Parasitism levels appear to be a little down from last year, but still good levels have been recovered. Parasitism so far has ranged from 50-90% in Emerald, 35% in St George, 20% on the Downs and 10% in lower Namoi.

Whitefly parasitoids are small wasps. There are two parasitoids that are commonly encountered in cotton, Eretmocerus and Encarsia. Eretmocerus hayati was released for biological control of whitefly in cotton and horticulture and is the most effective and abundant parasitoid in the cotton system.

The parasitoid wasps attack early instar whitefly nymphs. The female wasp is capable of laying hundreds of eggs which she deposits individually underneath the nymphs. When the parasitoid larvae hatches, it tunnels into the whitefly and eats it from the inside–out.

Identification of Parasitised Whitefly

Unparasitised whitefly nymph

• Early juvenile stages will be clear with two red eyes and two bright yellow organs (mycetomes) at the tail end (fig. 1).

• As the nymph reaches late 4th instar it will change from clear to a bright yellow with white spots appearing as the wings form (fig. 2).

• The exuviae (or spent pupal case) will be a transparent white (fig. 1).

Figure 1. (left) Early 4th instar whitefly nymph and two exuviae (spent pupal cases).
Figure 2. (right) Late 4th instar whitefly nymph.

Parastised whitefly nymph

• Nymphs are dull or dirty yellow/brown – Eretmocerus parastioid (fig. 3)
or
• Nymphs are dark brown or black – Encarsia parastioid (fig. 4)

• Sometimes the dark semi-circle of the developing parastoid larvae is visible (fig.5).

• Myecetomes appear non-symetrical or irregular.

• Exuviae is ‘dirty’ in appearance.

• Exuviae has a round exit hole where the wasp parasitoid has chewed its way free of the dead whitefly.

Figure 3. (left) Whitefly parasitised with Eretmocerus sp.
Figure 4. (centre) Whitefly parastised with Encarsia sp.
Figure 5. (right) Larvae of developing parasitoid visible inside whitefly nymph.

Correct use of a hand lens

A common complaint for why consultants do not check for parasitism or species composition in whitefly is that the whitefly are ‘too small’. Correct use of a hand lens will make it possible to identify species composition and parasitism.

The correct way to use a hand lens is to hold the hand lens right up to your eye, as close as your sunglasses would be (fig. 6). Then, bring the object into focus by moving the object, not the hand lens.

Often, users hold the hand lens away from their face which gives far less magnification making identification of parasitised whitefly impossible.

Figure 6.  Correct use of a hand lens requires users to hold the hand lens very close to their eyes to get the most magnification from the hand lens.

Article and images by Zara Ludgate

The exotic species of mealy bug is commonly known as the Solenopsis mealybug (Phenacoccus solenopsis).

The Solenopsis mealybug is a native of North America – first collected and described in New Mexico in 1897. In 1990, it was reported as a pest of cotton in Texas. From there it moved into Central and South America, and is now known to occur in Ghana, Nigeria, Israel, Pakistan, India, Indonesia, Thailand and China.

The Solenopsis mealybug is a polyphagous pest which means that it feeds and reproduces on a wide range of plants. In Pakistan it has been recorded on 154 plant species including field crops, vegetables, ornamentals, weeds, and trees.

Other key reasons for the fast spread and difficulty to control this pest include:

• The bugs possess a waxy coating that protects them from insecticides and natural mortality factors
• They have a high reproductive rate
• They have the ability to hide in soil cracks and crevices.
• They are spread through natural carriers such as raw cotton seeds, wind, water, rain, birds, humans, farm equipment and animals.

Identification and lifecycle of the Solenopsis mealybug
The female mealybug is wingless with a 3-4 mm long oval shaped body which is covered with white hydrophobic (water repellent) mealy wax. There are dark bare spots on the thorax and abdomen, which appear as dark longitudinal lines.

The adult male is about 1 mm long, with a grey body and a single pair of transparent wings. Two filaments of white wax project from the end of its abdomen. The adult male has no feeding mouthparts and causes no damage.

