Field pests
Damage from field insects is not generally a major factor for oat crops, however there is a zero tolerance to insects in export hay. Significant damage can occur if insect populations build up.
Planning rotations to minimise pest carryover, timely sowing, adequate crop nutrition and good control of weed and root diseases will all assist in reducing the likelihood of crop attack by insect pests.
Check crops regularly throughout their growth for field insects. Control redlegged earth mite and lucerne flea during the seedling stage if necessary. Aphids should be checked for and controlled from flag leaf stage and later in crops considered to be high yielding. Aphids can also transmit barley yellow dwarf virus (BYDV). If growing susceptible varieties in areas with moderate to high BYDV risk then spraying the crop with a synthetic pyrethoid at 4-5 weeks after sowing is advisable.
Correctly identifying the insect is critical for their successful management.
Cockchafer
Crop stage
Before seeding.
Description
There are several important pest species and adults range in size from 5-20mm. Adults are usually brown or blackish beetles. The beetles fly readily and are attracted to lights. Cockchafer larvae are characteristically 'C' shaped creamy white grubs ranging from 2-25mm long.
Life cycle
The complete life cycle may take one or two years. Some species have a long larval stage which extends over 12-18 months. In most species the larva is active during late autumn and winter. In these species pupation occurs in spring and adults emerge in early summer. Feeding, mating and egglaying may occur throughout summer.
Damage
Cockchafer larvae feed underground and some species are serious pests which may cause patches and poor growth in pasture and may slow growth or kill large areas of cereals and lupins. Young plants without extensive root systems are worst affected. The adult beetles are also very destruction as they feed on tree foliage.
Control
Control of cockchafer larvae is rarely warranted. The pest species in this state cannot be controlled with chemicals after planting as the larvae remain underground. Cultivation, shallow planting and a high seeding rate may help to overcome the problem. The problem is most serious when early growth is slow. Large populations may be present under young crops and in pasture without causing significant damage.
Desiantha weevil
Crop stage
Before seeding, seedling.
Description
The larvae are white, legless creatures 6mm long and with orange-brown heads. They remain under the soil and are difficult to locate although some painstaking digging may reveal the larvae close to plants. The adults are grey-black weevils approximately 5mm long with the typical weevil snout.
Life cycle
Eggs are laid in autumn and hatch after opening rain and the larvae commence feeding on young pasture seedlings. When cereal crops are planted into heavily infested paddocks, they are attacked by the larvae which may be well grown. In spring the larvae pupate and become adults, which are grey-black weevils approximately 5mm long with the typical weevil snout. The adults are common in spring and summer hiding under wood or stones or they may be found on cereal heads and can be harvested with the grain.
Damage
Desiantha weevil is a sporadic pest of cereal seedlings in south coast areas. It is the larval stage which can completely destroy hundreds of hectares or may affect smaller areas by feeding on underground parts of the seedlings. Plant growth may be slowed or plants may wilt and die in which case they may be easily pulled from the soil.
Control
Control with chemicals is not possible after planting. The problem is most likely to occur where shallow sand occurs over gravel or clay. As larvae will be larger following summer rain, crops should be planted early and shallow to minimise attack. Where the pest is confirmed, planting with treated seed at 90 kilograms per hectare (kg/ha) is recommended.
Cutworm
Crop stage
Before seeding, seedling.
Description
There are several species (Agrotis infusa, A. munda, various other species) in this state which vary in appearance but the larvae are all smooth and plump. The larva of the most common species, the pink cutworm, is grey-green with a pink tinge and is usually found in sandy soils. The larva of another common species, the bogong moth, is dark grey. The larvae usually hide by day but may be found under the surface and often close to a damaged plant. They curl up when disturbed. At times, brown cutworms with a herringbone pattern along the back, damage crops. In south coastal areas they are more likely to be found on the soil surface by day, than are the pink or black cutworm. The adult moths of herringbone cutworm are of various species, and range from black, through grey to brown. Occasionally, autumn attack by armyworm in cereals resembles cutworm damage. This is significant, because armyworm are harder to kill with insecticides than are cutworm.
Life cycle
Eggs are laid on the soil or on plant material close to the ground. The larva may grow 50mm long before becoming a pupa and then the adult moth. The adults are stout-bodied, with a wing span of up to 40mm. The forewings are patterned brown or dark grey. Several generations are possible in one season.
