Conservation farming promotesa diversity of insect life,influences pest populations andalso favours many beneficialinsects. The beneficial insectswhich act as natural controlagents help to create a morestable agricultural system.

Reducing cultivation andmaintaining a mulch provides amore favourable habitat forcertain soil dwelling insect pestsand disease organisms. A rangeof pests including caterpillars,beetles, grasshoppers, foliagefeeders and sap-sucking insectsoccur in all crops and pasturesand will require control fromtime to time.

Pest management will beachieved only by a long termcommitment to integratedcontrol practices. Integratedpest management (IPM) involvesthe strategic use of rotations,resistant varieties, beneficialinsects, cultural measures andselective pesticides. IPMrequires an understanding of theinteraction between pests, plantsand the environment. IPM willensure that chemical use andpest control is optimised,environmental contamination isminimised and production ismaintained.

Integrated pest managementinvolves:

rotating crops and pastures todisrupt pest lifecycles

selecting varieties resistant topests and disease

using strategic cultivation todisrupt the development ofpests

eradicating plants whichharbour insect pests or disease

monitoring crops to determinepest and beneficial insectactivity

encouraging and protectingbeneficial insects

applying pesticides only whenpests approach economicinjury level

using selective or 'soft'pesticides which target pestsonly

COMMON INSECT PROBLEMS

Insect Pests and CropEstablishment

Soil dwelling pests such asearwigs, scarab beetles, falsewireworms, winglesscockroaches and cutworms areactive in or on the soilparticularly under high mulchlevels. They feed on the rootsand shoots of emergingseedlings. Insect numbers anddamage levels will vary fromyear to year according toseasonal conditions.

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12. INSECT PEST AND

DISEASE MANAGEMENT

12.1 INTEGRATED PEST MANAGEMENT THE LONG-TERM SOLUTION

Control of soil borne pestsinvolves seed treatment with anappropriate insecticide or an in-furrow insecticidal spray orgranule at planting. Acommercial bait is available forthe control of surface insectpests. Presswheels or seed-firming wheels will allow morerapid germination and may helprestrict the movement of insectsthrough the soil.

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False wireworm is the mostcommon and damaging insectpest of crops and pastures atestablishment. Damage iscaused by the larval orimmature stage feeding ongerminating seeds but adultsmay also feed on seedlings.

Some soil dwelling insects can bedetected prior to planting byplacing baits of pre-soakedsorghum grain at several sitesthroughout the field. Baits aredug up and inspected after theseedlings emerge. The numberof insects found gives anindication of expectedpopulations and one or moreper bait usually indicate thatcontrol may be necessary.

Plate 86Courtesy of DowElanco. Soil dwelling insect pestscan cause significant damage to establishingcrops.

(1) Click beetle (adult true wireworm)Length 913mm.

(2) False wireworm have hard, round bodies with apointed, upturned tail segment (pie-dish beetlelarvae). Length about 3.5cm when fully grown.

Field cricket. The adults and immaturestages, feed at night on the leaves andstems of seedlings and young plants.They also feed on the flowers, developingfruits and seeds mature plants.

Wingless cockroach. These insects aremost active during the summer monthscausing crop damage at night bychewing seedlings off at ground level.

Black field earwig. These insects feed on thegerminating seed and roots of young plants,killing or weakening them. This damage cancontinue until the plants are 60cm high and canresult in severe crop lodging. Damage mostlyoccurs in areas with heavy black soils.

In-furrow application of insecticide for soildwelling insect control.

(2) A wireworm with soft, semiflattened body anda forked toothedge tail segment. Length up to2cm when fully grown.

(1) Piedish beetle (adult falsewireworm) Length 1619mm.

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Grasshoppers, yellow-wingedlocusts and various caterpillarshave occasionally damagedsorghum and maize crops atestablishment. Problems mayarise in no-tillage areas whereimmature hoppers move fromthe dying mulch to emergingcrop seedlings. Damage at thisstage is swift and monitoring isessential to identify the problem.Armyworm caterpillars havealso caused sporadic damage toyoung sorghum crops in someseasons.

Foliage feeders, sap suckers,pod and grain pests

Grasshoppers, beetles,caterpillars, flies, aphids, planthoppers and pod-sucking bugsattack the foliage, flowers, podsand seed of crops and pastures.Some insects are specific andfeed on only one type of plantwhile others attack a wide rangeof crops.

Helicoverpa caterpillars(formerly heliothis) attackseveral crops, includingsorghum, maize, peanut,sesame and most grainand pasture legumes.Sorghum midge is aspecific pest of grainsorghum.

The most common insectpests are Helicoverpaspp., other caterpillarsand pod-sucking bugssuch as the greenvegetable bug, red-bandedshield bug and Riptortus

spp. Pod-sucking bugs areparticularly damaging tolegumes such as mungbean,soybean and Cavalcade andBundey seed crops.

MONITORING PESTS ANDDECIDING ON CONTROL

Crops vary in their tolerance toinsect attack depending on thetype of damage and stage ofgrowth. Seedlings have littletolerance to insect attack andrelatively small numbers cancause economic damage. Mostcrops can withstandconsiderable insect pressure inthe vegetative stage butconsiderably less damage atcritical growth stages such asestablishment, flowering, grainfill and pod maturity.Monitoring and managementduring these high risk periods isessential to minimise economicloss.

Plate 87a, b(a) Yellow winged locusts.(b) Damage to a sorghum

crop.

aa bb

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The first step in managing pestsis to establish which insects, andhow many are present.Monitoring involves regularinspection of crops. Insect pestsare usually present but, in mostinstances, in numbers too low tocause economic damage orwarrant control. Monitoringavoids unnecessary use ofpesticides and allows informeddecisions to be made based onactual pest numbers and damagelevels, rather than guesswork.Monitoring involves countinginsect numbers in a given area(ie. 5 m of crop row) at severalsites throughout the field.Guidelines regarding insecttolerance levels have beenestablished for most crops.