Mature females lay eggs in waxy pouches called ovisacs. Each ovisac contains between 150- 600 eggs, the majority of which are female. The eggs hatch after three to nine days into nymphs called ‘crawlers’, which are very mobile.

No parthenogenesis (asexual reproduction) is reported in the literature and therefore it is assumed that the species reproduces through sexual reproduction.

The female crawler undergoes four larval instars before turning into an adult (there is no pupal stage). The total life span of a female mealybug is 30–48 days, which includes 21 days as adult.

Male crawlers undergo three larval instars over 13–17 days before spinning a cottony cocoon in which it passes a pupal stage for 6-8 days. A male adult lives for only 3-5 days. Mealybugs can have 12–15 generations in a year.

The species (as eggs in ovisacs or in other life stages) can survive cold conditions, both on the host plant and in the soil. In warm climates, mealybugs reproduce all year round.

Mode of damage
Mealybugs have sucking mouth parts at all stages of their life cycle, which they use to extract large amounts of plant sap. During the feeding process a significant amount of sap oozes out as honeydew which forms a sticky deposit on the leaves and stem. Honeydew promotes the growth of sooty mould fungi which inhibit photosynthesis.

Symptoms of plants infested during the vegetative phase include:
• Distorted and bushy shoots
• Crinkled and/or twisted and bunchy leaves
• Stunted plants that dry completely in severe cases.

Symptoms of late season infestations during the reproductive crop stage include:
• Fewer, smaller and deformed bolls
• Reduced plant vigour
• Early crop senescence.

Mealybugs can also stain cotton lint and reduce quality hence this pest has the ability to cause damage to both the quality and quantity of cotton.

Methods of spread
Mealybugs are generally disseminated as crawlers. The crawlers can move from an infected to a healthy plant as well as infected field to adjacent healthy fields. While this type of movement is localised, bugs have the means to travel long distances and infest new areas. The waxy coating on the mealybug crawlers facilitates passive transport of the insect by sticking onto equipment, other insects (e.g. bees), birds, animals or people. Small crawlers are also readily transported by wind and rain or in water in irrigation channels. Long-distance movement through the transport of infested plants is also possible.

Ants are also a significant factor in the spread of mealybugs. In return for providing the honey dew that the ants feed on, they spread the mealybugs, protect them from natural enemies and keep their colonies clean.

Clusters of tiny crawlers – ready for dispersal  (image by Zara Ludgate)

Management of mealybugs
There are no insecticides registered for the control of mealybugs in cotton. However there are a number of management options that can reduce infestations and the overall impact of this pest.

• Mealybugs multiply on different hosts and may initially breed on weeds before migrating to cotton crops
• Weeds in and around fields should be removed.
• Do not throw uprooted weeds into water channels.
• The removal of affected plants at the early stage of infestation may reduce mealybug numbers in the rest of the crop.
• Avoid physical contact with infested plants as mealybugs easily adhere to clothing and implements.
• Practice good farm hygiene and clean all equipment that has been in affected fields.
• Consider the insecticides that are used in control of other insect pests to conserve natural enemies of mealybugs.

Trials in Pakistan and India show some promising results in terms of suitable insecticides. Insecticide trial work to control mealybug will commence in Queensland in the near future.

The main priority at this point is to try and limit further spread of the mealybug from and within the Emerald and Burdekin areas. With harvesting of crops to commence soon in the Emerald area, the Queensland Government is working closely with the cotton industry to develop wash-down and decontamination protocols for harvesting machinery. More information about these protocols will be provided in a blog next week.

Biological control
A survey in Pakistan recorded as many as nine species of predators feeding on Solenopsis mealybugs. These predators were present throughout the cotton season but their effectiveness was not sufficient to keep mealybugs under control.

In Australia, ladybird beetles and their larvae, and green lacewing larvae were abundant in mealybug-infested fields. One of the most conspicuous predators is the mealybug ladybird (Cryptolaemus montrouzieri), whose larvae look like an oversize mealybug. To date no Solenopsis mealybug parasitoids have been recorded in Australia

Meanwhile in India, a small wasp (Aenasius bambawalei) is reported to parasitise about 60 percent of the mealybug population under field conditions.

