Grasshoppers are hatching
Recently there have been isolated reports of sand grasshoppers hatching in the Coorow area.
Last year the sand grasshopper caused feeding damage to crops and pastures at Coorow and on sandy soils across the West Midlands. This feeding damage combined with other contributing factors, such as a false break, over-grazing, or a low pasture seed bank, resulted in many pasture paddocks having low ground cover in 2021 despite the favourable seasonal conditions.
Widespread surveillance was conducted by DPIRD staff across the West Mildands area before the start of the 2022 growing season and this surveillance indicated that there were very low numbers of grasshoppers present.
Monitoring and management
Growers and consultants, particularly in the West Midlands region, are reminded to closely monitor paddocks for Common Urnisa grasshoppers, which are also known as sand grasshoppers.
Common Urnisa is usually mottled and is a reddish-brown colour or grey, depending on its habitat. The Common Urnisa lacks the 'x' on its thorax that can be seen on the APL. The hind legs of the Common Urnisa has two dark bands across it and is yellow to orange on the inside whereas the lower part of the leg (tibia) is a purple to red colour and the knees are almost black.
If crop or pasture loss is occurring due to grasshopper activity insecticides can be applied to control hatching nymphs. Nymphs are easier to control than adult grasshoppers. Insecticides registered for APL control will have efficacy on this grasshopper.
For more insecticide information refer to DPIRD’s Australian plague locust control: registered insecticides page and search for registered insecticides on the Australian Pesticides and Vetinerary Medicines Authority website.
If pasture paddocks have no grasshoppers but low seedling numbers, this is likely a sign of a low pasture seed bank. Research scientist Geoff Moore (DPIRD) recommends supplementary over-sowing of a cereal-pasture mix. Producers need to be proactive and have a plan in place to prevent wind erosion and maximise pasture productivity for the 2022 growing season.
More information on seasonal issues, including land and water management, can be found on DPIRD’s Season 2022 webpages.
For more information on Urnisa grasshoppers refer to;
- DPIRD’s Identifying and controlling Urnisa grasshopper or sand grasshopper page
- DPIRD’s Australian plague locusts and grasshoppers podcast
- West Midland’s Group Getting the jump on grasshoppers and locusts with Svetlana Micic podcast.
For more information contact Research scientist Svetlana Micic, Albany on +61 (0)8 9892 8591.
Article authors: Svetlana Micic (DPIRD Albany).
Aphid activity and turnip yellows virus detections
- South Stirling
Autumn and early winter is a crucial period of the growing season for early season green peach aphid (GPA) infestation and turnip yellows virus (TuYV) infection in canola.
As part of a DPIRD Boosting Grains Science Partnership surveillance project 88 yellow sticky traps were set up across 72 sites in the Albany and Esperance port zones from mid-March to mid-April.
Minimal aphid activity was detected. Low cabbage, green peach aphid (GPA) and turnip aphid numbers were caught at; Kendenup, South Stirling, Mobrup, Ongerup, Gnowangerup, Cranbrook, multiple sites around Gibson and Dalyup, plus Condingup
From these aphid populations TuYV was detected in GPA captured at Cranbrook, Kendenup and Mobrup.
DPIRD will continue to provide updates to growers and consultants throughout May and June as we collect data from our targeted sites in these regions.
The presence of volunteer canola and cruciferous weeds (particularly wild radish) in the grainbelt can give aphids a chance to build-up which can increase the risk of early incursion of TuYV if winged aphids transmit virus from infected weeds to vulnerable germinating canola crops.
Growers are urged to monitor their germinating canola for aphids and signs of symptomatic plants.
What is turnip yellows virus?
TuYV, formerly known as beet western yellows virus, is an obligate plant parasite transmitted by several aphid species that colonise canola including its principle vector, the GPA (Myzus persicae) and the minor vector, the cabbage aphid. For more information about these aphids refer to DPIRD’s Aphid management in canola crops page.
It causes yield and quality losses in canola crops. It also infects other crop and pasture species including mustard, chickpea, faba bean, field pea, lucerne, medic and subterranean clover.
Timing of infection is key with heavier losses more likely if infection occurs during the rosette phase of canola up until stem elongation (GS30).
TuYV systemically infects plants and cannot be sprayed-out post-infection like a fungal disease. Therefore, control of the virus needs to be focussed on prevention rather than cure.
Diagnosing and preventing turnip yellows virus
Signs of TuYV infection in the paddock include discoloured and stunted plants that occur in patches, in thinner crop areas or the edge of the paddock, and gradually spread.
TuYV infection causes reddening, purpling or yellowing of the lower leaves of canola plants. Plants infected early (well before flowering) are often pale and stunted and these plants produce few flowers or seeds. Symptoms are milder and stunting is lacking with late infection. Leaf symptom type and severity differ depending on plant age at infection, environmental conditions and the canola variety involved. Symptoms of TuYV in canola can be confused with those caused by nutrient deficiencies, waterlogging or other plant stresses that cause yellowing, reddening or purpling of lower leaves.