Damage
As the name implies, the cutworm chews through plant parts, often felling the plant at ground level. Just two or three large caterpillars would seriously damage a square metre of crop and almost all crop and pasture plants are susceptible to attack. This is not a regular pest but large areas may be affected.
Control
The weather and food supply are the most important factors in determining abundance. Biological control, such as by fungal diseases, may be spectacularly successful, while wasp and fly parasites are also very active in preventing more frequent and serious outbreaks.
Webworm
Crop stage
Before seeding, seedling.
Description
Webworm caterpillars are seldom seen as they come above ground level only when conditions are cool and damp and usually at night. They may be located in their web-lined tunnels from which plant parts may be seen protruding. The caterpillars are pale to deep brown with a tinge of the green gut contents showing through. The head appears black or dark brown. Fully grown caterpillars are about 15mm long.
Life cycle
Caterpillars hatch from eggs laid amongst grass in autumn and feed throughout the winter. Spring and summer are passed in the tunnels as resting stage caterpillars. After this, the insects proceed through the pupal stage and emerge as adult moths, which are about 10mm long and may be seen flying in large numbers on autumn nights. By day they hide in dry grass, the colour of which they closely resemble.
Damage
Large areas of emerging wheat or barley crops may be destroyed by the continual chewing damage of a heavy webworm infestation. The caterpillars sever leaves or whole plants which they scatter on the ground or pull into holes near the plants. In pasture, the grass component may be removed from large areas.
Control
The paddock condition in autumn and the weather are very important in determining webworm numbers. Eggs will not be laid in great numbers and will not survive well in a bare paddock or in stubble. Grassy situations favour survival. Cultivations leading to a weed free paddock over a three week period destroy the young stages but reduced tillage cropping methods allow a greater survival. Hot and dry conditions during May and June, resulting in a lack of feed, could destroy most webworms. If a quarter of the plants is being seriously damaged at or just after emergence, spraying should not be delayed as the continued feeding will kill many plants and result in bare ground or thin areas.
Red legged earth mite
Crop stage
Before seeding, seedling.
Description
Adult mites are about the size of a pinhead (up to 1mm). They have velvety black bodies and eight bright orange-red legs. The mites are often gregarious and are found clumped together in large numbers. They disperse quickly when disturbed.
Life cycle
Mites hatch from over-summering eggs in autumn when adequate moisture and low temperatures occur. Eggs produced through the season are thin-walled and hatch immediately, and several generations may develop over winter and spring. As pastures begin to senesce, the mites produce thick-walled eggs which resist drying over summer and carry the mite through to the next season.
Damage
Large numbers of redlegged earth mite are commonly found in annual pastures at the break of the season and may cause heavy loss of subterranean clover and annual medic seedlings. These species are susceptible throughout the growing season, and can suffer losses in drymatter (10-80%) and seedyield (20-80%) in spring. The greater the legume content of pastures and the lighter the grazing pressure, the higher the risk of loss from mites. They also attack lupins, rape, field peas, serradella (cotyledons only) and vegetables, but normally do not affect grasses or cereals severely. Mites rupture cells on the surface of leaves and feed on exuding sap; affected leaves look silvered, but do not have holes as with lucerne flea attack. Mite damage to seedlings is more severe if plant growth is slowed. This could be caused by cold and/or waterlogging, low seedling density after a false break, low seed banks after a crop, or if pastures or stubble are being reseeded. Capeweed increases their reproductive potential, and legumes in paddocks with a lot of capeweed may be severely damaged, especially where mites can attack smaller clover and medic seedlings from the shelter of large capeweed plants.
Control
Treating seed with a systemic insecticide before sowing pastures or crops protects seedlings from attack. Post-emergent sprays are also effective. Use systemic chemicals if more than 60% of plants have emerged. If few plants have come up and cotyledons are damaged as they emerge it is more effective to use a contact insecticide. Mite control in dense spring pastures may require higher rates of insecticide than are effective on seedlings in autumn. Hard spring grazing reduces damage. Biological control is being promoted by collecting a predatory mite, the anystis mite, from original CSIRO establishment sites and spreading it throughout the agricultural region. Establishing this predator depends on careful handling during collection and transport, and on ensuring there are areas of adequate dry plant cover in paddocks for shelter over summer.