Article by Kate Charleston and David Murray.  Images by Zara Ludgate and Greg Kauter.

Whitefly samples identified from the MacIntyre and Lower Namoi areas have been 100% B biotype (SLW). Parasitism levels recorded from this area are low at this stage (between 0-10% parasitism).

Figure 1.  B biotype, Bemisia tabaci   (Photo: R. Lloyd)

Whitefly numbers are building quickly with infestation levels rising rapidly from well below threshold to threshold levels. Rainfall in the next week may assist in reducing population build up by dislodging eggs and nymphs from leaves and slowing development during cooler weather.

Whitefly infestations have put additional pressure on supply of registered insecticides. No new supplies of whitefly insecticides will be available until the week of 8 February 2010. Admiral® will be available on the 8 February and Pegasus® will be available later in February.

So what is the management strategy given the chemical shortage?

For early planted cotton, there will be no Pegasus® available in time to benefit these crops. Therefore, whether infestation levels are in the ‘suppression’ zone in the threshold matrix or the ‘IGR’ zone (see fig. 2) becomes irrelevant because the only option will be an Admiral® application.

Do not use Admiral® too early. One well-timed application of Admiral® will take the crop through to harvest. Going too early risks having to come in with another spray. Only one application of Admiral® is allowed per season under the IRMS.

For growers who already have open cotton and are above threshold, the options are:

1)      Apply Admiral® as soon as it becomes available

2)      Apply a knockdown now and follow up with Admiral® as soon as it becomes available

Provided whitefly infestation levels are not too high, delaying treatment up to 10% open cotton should not result in damage from whitefly. Given the weather forecast for rain and cooler weather in the next few days, consider waiting for Admiral® to become available. This will put you into the 3C zone, ‘IGR + knockdown’, eg Admiral® + Talstar® + PBO.

Figure. 2. Threshold Matrix for whitefly management in cotton

In a situation where hot weather is predicted and where cotton fields are looking visibly ‘sticky’, then a knockdown spray followed by Admiral® is suggested. However, a knockdown application will only give around 3 days of relief and will destroy any natural enemies that are working for you.

For later planted cotton, Pegasus® may be available for use against moderate infestations. However, as early cotton is defoliated, late cotton may be subject to mass migration of whitefly from early cotton fields and so Admiral® may again be the best option for control.

Whitefly levels in other regions

Emerald - whitefly were generally at moderate levels and were managed with a Pegasus® application that also targeted mite and aphid infestations. Parasitism levels were high ranging between 45-90% for this area.

St George – whitefly are building up with parasitism levels generally around the 35% level at this stage.

Darling Downs – there are reports of B biotype building up in the west as well as high populations of Greenhouse whitefly in the Brookstead area. Greenhouse whitefly do not cause sticky cotton so always check the identity of the whitefly as part of your management strategy.

Further References

The whitefly threshold matrix and all the information for sampling can be found on the cotton CRC website under ‘Managing silverleaf whitefly’:

http://www.cottoncrc.org.au/content/Industry/Publications/PestsandBeneficials/Whitefly.aspx

Distinguishing ‘brown’ stink bugs from each other.

 Adults brown stink bugs (Dictyotus caenosus) are shield shaped, matt brown, and smaller than green vegetable bug (GVB), about 7 – 8 mm long (Plate 1). They may be confused with glossy shield bug (Cermatulus nasalis) which is a slightly larger predatory bug, and with rice spotting bug (Eysarcoris distinctus) which is smaller (5 – 6 mm) and has two pale elongated marks on the top (Plate 1). 

  Brown stink bugs lay pale cream eggs in twin row rafts (Plate 2).

Eggs are similar in shape to GVB eggs, but egg rafts of GVB are seldom in two rows. Newly hatched nymphs are orange with dark markings and a black head (Plate 3).  These are indistinguishable from other shield bug nymphs.  As they grow they change colour to have a pale brown abdomen and transverse dark and pale markings at the centre of the abdomen (Plate 3, fourth instar nymphs pictured).