TuYV spread can be controlled by applying neonicotinoid seed dressings.
Foliar sprays can also be applied to reduce infected aphid numbers but GPA has evolved resistance to many insecticide chemicals. Effective chemicals currently available in Australia for control of GPA are alarmingly limited. Overreliance and misuse of one of the remaining insecticides, sulfoxaflor (Transform®), could be leading to reduced sensitivity in some Australian GPA populations. For more information see GRDC’s Aphid and insecticide resistance management in grain crops.
For more information on this work refer to DPIRD’s Turnip yellows virus early warning system page.
For insecticide recommendations, refer to DPIRD’s 2022 autumn winter insecticide guide.
Other management practices include; sowing into stubble and delayed sowing to avoid peak autumn aphid flights.
If you see aphids are colonising green bridge hosts, or you have symptomatic looking plants that you are concerned about, they can be tested for the presence of TuYV through the Department’s Diagnostic Laboratory Services – Pathology Services.
For more information refer to DPIRD’s Turnip yellows virus in canola: diagnosis and management page.
For further information contact Research scientist Benjamin Congdon, South Perth on +61 (0)8 9368 3499.
Article authors: Benjamin Congdon (DPIRD South Perth) and Cindy Webster (DPIRD Narrogin).
Downy mildew and damping off in canola
- Esperance district
Agronomists are finding downy mildew on canola in the very wet, early sown areas of the Esperance district, such as Scaddan and Coomalbidgup.
There is also some damping off occurring in canola in the wetter areas of the Esperance district.
Downy mildew symptoms
Canola downy mildew mainly affects young cotyledons, true leaves and expanded leaves, however the latter are usually less severely affected.
Symptoms of downy mildew typically appear as yellowed cotyledons and lower leaves. Older leaves display angular yellow lesions on the upper leaf surface. Sometimes the lesions appear as creamish, circular to irregular spots of varying sizes on the upper leaf surface that turn brownish over time.
Examination of the underside of these leaves often shows a corresponding patch of white fluffy growth, although this can become less apparent with age. Severely affected cotyledons shrivel up and senesce prematurely.
While some early seedling mortality may occur, canola plants usually overcome the disease once they reach the cabbage stage. Infected plants will exhibit slower growth earlier in the season due to a combination of cold weather and presence of disease. Plants grow away from disease as they get older and as the weather warms up during spring.
Disease is generally favoured by cool (15-18◦C) wet conditions coupled with high humidity. Under such conditions, disease spreads very rapidly.
Downy mildew is either soil borne, seed borne or requires a green bridge for carry over. Once the primary lesions are formed on the underside of the leaves, secondary spread of the disease occurs via the airborne spores formed in the primary lesions. Disease epidemics are sporadic, therefore developing control strategies against downy mildew can be very challenging.
Most of the current canola varieties are susceptible to downy mildew.
More information about this disease can be found at DPIRD’s Diagnosing downy mildew in canola page.
Damping off symptoms
Damping-off is seedling root and hypocotyl (seedling stem) disease that can be caused by a complex of Rhizoctonia, Fusarium and Pythium fungi.
The damping-off diseases are often first seen in early sown canola crops, which are emerging under warm and wet conditions. When the cold, wet weather arrives, post-emergence death of seedlings can occur. If poor seedling emergence (pre-emergence damping off) is seen after sowing it is often possible to re-seed the paddock without damping-off occurring later in the winter period.
The symptoms of damping-off diseases often occur in patches with the affected seedlings having an orange–red coloration, stunted appearance or poor root development, depending on the pathogen present.
More information about this disease can be found at DPIRD’s Diagnosing damping off in canola page.
Pythium and downy mildew are oomycetes, a special class of organism very different to regular fungi, which have a mobile zoospore that can move in water towards plants. Hence their preference for wet soil and the lack of efficacy of many common fungicides.
Pythium and downy mildew are both diseases that can be supressed with the seed dressing Metalaxyl but don’t generally respond well to anything else.
Post emergence suppression of downy mildew can sometimes be achieved with foliar applications of copper but this needs to be done prior to plant infection. Only one copper based fungicide (Cung Fu 350SC®) is registered for downy mildew in canola and needs to be applied as per product label. Previous research by Senior research scientist Ravjit Khangura (DPIRD) on fungicidal control of downy mildew has shown that foliar fungicides are usually effective against downy mildew if applied before the onset of the disease. The economic benefit is unlikely if sprayed after severe infection. Fungicide seed dressings containing metalaxyl (MaximXL®) may provide some protection against downy mildew if the disease pressure is low to moderate.
Both diseases survive for long periods in the soil and in paddocks where canola is regularly affected, prevention measures (seed dressing or preventative foliar applications) may be worthwhile. However, crops usually grow through downy mildew and pythium, which are not considered yield limiting. Where plant density is affected, Senior research scientist Mark Seymour (DPIRD) advises that 10-20 plants/m2 sown early is still better than more plants sown later.
For more fungicide information refer to DPIRD’s Registered foliar fungicides for canola in Western Australia page.
