«Robert Spooner-Hart, Len Tesoriero, Barbara Hall 1 © 2007 Rural Industries Research and Development Corporation. All rights reserved. ISBN 1 74151 ...»
L: Olive lace bug adult with 5 nymphal instars R: Mallada signata adult L: Green lacewing egg R: Mallada signata larva predating on lace bug nymphs
© Qld DPIF 31 Olive fruit caterpillar, Cryptoblabes sp. (Lepidoptera: Pyralidae) Size Adult 15 mm wingspan Biology and damage An unidentiﬁed species of Cryptoblabes has recently been recorded feeding on fruit in southern Queensland. The moth, which probably migrates from neighbouring cereal crops, lays eggs, which hatch into larvae that feed on the surface of fruit, producing webbing and frass (faeces).
Comments Unlikely to be a problem unless olives are located near cereal crops such as sorghum.
32 Rutherglen bug, Nysius vinitor (Hemiptera: Lygaeidae) Size Adult 5 mm Biology and damage Commonly breeds on weeds, especially developing seeds. Occasionally reaches plague numbers in spring and summer and may swarm onto trees. Heavy feeding can cause severe damage with scorched appearance of leaves and death of twigs.
Generally of minor importance, although may be prevalent in some districts in favourable seasons.
Comments Closely related species with similar habits include grey cluster bug Nysius clevelandensis, coon bug Oxycarenus arctatus, and cottonseed bug O. luctuosus.
Adult (L) and nymph (R)
© NSW DPI © NSW DPI
33 Snails (Mollusca: Gastropoda) Snails, including the small brown snail Microxeromagna vestita and the while Italian snail Theba pisana, are a problem in some areas of SA and WA. They appear to cause limited feeding damage, but they rest in trees, smothering trunks and branches, and occasionally causing broken limbs from their weight. In SA they move off trees in autumn and are not present during the critical harvest period, when they could contaminate the fruit.
White snails on olive tree
34 Thrips (Thysanoptera) Plague thrips, Thrips imaginis Western ﬂower thrips, Frankliniella occidentalis Size T. imaginis fem. 1.0–1.3 mm, male 0.8–1.0 mm F. occidentalis fem. 1.4–1.8 mm, male 0.9–1.1 mm Behaviour and damage Thrips are small, elongated insects. Adults range in colour from yellow to midbrown. Larvae are white or cream and wingless. Both species have been recorded in olive ﬂowers, but plague thrips is the more common in ﬂowers and on sticky traps in groves. Thrips commonly feed on understorey weed ﬂowers in the grove or in nearby ﬁelds, swarming between spring and autumn. Flower infestations have been implicated in scarred and misshapen fruit.
Natural enemies Predatory thrips and predatory mites (Acari: Phytoseiidae) may attack thrips larvae.
Comments Predatory mites (e.g. Eusius montdorensis) are being developed commercially for use in greenhouse crops against F. occidentalis. Field use is doubtful.
L: Plague thrips feeding on citrus ﬂower stamen R: Western ﬂower thrips
© NSW DPI © NSW DPI35 Weevils (Coleoptera: Curculionidae) Curculio beetle, apple weevil, Otiorhynchus cribricollis, in inland NSW, SA & WA Garden weevil, Phlyctinus callosus, mainly in WA Size Otiorhynchus cribricollis, 9 mm Phlyctinus callosus, 7 mm Biology and damage Adults are nocturnal and ﬂightless, and climb trees to chew leaf margins. Severe infestations can damage growing tips, especially in young trees. The soil-dwelling larvae (legless grubs) may damage tree roots.
Comments An effective alternative to insecticide application to butts of trees is the use of either a sticky or a ﬁbrous barrier applied to the tree trunk. In the latter case, garden weevils in particular become enmeshed in the ﬁbres.
Poultry such as guineafowl have been reported to contribute to garden weevil control in orchards and vineyards.
L: Weevil damage to olive leaves R: Adult Otiorhynchus cribricollis
37 Diseases Anthracnose Cause Fungus: Colletotrichum acutatum, C. gloeosporioides Symptoms Causes soft circular rots on the fruit, usually on the shoulder, and at high humidity produces an orange slimy mass of spores on the fruit surface.
Commonly seen close to harvest when fruit softens.
Transmission Survives on infected mummiﬁed fruit.
Spores are spread by rain splash and wind. Can infect ripe fruit and form new spores within 4 days.