 The latest published thresholds for helicoverpa in vegetative soybeans (Rogers and Brier, 2010) show that while soybeans can tolerate damage inflicted by moderate helicoverpa populations up to 7 larvae/m2 without yield loss, severe yield loss is inflicted by populations >7 larvae/m2 at a rate 4-5 times greater than during the pod-fill stage. The conundrum therefore is that while vegetative soybeans are far more tolerant of low to moderate helicoverpa populations (< 7/m2) than podding soybeans, they are markedly less tolerant of populations > 7/m2 than are pod-filling soybeans (see Figure 1).

The reason for this severe yield loss is that unlike most leaf-feeders such as loopers, helicoverpa also attack the plant’s auxiliary buds and vegetative terminals, completely destroying these structures.

Damage to auxiliary buds potentially reduces yield as these structures are the precursors to the plant’s flowers and (subsequently) pods. Damage to vegetative terminals is potentially bad for yield. The reason for this is that while plants may compensate by setting additional side branches, pods formed on these are often closer to the ground and are more difficult to harvest.

Where helicoverpa populations are not excessive, damage is spread over a number of plants and the crop is able to recover and compensate without yield loss.

However, once populations exceed critical level in vegetative crops (about 7/m2), damage per plant reaches a critical level beyond which the subsequent plant growth is severely affected.

 To reduce the risk of severe early helicoverpa damage, the sampling guidelines have been revised to “sample crops twice weekly from the seeding stage onwards”. This more-intense sampling regime maximises the chance of helicoverpa larvae being detected while they are still small (ideally <7 mm) and thus able to be controlled with a Helicoverpa virus biopesticide, eg VivusMax or Gemstar.

Remember that the use of biopesticides in pre-flowering soybeans is a key in the “Go Soft Early” strategy to minimise the risk of silverleaf whitefly (SLW) attack in soybeans. The “Go Soft Early” strategy also promotes the build up of beneficial insects attacking other pests such as helicoverpa and loopers.

Vegetative soybean crops can tolerate populations up to 7 larvae/m2 and it is not necessary to kill every helicoverpa larva in a crop. Assuming only 70% control, even populations as high as 20 larvae/m2 can be reduced to below the critical 7 larvae/m2 level in vegetative crops.

Very small plants have fewer nodes and hence fewer auxiliary buds and a given helicoverpa population will damage a greater proportion of auxiliary buds per plant. Severely damaged plants will also be more susceptible to subsequent helicoverpa attack.

Note that small larvae often feed in leaf terminals, so inspect these and look for the tell tale damage symptoms, small holes in the leaflets and frass. For the latest guidelines about applying helicoverpa virus, refer to the previous blog of 8th January 2010. In seedling and early vegetative crops, pesticide costs can be halved by banding the spray over the crop, and blocking off nozzles over the bare inter-row.

References:
Rogers D.J. and Brier H.B. (2010). Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on vegetative soybean. Crop Protection 29(1): 39-46.
Rogers D.J. and Brier H.B. (2010). Pest-damage relationships for Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on soybean (Glycine max) and dry bean (Phaseolus vulgaris) during podfill. Crop Protection 29 (1): 47-57.

Article by Hugh Brier. Images by Hugh Brier and Joe Wessels

Control of corn earworm, Helicoverpa armigera, in maize has generally not been practised because of the high cost associated with repeated insecticide application required during silking. In most years it is a case of forsaking the top of every cob to larval damage

However, in some years, very high pest activity results in more severe cob damage, with larvae often tunnelling into the sides of cobs. In such cases grain samples may contain fungus-affected grains and mycotoxins, causing a downgrade in the quality of harvested grain.

What can you do to prevent these losses?

Over recent years Helicoverpa nucleopolyhedrovirus (NPV) has demonstrated its versatility for corn earworm management. One of the major developments has been the effective application of NPV through overhead irrigation, sometimes referred to as ‘chemigation’.

ViVUS Max is currently the only insecticide registered in Australia for application in overhead irrigation water in a wide range of crops.