For more information on downy mildew or damping off in canola contact Research scientist Andrea Hills, Esperance on +61 (0)8 9083 1144 or Senior research scientist Ravjit Khangura, South Perth on +61 (0)8 9368 3374.
Article authors: Andrea Hills (DPIRD Esperance), Ravjit Khangura (DPIRD South Perth) and Cindy Webster (DPIRD Narrogin).
Nodorum blotch in wheat
Wheat seedlings from Esperance recently submitted to DPIRD’s Diagnostic Laboratory Services (DDLS) have been diagnosed with nodorum blotch (previously known as septoria nodorum blotch). The disease is caused by the fungus Parastagonospora nodorum. The plants were volunteer regrowth emerging through 2021 stubble following autumn rainfall.
Nodorum blotch is a stubble-borne disease, favoured by warm, wet weather, and severe damage can occur after heavy and frequent rain particularly in wheat-on-wheat situations. Infected regrowth poses a negligible risk to other crops in the region but does demonstrate that proximity to infected stubble is a key risk in the disease cycle.
Plant leaves infected with nodorum blotch have tan-brown oval or irregular shaped leaf blotches with yellow margins. Tiny brown fruiting bodies can occasionally be seen in lesions but are not easily visible to the naked eye. Badly affected leaves die back from the tip as blotches converge.
Lower leaves are affected on young plants.
Later in the season, nodorum blotch can spread to glumes (known as glume blotch) and stems, and heavy infection may cause blotching across the entire grain head with shrivelled grain at harvest causing yield and grain quality losses.
In WA, nodorum blotch often occurs in a disease complex with yellow spot on wheat. Yellow spot lesions more often start as yellow rather than tan, and fruiting bodies are not present in leaf lesions. It is very difficult though to distinguish yellow spot from nodorum blotch by visual leaf symptoms even for experienced plant pathologists who rely on lab diagnostic techniques to confirm which pathogen is present. Heads and glumes are not affected with yellow spot.
Leaf samples can be submitted to DDLS Plant pathology services for diagnosis of which pathogen is causing the symptoms. This can be worthwhile, particularly as symptoms may not actually be fungal. Leaf spot symptoms can sometimes be physiological, and these do not respond to fungicide application.
For more information refer to DPIRD’s Diagnosing septoria nodorum of wheat page.
Varieties differ in susceptibility to nodorum blotch.
Greatest yield response to fungicide application for nodorum blotch in wheat canopy is achieved through application at flag leaf emergence. However, earlier application (eg at first node, Z31) may be considered if a susceptible variety has been sown into wheat stubble or disease pressure is high early, particularly if there is yellow spot present. When the disease is seen moving up the leaf canopy after flag leaf emergence, infection of heads (glume blotch) is a risk and this can cause significant loss of yield and grain quality. Glume blotch is best prevented by application of a registered fungicide when the crop is at grain ear emergence (Z55 - 59).
Growers should prioritise disease management of wheat sown on wheat stubble, especially early sown susceptible wheat crops, as these are likely to be more vulnerable to developing disease, especially glume blotch, because they have heads exposed for longer.
YellowSpotWM is a free app available to assist with making economic fungicide spray decisions for managing yellow spot in wheat. Users can specify factors relating to paddock selection, variety, seasonal conditions, prices and management options so that the output relates to their cropping circumstance. For more information refer to DPIRD’s YellowSpotWM page.
More information on registered fungicides can be found at DPIRD’s Registered foliar fungicides for cereals in Western Australia page.
Further information about this disease can be found at the department’s Managing yellow spot and nodorum blotch in wheat page.
For more information on wheat diseases contact Plant Pathologists Andrea Hills, Esperance on +61 (0)8 9083 1144, Ciara Beard, Geraldton on +61 (0)8 9956 8504, Geoff Thomas, South Perth on +61 (0)8 9368 3262, or Kithsiri Jayasena, Albany on +61 (0)8 9892 8477 .
Article author: Ciara Beard (DPIRD Geraldton).
Article input: Geoff Thomas (DPIRD South Perth), Hossein Golzar (DPIRD South Perth), Jean Galloway (DPIRD Northam) and Manisha Shankar (DPIRD South Perth).
Plant disease webinar recording can now be viewed online
On Thursday, 28 April 2022 DPIRD Plant pathologists Geoff Thomas and Ciara Beard presented on a range of foliar disease topics to help WA growers and consultants prepare for the 2022 season.
- Findings of foliar disease surveillance activities in broadacre crops in 2021.
- The green bridge and foliar disease risk outlook for WA broadacre crops this season.
- Strategies for reducing sclerotinia risk.
The webinar recording is now available for viewing on the DPIRD YouTube channel. To view the presentation PowerPoint slides visit DPIRD’s About PestFacts WA page.
For more information on the webinar topics presented, contact Research scientists Ciara Beard, Geraldton on +61 (0)8 9956 8504 and Geoff Thomas, South Perth, on +61(0)8 9368 3262
Article author: Cindy Webster (DPIRD Narrogin).