Balaustium mite
Crop stage
Seedling.
Description
The balaustium mite has a greyish/red body , red legs and looks similar in appearance to the redlegged earth mite. If viewed under a magnifying glass or microscope short stout hairs can be seen covering the body. The adult balaustium mite grows to almost twice the size of redlegged earth mites.
Life cycle
Require rainfall before over-summering eggs can hatch. Newly hatched nymphs have six legs and are an orange colour. Development from egg to adult takes about 5-6 weeks. Several generations can occur each year.
Damage
Although balaustium mites are seen in pastures and occasionally crops it was not until 1997 that reports were received of them being an economic pest. A few properties west of Raventhorpe and some in the Esperance area have had cereal, lupin and canola crops severely bleached and wilted to the point of death from this pest. Mite numbers from 20-50 per seedlings were recorded on barley at the three leaf stage. Mites feed on the leaves of plants by probing into the surface cells with their mouth parts, and sucking out sap. High risk situations: Reports indicate that crops sown into paddocks which were in pasture last year, with high levels of broad leaf weeds, especially capeweed, will be most at risk from mite damage.
Control
In most situations crops will not require spraying and balaustium will cause little or no damage.Early control of summer weeds in paddocks that are to be cropped will prevent the build up of mite populations. Weeds present in paddocks prior to cropping should be checked to determine the numbers of balaustium mites present. If they are found in very large numbers then the incorporation of insecticide with herbicide immediately prior to sowing is a more effective control strategy than spraying when the crop is emerging and has very little cover of green material. No chemicals are currently registered for control of balaustium mite. Farmer trials have shown high rates of synthetic pyrethroids can be effective, however they can be difficult to kill. High rates of dimethoate, omethoate, chlorpyrifos and phosmet have been found to be ineffective in controlling these mites.
Bryobia mite
Crop stage
Seedling.
Description
The adults mites are slightly smaller than a pin head with a dark grey body and pale red/orange legs. They are easily confused with red-legged earth mite and are difficult to separate without the use of a hand lens. Redlegged earth mites are not usually present in early autumn as they have a cold temperature requirement before hatching. The front pair of legs on bryobia mite are very long and held out in front of the body like a pair of feelers. The body of the mites is rounded and plump. However, if starved it's body shape changes to become flat on the top and rounded underneath with a flange around the sides.
Life cycle
Adult bryobia are active in late spring, summer and autumn. Eggs are present over winter, and hatch as conditions dry and warm up in spring and early summer. Winter eggs are usually laid in batches, while eggs over the dry period are laid singly on backs of leaves of host plants. Nymphs newly hatched have six legs and are bright red, but turn dark/grey in a few days. They moult to an eight legged nymph, then again to become a third stage nymph, before finally moulting to the adult stage. A month from eggs hatching to young adult is usual. There are several generations per year.
Damage
Bryobia mites have caused severe damage, when in high numbers, to emerging canola and lupin crops in autumn. Mites feed on the tops of leaves by stabbing into the surface cells with their sharp mouth parts, and sucking out sap. Whitish grey spots result, giving leaves a stippled wilted look. High risk situations include summer rains followed by warm mild autumns, giving bryobia mites the best conditions for survival and increase. They don't tolerate cold wet weather but can persist into June following warm autumn conditions. Crops planted into paddocks with a history of summer/early autumn weeds and warm dry conditions after crop emergence are most at risk. Reports of bryobia damage have increased since 1995, before which they were considered a minor and sporadic pest in some southern districts. Bryobia were reported as being a serious pest in central and some northern cropping zones during the autumn 1998 and 1999. The use of minimum tillage, earlier sowing times and tolerance to some insecticides have led to the increased importance of this pest.
Control
Early control of summer weeds in paddocks that are to be cropped will prevent the build up of mite populations. Weeds present in paddocks prior to cropping should be checked to determine the numbers of bryobia mites present. If they are found in large numbers then the incorporation of insecticide with herbicide immediately prior to sowing is a more effective control strategy than spraying when the crop is emerging and has very little cover of green material. Omethoate is registered for control of bryobia mite in pastures and some crops. Rates of insecticides commonly used to control redlegged earth mite and lucerne flea are not effective against bryobia mites.
