Growers Section Common Pests & Diseases
Common Pests & Diseases
Anthracnose fungal disease
Some growers have reported the incidence of anthracnose on their fruit. Anthracnose is a fungal disease which causes a blemish on the skin of the fruit, as this blemish spreads the flesh below goes brown and rots. Eventually the olive is destroyed and will either hang in the tree or fall to the ground when the branch is disturbed.This condition is very serious because the fruit is unsuitable for any type of processing. Occurrence of anthracnose requires preventive treatments of copperoxychloride (Copper Spray) during fruit development, this has helped reduce it's severity.
The onset of prolonged rain in early Feb/March gives the fungus the ideal conditions to spread. Fruit higher in and towards the centre of the tree appears to be worst affected. This is possibly due to the methods of spraying and the spray penetration into the centre sections of the tree being hampered by foliage. This combined witht the fruit being more protected from sunlight and likely to stay wetter longer periods in this area of the tree.
Affected fruit will drop from the tree and create a bed of anthracnose spores under the tree ready to be swept up onto the leaves by prevailing winds over the coming months ensuring a continuation of the problem the following year. Ideally fallen fruit should be removed from the grove floor to reduce the problem however in reality this would prove at best difficult to achieve.
To reduce the amount of anthracnose affected fruit first of all requires trees to be pruned in a way that allows free air movement and therefore adequate spray penetration. This will also aid in the reduction of damp humid conditions and also hasten the drying of fruit in all sections of the trees. Secondly the condition can be controlled to some extent by the use of copper based he sprayed onto the foliage in July to mid August prior to flowering, again after fruit set in mid September/October with follow-up spraying ithroughtout the fruiting stages up until harvest. All spraying must be done in accordance with the spray rates and withholding guides supplied by the manufacturer of your chosen copper based fungicide.
Weather conditions on the North Coast may indicate that a spraying regime is required to ensure that anthracnose doesn't cause a major loss of income due to crop loss and rejection of affected by the processor.
Recent observations have also connected the problem to a pest known as the Green Vetetable Bug. Control of this new pest will limit surface damage of the fruit and combined with a above measures will recduce the severity of anthracnose.
Olive Lace Bug
A lesser worry to established trees, but can be a major problem in young trees. The Olive Lace Bug (OLB) lives on the underside of leaves out of direct sunlight. It feeds on leaves, sucking them dry, if present in large enough numbers the OLB will defoilate a young tree and kill it. In any case the OLB will cause stress in the olive, reduce it's photosynthsis through damaged leaves & loss of leaves resulting in lower growth potential. Affected trees have visible yellowing leaves and considerable leaf drop. OLB lays eggs on the leaves, which in turn fall to the ground where the life cycle of the OLB continues relatively unaffected by foliar sprays. When OLB eggs hatch and progress through to flying adults they move back into the tree foilage to continue damaging the foilage. OLB numbers build and spread from these hotspots within the grove.
There is no known natural preditor of the OLB. Prevention of building up large populations of OLB is the key to control. Spraying with organic sprays has limited success as the product has to strike the OLB to be affective and as OLB shelters on the underside of the leaf this is difficult to acheive. Application of Dimethoate [AOA to sept 09] (Check for up-dated off label permit before use) to the foilage has more success as the chemical is a systemic and is absorbed into the trees system and delivered the the OLB as it feeds. Spray timing is also critical to arrest the breeding and reinfestation of the trees and also to limit the spread of the pest within the grove.