Bug briefing: 30 June – 13 July 2020

 

Bug Briefing is an overview of some recent invertebrate reports sent to PestFacts south-eastern, providing a snapshot of pest and beneficial activity in broadacre crops and pastures in Victoria and southern NSW.

 

Pasture webworm

Pasture webworm (Hednota sp.) larvae were observed in Lismore in the Corangamite region of Victoria, causing heavy chewing damage to wheat in an area coming out of a pasture rotation.

In the Victorian Wimmera, pasture webworm larvae were discovered hiding in the soil next to young wheat plants that had been chewed down.

Pasture webworm larvae are also suspected to be responsible for chewing plants at the soil surface leaving behind bare patches in a paddock of wheat in North East Victoria.

Pasture webworm damage in Lismore. Image: Annieka Paridaen

 

Underground grass grub, pasture tunnel moth and ‘chubby armyworms’

Large numbers of underground grass grub (Oncopera fasciculatus) larvae have caused pasture damage on a property near Coleraine in the Glenelg-Hopkins region of Victoria.

They were found in a mixed population with Proteuxoa sanguinipuncta (also known as Peripyra sangunipuncta) larvae, a species that can look and behave similar to armyworm but is chubbier-looking and can be distinguished by a white diagonal stripes near its rear.

A patch of pasture tunnel moth (Philobota sp.) was also observed on the property.

While Proteuxoa sanguinipuncta and pasture tunnel moth larvae are known to feed on pasture, most of the damage has been attributed to the underground grass grub larvae.

An underground grass grub larva and a Proteuxoa sanguinipuncta larva. The red arrow shows the white diagonal line on Proteuxoa sangunipuncta, a feature not present on armyworms, which can look similar (left). Damage was largely caused by the underground grass grub (right). Images: Josh Brown

 

Pasture day moth

Pasture day moth (Apina callisto) larvae have again been spotted around young wheat, near Nhill in the Victorian Wimmera.

In one paddock, they were concentrated in a corner chewing on the young wheat but not causing much damage. A second paddock where they were spotted had quite heavy grazing damage, however on closer inspection, pasture webworm was found and is the likley culprit.

 

Armyworm

Native armyworm (Mythimna or Persectania spp.) larvae continue to be observed in cereals, with reports near Temora and Moama in NSW Riverina and also in Victoria near Lake Marmal and Echuca, North Central region, and Nhill in the Victorian Wimmera.

Population levels and larval sizes have varied, and not all populations have warranted control based on the with a monitoring and threshold approaches taken in some cases.

 

Brown pasture looper

Brown pasture looper (Ciampa arietaria) larvae continue to be spotted with varying degrees of impact.

They were present in a wheat paddock near Nhill in the Victorian Wimmera, however they were isolated to capeweed (their preferred host) and were not impacting the crop.

They were also reported in a cereal paddock near Wagga Wagga in the NSW Riverina, some grazing was evident, however the damage was not concerning.

High numbers of brown pasture looper were seen feeding on dryland lucerne near Bunnaloo, in the Murray region of NSW. They were found defoliating established plants but also feeding on younger seedlings, which were at risk of being killed.

Large brown pasture looper larvae were also observed in a lentil crop chewing on the leaves near Birchip in the Victorian Mallee. While brown pasture looper has been known to feed on several species of broadleaf plants (e.g. canola, lucerne, lupins), they are not commonly reported on lentils and it may not be a preferred host.

 

Flea beetle

The lesser or small striped flea beetle (Phyllotreta undulata) has again been spotted in a canola crop near Parkes, Central West NSW, and was the cause of some lucerne flea-like damage in some plants.

We reported on this flea beetle in June and had predicted that it may soon overwinter (become dormant) in the soil, leaf litter or stubble like it is known to do in some countries in the northern hemisphere. But as it has still been spotted one month into winter, it is likely that conditions don’t get cold enough in this region to cause overwintering.

It is important to note that Phyllotretta undulata is an introduced species that has been in Australia for well over a century and has not eventuated into a pest of canola (or brassicas) like in some northern hemisphere countries, and therefore the biology of this species in Australia has not been researched.

So far, the damage described doesn’t not seem as extensive as the damage experienced in the northern hemisphere where various flea beetle species are considered a major pest of canola.

If you have seen a seen this little black beetle with two yellow stripes (2 mm in length) in your canola, please contact us so that we can learn and share more about it.

The lesser striped flea beetle, aka the small striped flea beetle, Phyllotreta undulata. Image: laz (CC BY-NC-SA 4.0)

 

Weevils

Extremely high numbers of green weevil larvae were found devouring the foliage of marshmallow weed in Stockingbal in the NSW Riverina. The weevils were also present in the soil and the surrounding Phalaris and prairie grass pasture has been striped.

The prime suspect is the greybanded leaf weevil (Ethemaia sellata). There is not a lot know about this species, but we do know that they like to eat marshmallow above ground.

We received a sample of the weevil larvae but not all the features were consistent with greybanded leaf weevil so further investigation is needed, and we will keep you updated.

Getting to the bottom of this weevil’s identity is important as we previously wouldn’t have thought grey banded leaf weevil would damage grasses.

Green weevil larvae found defoliating marshmallow weed appear to be affecting surrounding grass pastures too. Images: Sandy Biddulph

 

Aphids

Russian wheat aphid (Diuraphis noxia) was reported on the majority of volunteer wheat plants in an oaten hay paddock in Wilkur in the Victorian Mallee. The oats were not being fed on by the aphids, most likely because oats are not a primary host of Russian wheat aphid, and they were also grown from insecticide-treated seed. In the same region a single plant with Russian wheat aphid was spotted in a wheat (no insecticide seed treatment) near Hopetoun.

We also received a single report of high green peach aphid (Myzus persicae) numbers in a patch of canola in the Victorian Mallee. Big bare patches were noted in the paddock with some of the plants hosting up to 150 – 200 aphids.

 

Acknowledgements

Thanks to the following for providing field observations: Annieka Paridaen (Premier Ag), Darcy Bullen (Western Ag), Sam Schulz (Elders), Josh Brown (McDonald Rural), Darren Jones (Crop Smart), Kris Dixon (Nutrien Ag), Daniel Andrews (Nutrien Ag), Mark Breust (Delta Ag), James Whiteley (AGT), Alistair Ferrier (Nutrien Ag), Clint Sheather (Nutrien Ag), Sandy Biddulph (Biddulph Rural Consulting), Craig Muir (Agrivision), Jayme Smith (Nutrien Ag), Greg Dearman.

 

Header image: Elia Pirtle, cesar