By adding NPV to irrigation water, growers can artificially inoculate their crop with NPV and achieve a high level of control of helicoverpa larvae.

The main guidelines for NPV use still apply. These include:

• Good coverage is essential as the product needs to be ingested
• Use in the temperature range 25-35°C when larvae are actively feeding
• NPV is more effective against smaller larvae
• Preferably target larvae less than 7 mm in length, but under ideal conditions larvae up to 13 mm in length will be controlled
• Larvae can take up to 8 days to die
• Spray water pH should be neutral (pH 7.0)

There are additional key points to the successful use of NPV via overhead irrigation.

• Application in overhead irrigation water provides the maximum coverage achievable
• Introduce NPV to the irrigation water at the appropriate rate using chemigation equipment
• If the NPV is diluted in water prior to injection into the irrigation water, ensure that the dilution water is clean and not silty with a pH of 7 or less
• Ensure constant agitation in the premix tank
• Ensure any diluted NPV is used within 10 hours of mixing
• Apply in no more than 10 mm of irrigation water

• For one-pass mobile irrigators such as centre pivots, laterals and travellers (guns), continuously introduce the required amount of ViVUS Max into the irrigation water over the course of irrigation.

What rates to use? How often?

For ViVUS Max in maize, the registered rate for normal foliar application is 150 mL/ha. When applied in overhead irrigation water, reduced rate repeat applications have been used successfully. An effective prophylactic strategy would be to make the first application at full tassel emergence (50 to 150 mL/ha depending on larval numbers and size) and then low rate (50 to 75 mL/ha) applications every 5 days or so until late blister/early milk stage.  A total of 4 applications would use about 250 mL/ha (perhaps more under high pressure). This product cost is around $30/ha and will keep things very clean.  

What are the economics of losses to larvae?

A back of the matchbox calculation can be used to give some insight to the damage caused by larvae. An average plant population is 70,000 plants/ha with one cob per plant and one larva per cob. Assume one larva consumes 15 kernels in its lifetime (Note: this value has no validated scientific basis). With an average kernel weight of 4,000 kernels/kg, one larva consumes about 3.8 g. If maize is valued at $300/t, this loss amounts to 262 kg/ha or $79/ha. Based on these rough figures, and assuming a high level of control, there is likely to be an economic benefit from using NPV. Larvae damaging early silks can also reduce pollination, which can result in even greater yield reductions.

Other benefits

As NPV is safe to natural enemies, parasites and predators remain in the crop and keeps working in your favour. This is particularly relevant for the egg parasite Trichogramma which is sometimes very abundant in maize crops. Untreated maize crops can also generate large numbers of helicoverpa moths, so control of larvae in maize can reduce subsequent pressure in nearby crops.

Article by David Murray and Anthony Hawes.  Image of lateral move irrigator by Graham Harris.

  Mealybugs are small, sucking insects related to aphids. Female adults are around 3 mm long, oval-shaped and covered by a white waxy coating giving them a mealy appearance. Nymphs are smaller but similar in appearance. Males are small aphid-like winged insects.

Mealybugs have a high reproduction rate with female mealybugs capable of producing hundreds of nymphs. Development from egg to adults takes about 26 days and adults can live for about three months.

Damage symptoms

Mealybugs form colonies on shoots, stems, and leaves developing into dense, waxy, white masses. Both adults and nymphs pierce and suck on plant tissue and are able to suck sap from hard tissue, including the main stem and branches. They can affect any stage of crop development.

 Symptoms of mealybug infestations on cotton include; crinkled and twisted leaves, fewer flowers and fewer bolls, smaller bolls, and distorted and stunted plants. Boll opening may also be adversely affected, resulting in serious losses in yield.

Mealybugs, like aphids, excrete copious amounts of honeydew that contribute to the development of a black sooty mould which inhibits the plant’s ability to manufacture its food. Ants feed on the honeydew produced by mealybugs and help to spread the infestation. Ants also protect mealy bugs from predatory ladybird beetles, parasites and other natural enemies.

 Where are they found?