Lucerne flea
Crop stage
Seedling.
Description
Lucerne fleas usually spring from the plants when approached, using a special organ situated underneath the body. The lucerne flea is a dumpy looking and wingless creature of varied colour, but the larger specimens of 2-4mm are predominantly green or yellow.
Life cycle
The first soaking autumn rains cause the special over-summering egg batches to hatch. Several generations may then develop over the growing period depending upon the weather. Eggs are laid in the soil and usually hatch in a few days. With the onset of warm and dry conditions in spring, the resting stage eggs, which are able to withstand summer conditions, are laid.
Damage
Pastures, legume crops and cereals may be seriously retarded by the lucerne flea and seedling death may occur in heavy infestations. Frequently the green leaf tissues are eaten, leaving a surface of the leaf as a whitish film. Severely affected areas appear, from a distance, to be bleached.
Control
The lucerne flea is favoured by heavy soils and cannot live in very sandy situations. It is also dependent on plentiful moisture. Control in crops and pastures may be obtained with systemic or contact insecticides, as discussed under redlegged earth mite. A predatory mite, the bdellodes mite, is present over most of the area occupied by lucerne flea and exerts a useful level of control. Another predatory mite, the neomolgus mite, was introduced by the CSIRO and has been released at many places in the agricultural area. It will extend the area and level of biological control.
Cereal aphids
Crop stage
Tillering, flowering to maturity. BYDV transmission.
Description
Corn aphid (Rhopalosiphum maidis) and wheat/oat aphid (Rhopalosiphum padi) cause most yield loss. Wingless females are about 0.2-2.5mm long. Rice root aphid (Rhopalosiphum rufiabdominalis) and grain aphid (Sitobion miscanthi) are also found in cereals and may be important as virus vectors. Corn aphids are dark blue- green to grey-green, often with a fine white powdery dust over the body. Colonies develop within the furled tip of tillers, starting any time from seedling stage to head emergence. Few farmers see them because they are hidden in the furled leaves. Barley is most likely to be affected. Corn aphid probably kills tillers, resulting in fewer heads. Wheat/oat aphids vary from mottled yellow-green through olive-green and dusky brown, to a blackish green.
Colonies develop on the outside of tillers from the base upwards, on stems, nodes and backs of mature leaves, starting any time between late tillering and grain filling. Heavy infestations can blacken heads and flag leaves, and are the aphids most commonly reported by farmers. Wheat/oat aphids are more mobile than corn aphids, and can drop to the soil and crawl to other plants. They cause yield losses probably by reducing grain weight and grains per head. They may also be important in spreading BYDV. Rice root aphids are like wheat/oat aphids, but can also infest plant roots. They have a reddish patch in the middle of the back, and are most likely to be found in drier agricultural areas. Grain aphids are dusky green with yellow-green tinges, usually found in spring, without developing large colonies. Rose-grain aphids are potentially serious pests, but are yet to enter Western Australia from the eastern states where they are widespread. They are green spindle-shaped aphids attacking wheat and barley during grain filling.
Life cycle
Winged aphids fly into crops from pasture grasses or other crops, and start colonies of wingless aphids. Reproduction is rapid when weather conditions are favourable, leading to population outbreaks. Plants can become sticky with honey- dew excreted by the aphids. When plants become unsuitable or overcrowding occurs, winged aphids redevelop and migrate to other plants or crops. They can carry viruses in saliva or on their feeding tubes. BYDV damage is most serious after plant infection early in the season.
Damage
Cereal aphid damage in barley, wheat and oats has no obvious signs or symptoms. Research in medium and high rainfall zones has shown aphids can cause losses up to 30% where crop yield potential is three tonnes per hectare (t/ha) and higher. Experimentally, losses of 400-1800kg/ha have been measured in barley yielding about 5t/ha. As this work is new, some questions remain unanswered. Damaging populations may develop in three out of five years. Aphids affect cereals by direct feeding on plants, and/or by transmitting barley yellow dwarf virus (BYDV). BYDV affects wheat, oats and barley and is spread by flying aphids. Direct damage occurs when colonies of 10-100 aphids develop on stems, leaves and heads, from seedling stage through to head filling. The degree of damage depends on the percentage of tillers infested, aphids per tiller, and the duration of the infestation.
