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Symptoms A black soot-like growth which can cover all surfaces of the plant. Severe infections can indirectly cause plant stunting and unthriftiness, as the soot coverage prevents sunlight penetration and thus photosynthesis by the plant.
Control To manage sooty mould, the insects producing the honeydew must be controlled.
52 Stem death Symptoms The stem of the plant dies a few centimetres above ground level. The base is generally healthy and new shoots will appear below the dead stem. Most common on young trees in their ﬁrst and second years in the ﬁeld.
Cause Unknown. Damage occurs to the young tree and allows entry of wound-invading bacteria and fungi (see Wound Cankers, p 48). Damage is often associated with cold temperatures, sun scald and herbicide, but in many cases the cause has not been determined.
L: Sun scald on young olive tree Middle & R: Stem death on young olive tree
© NSW DPI © SARDI
53 Tip death Symptoms Ends of branches die for no apparent reason.
Tip death appears to have no effect on the general health of the tree or its productivity. Branches can be removed if this is considered necessary for cosmetic purposes.
Inspection of the stem below the dead tips is needed to determine whether the death has a speciﬁc cause which should be further investigated (see Wound Cankers, p 48). Root rot and trunk cankers can also cause tip death, and so should be investigated.
© SARDI © SARDI
54 Miscellaneous leaf damage There are many other symptoms seen on leaves that have no known cause. They may result from infection by biotic agents or from environmental or nutritional effects. Symptoms include white spotting, pale brown blotches, striping and yellowing, and dead tips.
55 Key olive pests & diseases not detected in Australia There are many pests and diseases both of olives and other crops overseas that are potential threats to the olive industry. For example, Phytophthora ramorum, the cause of sudden oak death in California and Europe, can cause disease in some olive cultivars.
The following pests and diseases are of more immediate concern to the Australian olive industry.
Phytoplasmas Phytoplasmas are small infectious agents usually spread by leaf hoppers. Symptoms include bushy growth, witch’s broom, chlorosis and deformation of leaves, ﬂower abortion, bud failure, and formation of sphaeroblasts (p 52) with rosettes of shoots.
56 Viruses and virus-like diseases At least 14 different viruses and several virus-like diseases are known to occur in olives overseas, and some have been detected in symptomless trees. While many viruses have been recovered from affected trees, there is often no proof that the virus causes the symptoms observed. They can be transmitted by soil-borne vectors such as nematodes, and by aphids and pollen. These viruses may already be present in Australia but remain undetected. All imported olives are currently tested for viruses.
Symptoms include deformed fruit, poor fruit set, reduced yield, leaf distortion, narrow twisted leaves, bushy growth, small leaves, bright yellow discoloration of leaves, chlorotic to yellow vein discoloration, defoliation and dieback.
The main viruses detected are Strawberry Latent Ringspot Virus, Olive Latent Ringspot Virus, Arabis Mosaic Virus, Cherry Leafroll Virus and Olive Latent Viruses 1 and 2.
Martinelli GP, Salerno M, Savino V, Prota U (2002).
An appraisal of diseases and pathogens of olive, in ‘Proceedings of the 4th International Symposium on Olive Growing’, Acta Horticulturae 586: 701–8.
Olive ﬂy, Bactrocera oleae (Diptera:
Tephritidae) Size 5 mm long Biology and damage Olive ﬂy is the most important pest of olives worldwide. It is endemic to the Mediterranean and is established in Mexico and California.
The female lays eggs in fruit, and developing larvae (maggots) feed on the olives, usually causing fruit drop. Mature larvae may pupate in the fruit or leave and pupate in the soil, where they overwinter. Fruit rot and lower oil quality are associated with damage.
In the USA, olive fruit is required to be 1% infested for processing. If uncontrolled, olive ﬂy can result in 100% loss of the table olive crop and 80% loss of the oil crop. It appears that olive ﬂy has a preference for some cultivars, particularly large-fruited ones.
Olive ﬂy adult on olive leaf 58 Olive ﬂy is related to, and looks similar to, the Queensland fruit ﬂy (p 25), but is smaller, has dark marks on its wing tips and has slightly different markings. It is attracted to a speciﬁc pheromone (communication chemical) that is different from those of both QFF and medﬂy, which is used to monitor it and as part of a control strategy. Control is difﬁcult and costly.
Damage caused to olives by olive fruit ﬂy larvae (below), and larva in fruit (bottom).