Favoured by Wet conditions with high humidity.
38 Charcoal rot Cause Fungus: Macrophomina phaseolina (also called Rhizoctonia bataticola) Symptoms Plants die back from the shoots, and leaves drop. Infected roots appear grey and are dotted with tiny (pinhead-sized) black sclerotia, which are survival structures of the fungus. Severely affected roots blacken and rot away.
Transmission Soilborne. This fungus survives in soil for many years and can infect roots and stems of a wide range of plants. It spreads in irrigation water and infected soil on farm machinery.
Favoured by Warm and dry soils. Leaf symptoms develop when plants are heat stressed.
© NSW DPI
39 Crown gall Cause Bacterium: Agrobacterium tumefaciens Symptoms Forms swellings and galls on stems and roots near soil level. Galls start as small, pale lumps of tissue, which enlarge, darken and become convoluted. Galls can vary considerably in size. Can be confused with olive knot galls (p 43). Trees may become unthrifty.
Transmission The bacteria live in soil and infect plants through wounds. Infected cells receive a cancerous factor from the bacteria, which causes them to divide uncontrollably and thus form the galls. The bacteria infect a wide range of plants, particularly woody perennials.
Favoured by Continued in-ground planting of susceptible hosts. More prevalent on young nursery stock. Wounding by grafting, budding, cultivation etc.
provides entry points for the bacteria.
L: Galling at soil level on potted olive tree R: Galling on lower roots of olive seedling
© SARDI © NSW DPI
40 Leaf mould Cause Fungus: Pseudocercospora (= Cercospora = Mycocentrospora) cladosporioides Alternative names Cercospora leaf mould, olive leaf spot, cercosporiosis Symptoms Grey mouldy blotches develop on the underside of the leaves. The tops of the leaves turn yellow then brown, then leaves fall. Often occurs together with peacock spot, causing signiﬁcant defoliation and damage to new growth and reduced crop production. Fruit are rarely infected, but, if so, show round, reddish-brown spots.
Transmission Overwinters in old infected leaves.
Usually infects in autumn, targeting the young spring growth.
Favoured by High humidity and rain, 12–28 °C.
L: Grey mouldy blotches on underside of yellow to brown leaves R: Mouldy appearance from fungal spores
41 Nematodes Root knot nematode, Meloidogyne sp.
Citrus nematode, Tylenchulus semipenetrans Root lesion nematode, Pratylenchus spp.
Symptoms Vary from unthriftiness to stunting and leaf yellowing. Root knot nematodes cause distinctive root galling.
Transmission Soilborne organism, spread with movement of soil, water and infected plants.
Favoured by Soil that previously grew host plants. For example, citrus and root lesion nematodes are common in old citrus land, and root knot nematode is common in old vegetable soil. Damage would be expected to occur with high populations.
Root galls caused by root knot nematode © NSW DPI 42 Olive knot Cause Bacterium: Pseudomonas savastanoi pv. savastanoi Symptoms Rough galls or swellings of variable size occur on twigs, branches, trunks, roots, fruit or leaves.
Galls can appear either singly or close together. They are most common on twigs and young branches, but will also form around wounds on the main trunk. Starting as small swellings 3 to 5 mm across, they grow rapidly into smooth, spherical green knots, increasing in size as they mature and becoming darker and more furrowed.
Transmission The bacteria live in the galls and ooze out in wet weather. They enter the tree through wounds, including leaf scars, damage by hail and frost, pruning wounds or wounds caused during harvesting.
Favoured by Trees at most risk are those with wounds during periods of rain. Some cultivars are more susceptible, e.g. ‘Barnea’, ‘Frantoio’.
Note Olive knot has not been detected in all states. If you see symptoms, notify your state agriculture dept.
Above L: Young and older galls on olive branch Below L: Galling around wound R: Bacteria inside olive knot © AQIS
43 Peacock spot Cause Fungus: Spilocaea oleagina Alternative names Olive leaf spot, bird’s-eye spot Symptoms Round spots from 2 to 10 mm in diameter on the upper surface of the leaf, and occasionally on stems and fruit. Spots ﬁrst appear as small pale blotches, later becoming muddy green to black, often with a yellow halo. Spots on underside of leaves are grey.
Severe infection may cause defoliation, which can kill new wood and reduce production in the following year.
Young leaves may remain symptomless.
