sustainability through science & innovation

PestFacts Issue No. 6 - 29th July 2016

So you think you found armyworms?!

Sclerotinia stem rot of canola in 2016

More caterpillars

Symphilids - white millipede-like invertebrates hold back ryegrass pasture

So you think you found armyworms?! Armyworms are about…but so are ‘herringbone caterpillars’ and possibly other species. So how do you tell them apart?

Where have they been reported? For the second consecutive year, armyworm (Leucania convecta or Persectania sp.) damage in cereals has been reported in the Victorian Mallee and NSW Riverina near Swan Hill. In the same region Proteuxoa or ‘herringbone caterpillars’ have been chewing lentil, pea and chickpea crops. Also in the Mallee district, these caterpillars have been found in canola near Ouyen. However Proteuxoa activity has not been restricted to broadleaf crops. They have been found alongside larger populations of armyworm in a barley crop northeast of Birchip. In this case the paddock had a heavy stubble load and damage was mainly attributed to armyworm activity. Proteuxoa have also been observed in several wheat crops and a barley crop north of Manangatang. In the NSW lower western region near Lake Mungo, large numbers (>40/m2) have damaged wheat. Near Deniliquin in the NSW Riverina, considerable numbers (12/m2) of Proteuxoa in a barley crop were reported, alongside lower numbers of pasture day moth (Apina calisto). At this stage the damage is not severe enough to warrant control. Distinguishing common caterpillars in crops Armyworm are often confused with Proteuxoa, cutworms and native budworm. Most caterpillars found in crops are known as Noctuids. We have developed the following simple guide (based on generalisations) to help distinguish caterpillars in the Noctuid group. Below are some questions to ask yourself to help sort through these groups: Does it have 4 sets of (abdominal) prolegs (see Budworm image below to see 4 sets of abdominal prolegs)? If it has 4 sets, it will be an armyworm, budworm, cutworm or Proteuxoa. Loopers (for example, brown pasture looper) have 2 sets of abdominal prolegs. Is it hairy? Native budworm (and incidentally, pasture day moth) are distinctively hairier caterpillars than armyworm, Proteuxoa and cutworm. Budworms have noticeable hairs around the head region and all over its bumpy body, while other species have none or a few sparse short hairs. If it doesn’t have obvious hairs, does it have distinctive body stripes or other prominent markings? The giveaway feature of armyworm is the three parallel body stripes, always visible on the collar behind the head and usually continuing down the length of the body. While there are three species of armyworm commonly found in southern Australia, all three caterpillars have these distinguishing stripes. Proteuxoa sometimes have a central stripe, but also have a series of light diagonal slashes on each segment, resembling a herringbone or fishbone pattern. Hence their nickname, ‘herringbone caterpillars’. One common species of this group has a lighter patch on the final abdominal segment. And if it doesn’t have hairs, or distinctive body markings? Cutworms have no distinctive markings or obvious hairs and are often described as having a smooth greasy appearance.

Armyworm larvae with three parallel white stripes on the collar, back and sides (left) (Source: Copyright © Western Australian Agriculture Authority, 2015); Proteuxoa with distinct herringbone pattern on the back (right) (Source: cesar) Native budworm, with distinctive body bristles (left) and cutworm with no obvious hairs or stripes or herringbone markings (Source: cesar)

About 'herringbone caterpillars' There is little known about the biology of ‘herringbone caterpillars’ that are causing damage this season in the lower rainfall cropping regions; in fact there is not even a common name for the pest. There may be 70+ species in this genus. Like other Noctuid pests, it is likely this species breeds on native vegetation in inland areas.

It may be that the common pest that we have been observing this year and last is Proteuxoa atrisquamata, although the taxonomy is unclear. This species has a distinctively lighter final abdominal segment. The genus Proteuxoa is currently undergoing a major taxonomic revision and in time this will bring more clarity.