Mealybugs are present in all cotton growing regions of the world. However on the Indian subcontinent, the exotic Phenacoccus solenopsis has become a major pest, possibly due to favourable weather conditions and an abundance of host plants. It has been responsible for heavy losses in Pakistan where it is now considered a major pest of cotton.

A mealybug found in Australian cotton fields in the Burdekin region was identified as Phenacoccus parvus. This pest was introduced accidentally as a contaminant on imported plants in 1988. P. parvus was initially found in isolated populations from far north Queensland to central New South Wales, and around Perth. It is more common in the drier regions of northern New South Wales and southern Queensland and population numbers of P. parvus increase during dry periods. Heavy infestations have been reported on lantana in south east Queensland. The species of mealybug infesting cotton in the Emerald region is yet to be determined.

 Management of mealybugs

There are no registered insecticides for the control of mealybugs on cotton in Australia. In Pakistan numerous pesticides have been evaluated for the control this pest, but a hydrophobic (water repellant) layer around its body makes it difficult to control with insecticides. To achieve effective chemical control, an insecticide must penetrate the outer waxy layer. 

The adult mealybug can shelter in the soil, cracks and other places where insecticide sprays cannot reach it.

The insect damage often appears in patches within a field, along field margins and poorly drained areas.  Mealybugs have numerous weed and crop plants that they use as alternate hosts; cotton, lantana, leucaena and peanuts are just a few.

Control of weeds and ratoon cotton, and avoiding planting on poorly drained soil is the best management option for controlling mealybugs at present.

 More information about the mealybug problem in India and Pakistan can be found on the CRDC website at www.crdc.com.au. To find the article search for mealybugs at the top of the page. 

Other pests

We have received a few reports from other pests in various crops. These include; Rutherglen bugs in mungbeans, monolepta beetles on peanuts and legume web spinners on soybeans. Please let us know if you are finding these pests and we can feature an article on these, or others you find, in the next blog.

Article by Kate Charleston and David Murray. Images by Paul Grundy.

C. Mares (CSIRO)

Just when you thought things were going along pretty well, something else pops out of the woodwork to bring you back down to earth. Some cotton consultants and their grower clients are concerned about the high numbers of thrips in their young cotton seedlings. Are they are problem? Do we need to control them?

Essentially, unless seedling terminals are dying, the damage to leaves, which causes distortion and cupping, is largely cosmetic and in most cases will not compromise yield and maturity. Only extreme populations (70 thrips per plant) caused maturity delays in excess of 7 days. Cool weather can exacerbate thrips damage, while warmer weather will help plants grow away from damage quickly – hence risks are higher in cooler regions and much lower in warmer regions.

Thrips are also important predators of spider mites, feeding on mite eggs as a source of protein, so it is important to weigh their value as predators against potential risk of yield loss or delay.

Which thrips?
Species infesting seedling cotton are tobacco thrips, Thrips tabaci, the most common, and tomato thrips, Frankliniella schultzei. Adults thrips are small, cylindrical insects (<1.5 mm long) with two pairs of narrow wings fringed with long hairs. Thrips tabaci is usually a pale straw colour while F. schultzei is typically almost black. Larvae of both species (< l mm long) are yellow and wingless.

L. Wilson (CSIRO)

The western flower thrips (WFT), Frankiliniella occidentalis is a recent exotic invader also found in cotton regions. It is similar in appearance to F. schultzei but paler, making it easy to distinguish from F. schultzei but hard to distinguish from T. tabaci. WFT causes similar damage to cotton seedlings and also eats mite eggs. It is resistant to a range of insecticides, including many organophosphates and carbamates.

What are we finding?
Most thrips collected last week on cotton seedlings on the Darling Downs were T. tabaci, but low numbers of F. occidentalis were present. The numbers of thrips nymphs were very low, indicating effective control (see below). The presence of high populations of adult T. tabaci where either granular insecticides or seed dressing have been used suggests there are constant influxes of adult thrips moving in from cereals and weeds (see below).