Transmission Fungus overwinters in old infected leaves. Spores germinate in free water and are blown or splashed onto the leaves. Movement between trees is limited.
Favoured by High humidity and rain. Usually occurs sporadically, particularly in wet weather in spring.
Disease is inactive during summer.
44 Phytophthora root rot Cause Water mould: Phytophthora spp. (several species) Symptoms Root and crown cankers that may extend up the trunk. Leaves wilt, yellow and may drop. Trees may die suddenly, or slowly decline over several years.
Sudden death is common when stress is placed on the tree, such as during ﬂowering, fruit development or hot weather.
Transmission Soilborne organism, spread by movement of soil, water and infected plants.
Favoured by Phytophthora root rot is consistently associated with excessively wet soils, clay-panning (p
50) or poor drainage. Care must be taken when using feral plants as rootstocks, as many grow in areas where Phytophthora is present in the soil.
L: Crown canker on 5year-old tree R: Severe rotting of roots and lower stem
46 Verticillium wilt Cause Fungus: Verticillium dahliae Symptoms One or more branches wilt, usually early in the growing season. Dead leaves remain on the tree.
Roots are repeatedly infected over several seasons and trees gradually die. Internal tissue of lower stems may darken as the fungus disrupts the ring of sap-carrying tissue under the surface. Olive cultivars vary greatly in susceptibility, and symptoms may not be seen for 4 to 8 years after planting. Another form of this fungus in Europe causes defoliation.
Transmission Soilborne. The fungus survives in soil for many years and can infect the roots of a wide range of plants. It can spread in irrigation water and infected soil on farm machinery and tools.
Favoured by Cool and moist soils when daytime temperatures range between 20 and 25 °C. Suppressed by higher temperatures. Common in land where alternate hosts (e.g. cotton, lucerne, brassicas) have been grown.
L: Mature tree with wilted branch R: Young tree with wilted branch Inset: Darkened ring of water-conducting tissue inside stem
© NSW DPI© SARDI © NSW DPI
47 Wound cankers Cause Opportunistic wound invaders Fungi: e.g. Botryosphaeria sp., Pycnoporus coccineus (white wood rot) Bacteria: e.g. Pseudomonas syringae, Ralstonia solanacearum, Xanthomonas campestris Symptoms Vary from slow decline of trees and tree death to localised cankers around wound sites with occasional branch death above infection. Can also cause brown staining of the vascular (sap-carrying) system.
Transmission All are wound pathogens. Can be borne by wind, water and soil. Most are common organisms that opportunistically infect through wounds.
Favoured by Wounds, wetness and high humidity causing moisture ﬁlms around wound sites.
Top L: Entry of bacteria at pruning wound caused stem death Bottom L: P. syringae causing localised wounds at leaf scars R: Brown internal staining from Ralstonia infection © SARDI © SARDI
48 Disorders Apical end rot Alternative names Apical end desiccation, soft nose Symptoms The apical (blossom) end of the fruit shrivels, mostly close to maturity. The internal ﬂesh and pip may be blackened, either at the apical end only or throughout the whole fruit. Sometimes secondary fungal rots infect the shrivelled end.
Cause The cause is unknown. It may result from sudden changes in temperature and humidity, which produce partial dehydration of the fruit at the apical end. It has also been associated with calcium and boron deﬁciencies, and with changes in watering regimes.
R & below L: Apical end rot Below R: Rot can be internal at apical end only or throughout the whole fruit
49 Clay-panning & root plaiting Clay-panning and root plaiting are disorders in root architecture that can lead to unthrifty plants that are subject to stress-related dieback and infections.
Clay-panning is caused by poor soil structure and ground preparation, whereby a hard layer of subsurface soil prevents roots from growing downwards. Affected trees may also be subject to temporary waterlogging, which can lead to further disorders and infections.
Conversely, dry soil can exacerbate stresses, because plants cannot draw moisture from deeper in the soil.
Trees may also be subject to blowing over in strong winds because of their poorly anchored root systems.
Root plaiting occurs when plants become pot-bound during their nursery production. Plants have reduced and weaker root systems, which allow environmental stresses to lead to various disorders and infections.
L: Clay-panning R: Root plaiting
50 Sooty mould Cause Fungi: Capnodium sp. (most common);
also Fumago, Scorias & Aureobasidium spp.
The fungi are wind blown and attach to the honeydew excretions from sap-sucking insects, particularly black scale (p 22), but also aphids, mealybugs and psyllids.