogens.

Also found in Asia, the larvae of the coffee white stem borer tunnel into the stems of plants and affect their stability, thereby reducing yields.

Ways of combating infestations of these beetles include pruning, shade reduction and ensuring that all coffee is harvested with each crop.

Other insects that can damage coffee crops are cicadas, the larvae of the coffee leaf miner moth, grasshoppers, green scale, the soldier fly and spider mites, such as the coffee red mite and the southern red mite.

Damp and humid conditions can fuel biological damage

A lot of the pests that threaten coffee crops – such as the coffee borer beetle – thrive in humid conditions, as do many of the fungi and moulds that can attack plants.

For instance, yeast and mould growth can damage the appearance and taste of beans both as they are growing and when they are being stored.

Similarly, climate change has been identified as posing a threat to coffee crops in a range of ways, from the severe drought that is harming yields in Brazil at the moment, to increases in the hot and humid temperatures that can cause many biological diseases and pests to thrive.

Action can protect crops from biological threats

Epidemics decimate crops and push up global coffee prices, so it is important that coffee farmers employ measures that reduce the risk of biological problems and safeguard their plants.

Farmers must remain vigilant to not only insects and fungus, but also other biological problems that affect many plant crops, such as weeds, phoma, nematodes, parasites, rot, blight, canker and leaf spot.

Furthermore, larger animals sometimes cause damage to coffee plantations, with pests of this kind like rats, mice, birds, bats and even pigs, monkeys or wild boar potentially wrecking coffee trees.

Depending on the pest or threat being faced, actions that can reduce the risk to yields and ensure the unique quality and flavour of a crop is preserved may include installing barriers (to prevent wind-borne spores from reaching plants or to keep out large animals), effective pruning, pesticides, fungicides, insectivorous birds and checking plants being moved carefully for pests.