Time for coffee and tea
A look at coffee tree disease
It is an interesting fact that Arabica is much more susceptible to diseases than the Robusta coffee tree; most of these diseases are a consequence of pathogenic fungi, though viruses and bacteria may also contribute. Though many of these diseases can be controlled by chemicals, they are still a limiting factor when growing Arabica coffee due to monetary factors. It is the aim of plant breeding programs to develop cultivars that are less susceptible to disease. The diseases that can impact coffee trees can be split into four main categories; those that affect beans; foliage; branches; and roots.
One of the biggest problems that affect coffee beans and berries is ‘coffee berry disease’, this is caused by the fungi Colletotrichum coffeanum, and has been known since the 1920’s when it was discovered in Kenya ; it has spread to most African coffee producing countries. Berries are most susceptible to infection by Colletotrichum coffeanum when they are expanding and when they are ripe. The disease can normally be controlled by copper based fungicides and captafol. Plant breeding effects have been directed at combating coffee berry disease, and resistant cultivars are grown in Kenya . Other fungi that are known to attack coffee beans and berries include Cercospora coffeicola and Botrytis cinerea.
Root diseases often affect coffee plants that are grown in areas of forest that have been reclaimed. Theses root diseases include Armillaria and Rosellinia species, both of which thrive on decaying stumps and roots of decaying forest trees.
The three main forms of coffee branch disease that are caused by Fusarium stilbodes are scaly bark (results in a thickening of the main stem and primary branch that leads to newly produced shoot death); Storey’s bark (leads to the death of suckers) and Collar rot (constricts the stem at the ground and leads to the death of the coffee tree). There are numerous other diseases that affect coffee stem and branch growth; these include attacks from fungi such as Pellicularia koleroga, Ceratocystis fimbriata, Rhizoctonia, Fusarium and Pithium.
Leaf rust is a major problem that affects coffee Arabica, indeed in countries such as Indonesia the rust resistant Robusta coffee tree is grown. Infection by Hemileia vastatrix occurs in the rainy season as infection of coffee trees by it can only take place in the presence of water. Although coffee leaf rust can be controlled by copper fungicide sprays it is best controlled by planting coffee leaf rust resistant cultivars.