Plate 88Monitoring crops, especially atflowering, is essential foreffective pest management.

Beneficial insects suchas predators andparasites are importantnatural control agentsand play a major rolein reducing pestnumbers. Only whennatural control isabsent or pest numbersgrow beyond thecapacity of naturalagents, do othercontrol measuresbecome necessary.Beneficial insects are avital part of integratedpest management andinclude beetles, bugs, ants,wasps, spiders, earwigs, flies,mantids, lacewings anddamselflies.

Identifying the pests, theirdamage and knowing when theyare likely to attack the crop isessential for effective insect

management.

Plate 89a, bBeneficial insects such as(a) the Predatory shield bug and(b) Assassin bug play a major role in reducing

insect pest numbers. Both predators arefeeding on heliothis.

aa

bb

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Plate 90a i, ii(i) Red-banded shield bugs and(ii) Green vegetable bugs are serious pests of grain and pasture

legumes.

Plate 90b i, ii(i) Heliothis caterpillars on sorghum

head and(ii) Northern armyworm is a sporadic

pest, while heliothis are a frequentpest of most crops of the Top End.

ii

iiii

ii

iiii

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Plate 90c i, ii(i) Riptortus feed on pasture seed crops and grain legumes and(ii) Crusader bug (with a straight proboscis, characteristic of

plant-sucking bugs).

Plate 90dGrain sorghum damaged by sorghum midge.The insect is usually prevalent in irrigated crops.

iiii

ii

dd

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Plant diseases include manyspecies of fungi, bacteria,mycoplasmas, viruses andnematodes. Some diseases aretransmitted by vectors such asinsects, fungi or nematodes.Development of disease dependsupon a number of factors and ifone or more of these are absent,disease will not develop or willbe reduced in severity.

Disease development dependsupon:

Susceptibility of the crop orpasture to disease

The presence of a virulentdisease organism

Environmental conditionsfavourable for infection anddisease development

Townsville stylo (Stylosantheshumilis), a legume similar toVerano and Amiga stylo, whichwas planted over vast areas ofthe NT and north Queenslandwas devastated by anthracnose(a leaf and stem disease causedby the fungal pathogenColletotrichum gloeosporioides)in the mid-1970s. Large areas ofstylo pasture were wiped out,illustrating the damage whichcan be caused by a virulentplant disease.

New species with better diseaseresistance have since beenreleased but there is still athreat that a new race ofanthracnose may develop andinfect one or more of the currentstylos. To combat this threat, itis recommended that a numberof stylos (ie. Seca, Siran, Veranoand Amiga) be sown in a mix sothat if one should succumb todisease the others will persistand remain productive.

The retention of mulch mayfavour the build up of certaindisease organisms which causeleaf spots and stem and headrots. These can damage cropswhen conditions are favourable.Burning crop residues to reducedisease has been practised inother agricultural areas inAustralia but current experiencesuggests this practice isundesirable in the Top End dueto the negative impact ofreducing soil surface cover.

12.2 DISEASE IN CROPS ANDPASTURES

Plate 91a, b(a) Sorghum affected by charcoal

rot (Macrophomina phaseolina). (b) Stem disorder caused by the

disease.

bb

aa

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Conservation tillage can reducethe incidence of certain diseasesby improving the conditions forcrop growth and therebyincreasing resistance toinfection. Fungal diseases suchas charcoal rot (Macrophominaphaseolina) and stalk rot ofgrain sorghum (Fusariummoniliforme) are accentuated byhigh soil temperatures andmoisture and nutrient stress.Maintaining mulch, goodnutrition, weed control andresistant varieties will reducethe incidence of such diseases.

Disease management, like allpest management, requires anintegrated approach andstrategies include:

crop rotation

use of resistant and adaptedvarieties

correct planting time andagronomy

insect vector control

adequate soil fertility andappropriate pH

use of fungicides and seeddressing

management of mulch levels

strategic tillage

quarantine to prevent diseaseentry

farm and machinery hygiene

COMMON PLANT DISEASES

The most common diseases incrops and pastures are foliarand stem diseases. Head andgrain moulds in sorghum mayoccur in prolonged wet weatherbut are of minor importance.Seed and seedling rots can occurbut are largely controlled byfungicide treated seed.

Leaf spots, blights and ruststhrive in prolonged wet weatherand high temperatures.Cercospora leaf spot in peanutand blast in rice can beparticularly damaging in certainseasons. Leaf spot survives inseed and old peanut debris.Control involves crop rotation toreduce inoculum, sowing non-infected seed and applyingfungicides immediately thedisease is evident. Rice blast isa leaf and stem disease whichsurvives on rice stubble.Burning stubble will reduceinoculum levels but resistantvarieties and rotation offer moresustainable long-term control.

Plate 92Wallaby-ear virus transmitted by aleafhopper insect in irrigated maize.

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Many soil borne organismsinfect plants when conditionsfavour their development. Suchdiseases include charcoal rot ofsorghum and stem blight ofmungbean, sesame and soybeancaused by Macrophominaphaseolina. Plant diseasesoccur sporadically and althoughnot of major economicimportance in the Top End atpresent, the potential for diseasewill increase as farming andirrigation intensifies.

Conservation farming systems willhave no more and possibly less

insect and disease problems thanconventional farming.

Plate 94Powdery mildew onmungbean grown underirrigation in the dry season.

Plate 93Cercospora leaf spot is a serious disease ofpeanut and builds up on successive crops.