Caterpillars grow to approximately 35-40 mm in length and the rate of feeding damage will increase as the larvae progress towards maturity. Different species have been found attacking both cereal/grasses (Graminae) and broadleaf crops (pulses and oilseeds), although it is unlikely that any one species would cross over between groups, say from cereals to pulses.

Our advice Medium to large armyworms present in cereals at this time of year will not cause head lopping later in the season. Crops can tolerate a reasonable amount of defoliation. For winter outbreaks of armyworm during tillering, economic thresholds of 8-10/m2 provide a guide for spray decisions. While there are many insecticides registered against armyworm, we recommend they be used judiciously because of the risk of inducing secondary outbreaks of other pests. Parasitic flies and wasps, and predatory beetles and shield bugs commonly attack armyworms, and can suppress natural populations, particularly in spring, if not disrupted by broad-spectrum insecticides.

Of course, there are ‘softer’ insecticides such as Bacillus thuringiensis (Bt) available that would preserve beneficials. Spray Bt late in the day/evening to minimise UV breakdown of the product, and ensure the insecticide is sprayed out within 2 hours of mixing. Make sure the appropriate strain is used for the target pest, add a wetting agent and use high water volumes to ensure good coverage on leaf surfaces. There has been no research on the management of Proteuxoa in grains. However, we expect that healthy vegetative crops should outgrow moderate foliar loss, although regular monitoring is recommended. As with armyworms, when making control decisions, consider the number and size of larvae, the likely extent of damage remaining before pupation, and the ability of the crop to compensate.

If chemical intervention is warranted, alpha-cypermethrin has been reported to provide adequate levels of control.

Click here for information on armyworms.

Sources of field reports of armyworms and ‘herringbone caterpillars’

Luke Maher – Agronomist, AGRIvision Consultants (Victorian Mallee) Andrew McMahen – Agronomist, Landmark (Victorian Mallee) Johanna Morgan – Agronomist, Swan Hill Chemicals (Victorian Mallee) Craig Muir – Agronomist, AGRIvision Consultants (Victorian Mallee) Rick Rundell-Gordon – Senior consultant, all-AG Consulting and Tech Services (Victorian Mallee) Matt Tubb – Agronomist, Landmark (NSW Riverina)

Twitter sources:

Gavin Howley (@GavinHowley) Andrew Parr (@AndrewJParr1)

Sclerotinia stem rot of canola in 2016 Wet winter conditions have favoured the establishment of Sclerotinia stem rot in many southern farming districts

Article prepared by guest authors Dr Kurt Lindbeck and Audrey Leo (NSW DPI Wagga Wagga)

Sclerotinia stem rot is caused by the fungal pathogen Sclerotinia sclerotiorum. This fungus can infect over 300 plant species, mostly broadleaf plants, including many crop, pasture and weed species, including canola, lupins, chickpea, sunflower and lucerne. Levels of Sclerotinia stem rot have been increasing in recent years, particularly in southern NSW, with increases in canola plantings and wheat-canola rotations. Wet winter conditions in 2016 so far have been favourable for the disease to become established in many districts in the southern region.­­

How does Sclerotinia stem rot develop?

The disease cycle of Sclerotinia stem rot is complex compared with other plant diseases, which is why the disease tends to be sporadic in appearance between years and districts. For stem rot symptoms to develop a sequence of events has to occur:

Conditioning of the sclerotia in the soil Sclerotia are hard, black bodies that resemble rat droppings and are the resting stage of the fungus. They germinate in the soil to produce airborne fungal spores, which are released from small golf tee-shaped structures (5–10 mm in diameter) known as apothecia. For this to occur prolonged moist soil conditions are required. Soils have to be virtually saturated for 10-14 days for sclerotia to soften and germinate. Most sclerotia will remain viable and capable of producing apothecia for up to 3–4 years before survival slowly declines. Colonisation of petals or neighbouring canola

Spores of the Sclerotinia pathogen cannot infect canola leaves and stems directly. They require petals as a food source for spores to germinate and to colonise. When the infected petal eventually falls, it may become lodged onto a leaf, within a leaf axil or at branch junctions along the stem. If conditions are moist the fungus grows out of the petal and invades healthy plant tissue (either a leaf or stem), resulting in a stem lesion and production of further sclerotia within the stem, which will then be returned to the soil after harvest.