59 Olive moth, Prays oleae (Lepidoptera: Yponomeutidae) Size Adult moth 6 mm long, 13 mm wingspan Biology and damage Olive moth is widespread in Mediterranean countries and also occurs in Central and South America. The only host is olive. Adult moths are silvery grey, and have long antennae.
There are normally 3 generations per season. The ﬁrst generation arises from eggs laid by overwintered adults on ﬂower buds and ﬂowers. Emerging caterpillars feed on pollen, anthers and female parts of ﬂowers.
Caterpillars of the second generation burrow into fruit and feed near the kernel, causing severe fruit damage and fruit drop. Those of the third generation feed on leaves. Reported crop losses are variable.
Control is achieved most commonly by pesticides. Pest presence (but not population size) is monitored by using a synthetic pheromone (sex attractant for male moths), or light or food traps. Pheromones are also being evaluated to manage olive moth by disrupting mating.
© Int. Olive Council Olive moth larva 60 Diseases present in Australia but not yet detected on olives Some diseases present in Australia on other crops have been reported as diseases of olives overseas, but have not yet been detected on olives in Australia.
Armillaria root rot Cause Fungal: Armillaria spp.
Causes gradual decline and death. White to yellow fanshaped mycelial mats are observed between the bark and wood.
Black root rot Cause Fungal: Thielaviopsis basicola Causes foot and root rot of mature olives, leading to tree decline.
Cause Phytophthora fruit rot Water mould: Phytophthora spp.
Causes fruit rots, particularly in wet weather.
61 Glossary Abiotic—Caused by non-living factors.
Beneﬁcial organism—An organism that helps the crop.
Biological control—The use of living organisms to control pests or diseases.
Canker—Dead or diseased area on a branch or stem.
Crawler—The juvenile stage of scale insects.
Defoliation—Loss of all leaves from a branch or tree.
Disease—Any adverse effect on plant growth and development. In this book we have used ‘disease’ to describe damage caused only by pathogens.
Disorder—Any adverse effect on plant growth and development from an abiotic cause.
Gall—An abnormal growth of plant tissue from proliferation of cell division, similar to callus tissue.
Honeydew—A sugary solution excreted by many sapsucking insects.
Integrated pest and disease management—The combination of several strategies to control pests and diseases for maximum results with minimum drawbacks (p 9).
Larva—The juvenile stage of an insect; commonly used for caterpillars and grubs.
Lenticels—Natural pores or breathing holes in the outer layer of plant tissue.
62 Nymph—The juvenile stage of an insect in which the juvenile and adult look very similar.
Opportunistic—Making use of an opportunity that presents itself, rather than looking for a goal. Often used to describe an organism that infects plant material through wounds or damage inﬂicted by another cause, either abiotic or biotic.
Oviposition—The laying (positioning) of an egg (ovum).
Parasite—An organism that derives its nourishment from another organism without killing it.
Parasitoid—An organism that derives its nourishment from another organism and eventually kills it.
Pathogen—Any organism that causes disease, e.g.
bacterium, fungus, virus.
Predator—An organism that catches others for food.
Pupa—The case-like intermediate stage of many insects between larva and adult, in which the insect develops.
Sclerotia—Small black resting bodies of a fungus which enable it to survive without the plant host.
63 Further reading These books provide additional information on olive diseases (1, 2, 3) and insect pests and beneﬁcial insects (4, 5). Books 1 and 2 are available through the Australian Olive Association. There are also many websites that provide good information on olive production and olive pests and diseases.
1. Olive Pest and Disease Management (1999). LopezVillalta MC. Available from the IOOC, Madrid, Spain.
2. Olive Production Manual, 2nd edn (2005). Sibbert GSU & Ferguson L. University of California.
Available from ANR (University of California).
3. Olive Growing in Australia: A Comprehensive Guide (in press 2007). Sweeney S, ed. Available 2008 from Rural Solutions, SA, and Lenswood and Loxton PIRSA ofﬁces, SA.
4. Citrus Pests and Their Natural Enemies (1997).
Smith D, Beattie GAC, Broadley R, eds. Available from DPI Publications, Queensland.
5. The Good Bug Book, 2nd edn (2002). Llewellyn R et al. Available from Integrated Pest Management Pty Ltd, Queensland, and from Australasian Biological Control Inc., NSW.
tar spots 30 Theba pisana 34 Thielaviopsis basicola 61 thrips 13, 35 Thrips imaginis 35 tip death 54 Trichogramma carverae 68