Control
In southern areas, barley crops should be checked from late tillering onwards for corn aphids in the furled growing tips, and for wheat/oat aphids on stems, backs of leaves and in the crown. Crops expected to yield 3t/ha or more are most at risk. Spraying is worthwhile if 50% of tillers have 10-20 or more aphids. Mixed infestations of both aphids may cause more damage than either species on their own. Crops sprayed before Zadoks stage 30 may need respraying at Zadoks stage 50 or later, if aphid numbers build up again. Parasitic wasps, ladybeetles, lacewings and hoverflies can provide useful biological control, mainly by preventing secondary outbreaks. The use of "soft" insecticides that only kill aphids is advocated.
Armyworm
Crop stage
Flowering to maturity.
Description
There are four species of armyworm in Western Australia - the common armyworm, the southern armyworm, the inland armyworm and the sugarcane armyworm. Of these, the common armyworm is the most damaging. Moths are stout bodied, grey to cream, with a wingspan of about 40mm. They fly at night and are strongly attracted to lights. Armyworm caterpillars vary in colour depending on their numbers in a crop. If there are many caterpillars in a crop then they become dark while if the population is low, the caterpillars are much paler. Armyworms are about 40mm long when fully grown and can be distinguished from cutworms and budworms by their large heads and by three prominent white stripes on the 'collar' behind the head. Often the armyworms themselves will not be seen as they feed mainly at night but their droppings, which look like small green square hay bales, will be obvious on the ground below the crop canopy. Another indicator that armyworms are present is damage to ryegrass seed heads.
Life cycle
Armyworms have three or four generations per year and on the south coast they survive over summer on self sown cereals and grasses that germinate with summer rains. In spring it takes about three weeks from when the eggs are laid for them to hatch and for the caterpillars to reach head lopping size. Once damage begins many heads can be lopped in a short time.
Damage
Armyworms are regular pests of coarse grain crops on the south coast and occasional pests in inland areas. Towards the end of spring, when crops are approaching maturity, large armyworm caterpillars chew through the stem of barley just below the head, causing the head to fall to the ground. If in large numbers earlier in the season, they may eat leaves and be confused with cutworm.
Control
Heatwaves may kill most of the caterpillars. Native parasites can exercise good control and spraying is not normally required every year. Several wasp parasites including Apanteles ruficrus have been released to increase biological control.
Australian plague locust
Crop stage
Flowering to maturity.
Description
Newly emerged nymphs are about the size of houseflies and hop actively. Adults have a characteristic black tip to the hind wing. Swarming locusts are light brown, but solitary individuals may be green or yellow.
Life cycle
Two generations occur annually. Nymphs of the first generation appear when soil temperatures begin to rise in spring. The attainment of adulthood may take four to eight weeks depending on climatic conditions. Eggs laid by the first generation require at least three weeks to hatch and will only hatch if sufficient soil moisture is present. Eggs laid by the second generation enter a resting phase which enables them to over-winter.
Damage
Adult locusts will eat almost any green plant material, but crops most at risk are ripening cereals in early summer, summer pastures and green pasture growth following summer rain. Farm gardens may be severely attacked. Locust plagues in Western Australia are rarely as severe as those in the eastern states.
Control
Egg parasites are common but rarely cause significant losses. Several fly parasites are common and the second locust generation is often heavily parasitised. The species is declared under the Agriculture and Related Resources Protection Act and control is obligatory.
Stored grain pests
Grain insects are not permitted in export grain or grain for sale. Protecting your grain intended for use on-farm from insect attack saves money.
- Even light infestations of weevils can reduce germination of the grain.
- Weevils eat or contaminate food intended for livestock.
- Weevils over-wintering in stored grain can re-infest machinery.
Grain stored on-farm will eventually become infested with grain beetles or moths unless specific control methods are undertaken. Good hygiene is critical. Other options include:
- cooling grain with aeration
- fumigating a sealed silo with phosphine generating tablets
- applying a malathion insecticide
- treating grain by mixing with Dryacide.
Aeration will suppress insect populations but not totally eliminate them. If delivering grain to a nil tolerance market, farmers will eventually need to fumigation.