Sclerotia also have the ability to germinate in the soil, and produce branching, thread-like structures called mycelium, which directly infect canola plants in close proximity causing a basal stem infection.

Apothecia of the Sclerotinia fungus (left) and numerous sclerotia formed inside a canola stem with an advanced infection (right) (Source: Kurt Lindbeck)

Adequate moisture in the crop canopy

Weather conditions during flowering play a major role in determining the development of the disease. The presence of moisture during flowering and petal fall will determine if Sclerotinia stem rot develops. Dry conditions during this time can quickly prevent development of the disease, hence even if flower petals are infected, dry conditions during petal fall will prevent stem infection development.

Symptoms of Sclerotinia stem rot Symptoms of stem rot generally first appear in the crop 2-3 weeks after initial infection. However, it will take a further 2-3 weeks for dead plants and branches to appear within the crop.

At first lesions may appear on leaves before the stem rot develops.This is the consequence of infected petals falling onto lower leaves and leaf junctions when the crop canopy has adequate moisture. Leaf lesions are grey and will develop and spread from under a fallen petal.

Stem lesions first appear as discreet light brown discoloured patches on plant stems and branches, often originating at a leaf or stem junction. These lesions expand; take on a greyish white colour, giving the plant a bleached appearance. At first stem lesions develop on one side of the stem, but will expand with time to completely girdle the stem, resulting in premature death above the lesion.

Infected canola plants ripen earlier and stand out as bleached or greyish-coloured plants among green, healthy plants. The bleached stems tend to break and shred at the base. When an infected canola stem is split open, sclerotia can usually be found inside. In wet or humid weather, a white fungal growth that resembles cotton wool (mycelium) can also develop on the infected stems and sclerotia may develop in this white growth on the outside of the stem.

Leaf infection by the Sclerotinia fungus, note the grey lesion forming from behind the petals (left) and early development of stem rot, note fluffy white mycelial growth on the outside of the stem (right) (Source: Kurt Lindbeck)

Predicting an outbreak

• Spring rainfall. Epidemics of Sclerotinia stem rot generally occur in districts with reliable spring rainfall and long flowering periods for canola. • Frequency of Sclerotinia outbreaks. Use the past frequency of Sclerotinia stem rot outbreaks in the district as a guide to the likelihood of future outbreaks. Paddocks with a recent history of Sclerotinia are a good indicator of potential risk, as well as paddocks that are adjacent. Consider the frequency of canola in the paddock. Canola is a very good host for the disease and can quickly build up levels of soil-borne sclerotia. • Commencement of flowering. The commencement of flowering can determine the severity of a Sclerotinia outbreak. Spore release, petal infection and stem infection have a better chance of occurring when conditions are wet for extended periods, especially for more than 48 hours. Canola crops that flower earlier in winter, when conditions are cooler and wetter, are more prone to disease development.

Managing Sclerotinia stem rot

Epidemics of Sclerotinia stem rot generally occur in districts with reliable spring rainfall and long flowering periods for canola. Paddocks with a recent history of Sclerotinia are a good indicator of potential risk, as well as those paddocks that are adjacent. There are important cultural management options to consider before the use of tactical fungicide treatments:

• Sowing canola seed that is free of sclerotia. This applies to growers retaining seed on farm for sowing. Consider grading seed to remove sclerotia that would otherwise be sown with the seed and infect this season’s crop. • Separate this season’s canola crop away from last year’s canola stubbles. This not only works for Sclerotinia, but other diseases such as blackleg. • Rotate canola crops. Continual wheat-canola rotations are excellent for building up levels of viable sclerotia in the soil. A 12-month break from canola is not effective at reducing sclerotia survival. Consider other low risk crops such as cereals, field pea or faba bean. • Follow recommended sowing dates and rates for your district. Canola crops that flower early, with a bulky crop canopy are more prone to developing sclerotinia stem rot. Bulky crop canopies retain moisture and increase the likelihood of infection. Wider row spacings can also help by increasing airflow through the canopy to some degree until the canopy closes.