Thrips Thresholds
Due to the capacity to recover from some damage, thresholds for thrips must include both pest abundance and damage levels – which should both be exceeded before control is warranted.

From planting to flowering     (1 flower per metre)
Adults and larvae per plant                10
and
Damage (reduction in leaf area)        80%  (leaves less than 1 cm in length)

Control
Seed dressings can reduce early damage but will degrade over 14 to 21 days post planting (indicted by the presence of thrips larvae). By then leaf area should be sufficient for above-ground applications of systemic insecticides to be effective if necessary. Systemic granular insecticides, applied at planting, provide longer control, but in some districts they are not necessary for thrips control due to low numbers or good growing conditions.

If using seed dressings or granular insecticides be aware that adult thrips will continue to be found in the crop as they move from cereals and weeds. These adults will feed and die, causing no damage. The best indicator of declining control is the presence of thrips larvae which indicates that the pesticide is no longer effective.

For more detailed information on thrips follow this link:

http://www.cottoncrc.org.au/content/Industry/Publications/PestsandBeneficials/CottonInsectPestandBeneficialGuide/Pestsbycommonname/Thrips.aspx

Rod Collins and Hugh Brier did some investigative work back in 1998. They reared a couple of larvae through to the adult moths and had them identified by ANIC.

Rod Collins made the following observations: “The damage was usually confined to a single tiller per plant at a relatively low incidence through fields. Infected tillers seemed to have flowered normally, but soon after flowering the stem upwards from the last node (and including the head) died and was white in colour with no grain in the head. From a distance, these symptoms appeared to be the same as those of crown rot. However, infected tillers were green and apparently healthy from the last node (including the flag leaf) down. On closer examination, a small entry hole about the size of a pinhead was evident usually at or just below the first node up from the base of the plant. In some cases an exit hole was noted just above the last node.”

“When the stem was split open, you could follow where the larva had been up until the last node, where it was often found feeding on the tip of the stem just above the last node. In some cases, the larva had chewed through the tip and continued to move upwards towards the head. It appeared that once the stem began to dry out, the larva would bore a hole in the stem and exit. Only one larva was found per stem in all the plants that I saw.”

It seems not much is known about this species. It is believed to be a native species, one of three in this genus found in Australia. Ephysteris promptella is recorded as a pest of sugarcane in Australia. Ephysteris silignitis occurs widely in Australia south to about 35 degrees south and is thought to be confined to Australia. It is in the wettest parts e.g. Brisbane and Mt Bellenden Ker and the driest. It is common at Alice Springs. It was suggested that it may feed on grasses but there was no evidence.

Being aware of their presence is one thing; whether to intervene is another.

In some late crops starting to turn, the presence of up to 12 small armyworm larvae per square metre need not necessarily sound alarm bells. This situation requires careful and regular monitoring, but there is every chance the crop will make it to harvest without the need to control armyworm.

If however, the crop lingers and the armyworm develop into medium and large larvae, there is a risk, particularly with barley, that head cutting will result in high yield losses. In this situation, quick action may be required to control armyworm and prevent losses.

The key points are
1) to be aware that armyworm are present and
2) to inspect regularly as the crop approaches maturity so that appropriate action can be taken if head cutting occurs.

For more information on armyworm, see the posting made on 20 October 2008.
Photo: Watch for the early signs of head cutting.

Reminder: Last date for Steward® EC use on chickpeas is 15 October

Winter pulses have had their expected share of helicoverpa infestations over recent weeks and most crops have been sprayed to control grubs. Strategies to minimise the risk of insecticide resistance are available. The following points should be observed.

Under the Insecticide Resistance Management Strategy (IRMS), the last use of Steward® EC for Central and Southern regions is 15 October, while the last use date for Northern (Central Queensland) regions (15 September) has long passed.

Grower and consultants are also reminded that for all pulse crops, not more than one application of Steward® EC per field is allowed for the crops entire growth cycle.

Access the full IRMS for 2009-10 on the Cotton CRC website:
http://www.cottoncrc.org.au/content/Industry/Publications/Pests_and_Beneficials/Insect_Resistance_Management.aspx