Australia is fortunate to be free of the two most serious and widespread coffee diseases, coffee berry disease and coffee rust. Coffee trees in Australia have only a few pest and disease problems and these are not serious.
Green coffee scale ( Coccus viridis) and mealy bug (Planococcus spp.) are the two most common pests. Both attach themselves to leaves and young branches and draw nutrients from the tree. In large numbers they cause a general decline in tree health, affecting yield. Ants are often associated with scale and mealy hug attacks, because they farm the insects. They spread the scale and mealy bug around the tree and from tree to tree, and loosen the soil at the base of trees, making them prone to lodging.
Sooty mould grows on the sticky residues produced by the scale and mealy bugs and covers the leaves, reducing photosynthesis and contributing towards a decline in tree health. In warm dry environments scale and mealy bug can become widespread and you may need to control them chemically.
White oil, refined water-miscible oil and Lorsban® (200 m1/100L, plus wetter 1%, in Queensland only) have been used successfully.
Research trials have shown that where there are only minor infestations, natural predators (parasitic wasps) and diseases ( Verticillium) usually keep populations under control. In these situations avoid spraying chemicals so that natural predator populations can increase. Verticillium fungus is most active in warm moist conditions.
Preliminary entomological studies show that a naturally occurring insect hormone called methoprene may be useful for controlling ant populations in the future and hence the occurrence and spread of scale and mealy bug.
Other insect pests which cause minor problems are cicadas and their larvae, and scarab beetles which attack the roots of coffee trees. These can usually be controlled by cultivation before planting. In established plantations with closed canopies these insects are not usually a problem.
The only significant disease in coffee trees is cercospora (Cercospora coffeicola), fungus which causes leaf spotting and defoliation (see Plate 3:5). It is most prevalent in warm wet weather, in nurseries and during early field establishment.
It is nearly always associated with trees in poor health, especially trees with nutrient deficiencies. The best control is by correcting the nutrient deficiencies. In bad attacks repeat sprays of foliar copper (copper oxychloride 4 g/L) will control the fungus.
James Drinnan and Ted Winston