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Ways of controlling weed on trees

Lichen growth is most prevalent on the adaxial (upper) surface of leaves such as coffee, citrus and avocado, which possess a natural thick waxy cuticle. (Image source: Terry Mabbet)

Epiphytes 5

Epiphytes promote and encourage disease

Phytophthora pathogens (called ‘water fungi’ by early mycologists) are dependent on high humidity and surface wetness for spore production, spore dissemination and infection of pods and flower cushions, the latter borne directly on the branches of the cocoa tree. Prolific and dense epiphytic growth comprising mosses, ferns and bromeliads, encourages and aggravates the development and spread of Phytophthora in cocoa.

This in turn will cause higher than normal levels of pod rot and stem canker, the latter developing from infected flower cushions. In many parts of the world Phytophthora pod rot is so severe that farmers are unable to harvest any pods unless trees are sprayed weekly with copper fungicide, at least during the rainy season. Another way in which epiphytic growth encourages and promotes disease in cocoa is by trapping Phytophthora spores which subsequently germinate and infect flower cushions and cocoa pods. 

Stem cankers develop quickly and girdle the branch or trunk to kill the tree which otherwise has a crop bearing life of at least fifty years. This general disease increase is due to creation of high relative humidity, but epiphytes growing on the trunk and branches of cocoa trees may cause specific damage related to flowering and the formation and development of minute young pods called ‘cherelles’.

Cherelles are prone to substantial losses from a condition known as ‘cherelle wilt’. This may be purely physiological, caused directly by Phytophthora pathogens infecting flower cushions (Phytophthora cherelle wilt) or a combination of both. In addition, the growth of moss may be so rapid, extensive and dense that it physically smothers the flowers and cherelles on the flower cushions. 

Cauliflorous flowers particularly at risk

Cocoa flowers grow from small cushions on the trunk or older branches of the tree. Botanists are notorious for inventing all sorts of terms to explain different floral phenomena. Flowers borne directly on the trunk, limbs and main branches of woody plants rather than on new growth is called ‘cauliflory’.

This term is derived from the Latin and literally translates into ‘stem + flower’.  The cocoa flowers are said to be ‘cauliflorous’. Cauliflory is not particularly common amongst the trees of the world. Other tropical trees showing this type of flower and inflorescence bearing include jackfruit (Artocarpus heterophyllus), breadfruit (Artocarpus attilis), and papaya. The main advantage is allowing the pollination of flowers and the dispersal of fruits and seeds by animals which cannot fly.

One of the few non-tropical trees showing ‘cauliflory’ is Cercis siliquastrum, commonly known as the Judas tree, a small, deciduous and leguminous tree native to Southern Europe and Western Asia and noted for its prolific display of deep pink flowers in spring. A related species with closely matching pink cauliflorous flowers and native to eastern North America is the eastern redbud (Cercis canadensis). In the western United States including California, Arizona and Utah it is replaced by the western redbud (C. occidentalis).

More general damage to tree crops from long term heavy epiphytic growth is branch breakage caused by the extra ‘loading’ on the tree. This is especially common in citrus, whether orange, grapefruit, lime, mandarin or other species and cultivars.