If the situation warrants it, consider the use of a foliar fungicide. Weigh up yield potential, disease risk and costs of fungicide application when deciding to apply a foliar fungicide.

Use of foliar fungicides

The opportunity to apply foliar fungicides to manage the disease is approaching. Ideal timing for foliar fungicides commences at the 20 – 30% bloom stage (15 – 20 open flowers off the main stem). At this stage a foliar fungicide application will target early flowers, but also allow penetration of the fungicide into the crop canopy where infected petals are likely to become lodged. Bloom is defined as the number of flowers on each plant, not the number of flowering plants within the crop. The main aim of a foliar fungicide application at this crop growth stage is to protect the primary stem from early infection, which will cause the most yield loss.

Foliar fungicides applied to manage Sclerotinia stem rot will provide approximately 3 weeks of protection, so a single fungicide application may not prevent some later infections developing.

As crops commence flowering monitor weather events closely. Foliar fungicides are best applied before an infection event. Currently registered fungicides to manage Sclerotinia include Prosaro® and various fungicides containing iprodione or procymidone.

Contacts

Dr. Kurt Lindbeck, Plant Pathologist, NSW DPI, Wagga Wagga [email protected] Audrey Leo, Plant Pathologist, NSW DPI, Wagga Wagga [email protected]

More caterpillars Pasture webworm and pasture day moth have been reported mostly in cereals

Where have they been reported? Pasture webworm (Hednota spp.) larvae have caused patchy damage across a 250 ha wheat paddock south of Ouyen in the Victorian Mallee. Patches of damage ranged from 9-36 m2, with the worst damage seen on heavier ground. Low numbers of pasture day moth (Apina Calisto) were also found in the paddock, however damage from this pest appeared to be relatively minor. Another minor population has also been reported alongside Proteuxoa in barley, north of Deniliquin in the NSW Riverina.

We have had reports of damage by pasture day moth in tillering wheat in the Murrayville region of the Victorian Wimmera. An infestation has also been reported in capeweed growing to the side of a vetch crop on sandy ground west of Elmore in Victoria’s Northern Country. In this case the caterpillars had encroached 2 meters into the edge of the vetch crop.

About pasture webworm and pasture day moth Pasture webworm larvae are usually light-dark brown in colour and may have a tinge of the green gut contents showing through. They are about 1 mm long when newly hatched and reach a maximum length of about 18 mm. They have a smooth body and shiny dark heads. Older larvae have darker raised patches on each segment. Most larvae observed in the field will be large enough to be identified by the presence of these darker raised patches. Pasture webworm damage is recognised by the presence of severed cereal plants or leaves that are spread at different angles in the crop. Sometimes leaves may protrude from silk-lined tunnels made at the base of the plants.

Pasture webworm (Source: cesar)

Pasture day moth (Source: cesar)

Pasture day moth larvae are visually striking especially when fully grown. They are dull dark brown with reddish-orange and yellow markings, and two distinctive yellow spots near the posterior end of the body. They are also noticeably hairy with prominent bristles and grow to 60 mm in length.

Pasture day moth larvae most commonly attack broadleaved weeds in pasture, such as erodium and capeweed. In recent years, damage to emerging cereal and pasture crops, canola, peas, sub-clover and phalaris grass has been reported. This typically occurs in paddocks where pasture day moth are present and broad-leafed weeds are dead or dying from a herbicide spray; the caterpillars will transfer off the dying host plants and onto nearby crop plants. Our advice

Spraying crops for pasture webworm is recommended when 10 plants per square metre are damaged. We recommend spot spraying when infestations are patchy. A buffer zone of 20 metres around the infestation should also be sprayed. Providing the leaves of the plant crown are green, spraying will allow quite badly affected crops to recover satisfactorily. Various synthetic pyrethroids and chlorpyrifos are registered for pasture webworm control in pastures and forage crops. Cultivation, summer fallowing and grazing can reduce the chance on damaging infestations during winter.

The benefit of controlling pasture day moth is questionable in most years.The last substantial outbreak was in 2007 where pasture day moth were reported across much of southern NSW, mostly attacking cereals and emerging pastures.

Sources of field reports of pasture webworm and pasture day moth

Chris Dunn – Agronomist, Landmark (Victorian Northern Country)

Andrew McMahen – Agronomist, Landmark (Victorian Mallee)

Simon Mock – Agronomist, Clovercrest Consulting (Victorian Wimmera)

Matt Tubb – Agronomist, Landmark (NSW Riverina)

Symphilids - white millipede-like invertebrates hold back ryegrass pasture For the third year in succession, these unusual invertebrates appear to be constraining plant establishment

Where have they been reported? Large numbers of small, white to cream ‘millipede-like’ invertebrates have been reported closely associated with patches of seedling failure in an establishing annual ryegrass pasture near Corryong in Victoria’s North East. Concerns were first raised due to the poor performance of ryegrass in large patches within the paddock, where symphilids were found just below the soil surface.

Symphilids on the root system of a wheat plant (Source: M. Golder) In 2015, symphilids were found attacking establishing clover/phalaris pastures near Corryong, and in 2014 we received reports of symphilids attacking cereal crops around Young and Cootamundra in the South West Slopes district of NSW. These were the first symphilid reports to the PestFacts Service. All reports of symphilids have been from within the 600-900 mm annual rainfall zone.

About Symphilids

Symphilids are not common pests in Australia and are more frequently associated with Australian horticulture than broadacre agriculture. Accounts from the US and New Zealand, where they are more common, suggest that symphilids are found mainly in moist, open-structured soils often containing plant/ crop debris. Detailed information can be found at the Vegetables Victoria website and Massey University - Guide to New Zealand Soil Invertebrates.

Symphilids are not insects; they belong to the ancient sub-phyllum Myriopoda (“thousand-legged") and are thus closely related to millipedes and centipedes. The garden symphilid (also known as Symphylan in the US) are small, white, soft-bodied ‘centipede-like’ invertebrates, 3-7 mm long with 12 pairs of legs and a pair of antennae. The notable antennae are long and many-jointed. The soft, white body is divided into 14 segments, 12 of which bear pairs of hook-like legs. All of the legs on one side move simultaneously, alternating with those on the opposite side, thus producing a twisting and turning motion. They are sensitive to light and become very active when exposed.

Most symphilids are thought to be omnivorous, feeding on decaying organic material, soil microorganisms and root systems of plants. Some species are predominantly herbivorous. Importantly, herbivorous symphilids feed on the root hairs of plants and can also tunnel into the roots and stems leading to stunting and plant loss. They are known to feed on sprouting seeds and underground stems of seedlings. Depending upon the extent of feeding, plants are weakened or killed.

Our advice

There is nothing known about control options for symphilids in Australian cropping and pastures. We drew the following recommendations from New Zealand literature.

To check for symphilids, turn over at least 10 shovels of soil. Sift the soil while looking for active symphilids. Some research suggests that an average of 1 symphilid per shovel of soil may warrant chemical treatment of the infested area before planting the next crop.

Mark off the infested area; the entire paddock need not be treated.

Numerous naturally occurring organisms prey on symphilids in the field including true centipedes, predatory mites, predacious ground beetles and various fungi; however, nothing is known about their ability to control symphilid populations.

Sources of field reports

Graham Martin – Agronomist, Agmate Rural (North East Victoria) > In this issue

So you think you found armyworms?!

Sclerotinia stem rot of canola in 2016

More caterpillars

Symphilids - white millipede-like invertebrates hold back ryegrass pasture

What is PestFacts? PestFacts is a free e-mail service designed to keep growers and farm advisers informed about invertebrate issues – and solutions – as they emerge during the winter growing season. The service has a focus on pests of broad-acre grain crops.

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