Avenge of the caterpillars…

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High rain­fall and active plant growth have cre­at­ed per­fect con­di­tions for insects to build up in high num­bers. On the Downs there have been reports of cas­tor oil loop­er and com­mon army­worm in plague num­bers as well as oth­er cater­pil­lars includ­ing sorghum head cater­pil­lar.

Be on the look­out for cater­pil­lar pests and use the guide below to help with iden­ti­fi­ca­tion. Cor­rect iden­ti­fi­ca­tion is impor­tant in man­age­ment and tim­ing of insec­ti­cide appli­ca­tion.

Com­mon Army­worm Leu­ca­nia con­vec­ta
Com­mon army­worm is gen­er­al­ly con­sid­ered a spring pest but heavy infes­ta­tions have been record­ed in oats in the Jondaryan area. At this time of year com­mon army­worm can defo­li­ate seedling crops and pas­ture when in high num­bers. In spring, as win­ter cere­als are matur­ing, infes­ta­tions of army­worm arise from large migra­tions of moths from inland Aus­tralia. Infes­ta­tions now do not mean that these fields or farms will nec­es­sar­i­ly get army­worm in spring.

Com­mon army­worm is a hair­less, striped cater­pil­lar with three bands imme­di­ate­ly behind the cater­pil­lar head. They are noc­tur­nal, hid­ing under plants dur­ing the day and are often observed curled up in a ‘C’ shape. Colour is not a use­ful iden­ti­fi­er for army­worm as it is high­ly vari­able depend­ing on diet and pop­u­la­tion lev­els, but the three white bands imme­di­ate­ly behind the head are always present.

Pupa of the wasp par­a­sitoid Cote­sia sp. are present in high num­bers and will be an impor­tant nat­ur­al ene­my for this pest.

Com­mon army­worm is noc­tur­nal so any insec­ti­cide should be applied at dusk/night.  Small (ear­ly instar) army­worms can be con­trolled with Bt which will also pre­serve nat­ur­al ene­mies but it is not effec­tive on large cater­pil­lars. Large cater­pil­lars can be treat­ed with a range of chem­i­cals includ­ing chlor­pyri­fos. Chem­i­cal options can be found on the APVMA web­site.

Be care­ful if treat­ing infest­ed pas­tures as there are long with­hold­ing peri­ods for cat­tle grazed on this pas­ture with ref­er­ence to export slaugh­ter inter­vals and export graz­ing inter­vals. These inter­vals are not always marked on insec­ti­cide labels.

The export slaugh­ter inter­val for chlor­pyri­fos is 42 days and the export graz­ing inter­val is 56 days. For  infor­ma­tion about slaugh­er and graz­ing inter­vals relat­ing to oth­er chem­i­cals, please con­tact us via the blog. 

Sorghum Head Cater­pil­lar Cryp­to­blabes ado­c­eta
Sorghum head cater­pil­lar has been report­ed in the Chin­chilla area in sorghum. Sorghum head cater­pil­lar is a grain feed­er with most severe dam­age occur­ring at the soft dough stage.

The most obvi­ous iden­ti­fi­er of sorghum head cater­pil­lar is web­bing in the grain. Cater­pil­lars are sim­i­lar in appear­ance to com­mon army­worm but small­er, reach­ing a max­i­mum size of about 13mm long. Sorghum head cater­pil­lar does not have the three white bands imme­di­ate­ly behind the head, and its body is tapered at both head and tail end.

Web­bing can make it dif­fi­cult to get good con­tact with the lar­vae when treat­ing infes­ta­tions with insec­ti­cide.

Cas­tor Oil Loop­er Achaea jana­ta
Cas­tor oil loop­er infes­ta­tions have been report­ed across the Downs https://thebeatsheet.com.au/general/castor-oil-looper-outbreak/ . Cas­tor oil loop­er is a pest of broadleaf crops like soy­bean although most out­breaks in the past few weeks have been in pas­tures where cater­pil­lars are feed­ing on broadleaf weeds like pig weed and marsh­mal­low weed.

Cas­tor oil loop­er is iden­ti­fi­able by a dark band run­ning across its back. It is high­ly vari­able in colour and may be stri­at­ed with var­i­ous colours includ­ing red, pink and black.

Insec­ti­ci­dal con­trol is best tar­get­ed at small grubs how­ev­er out­breaks of cas­tor oil loop­er are rel­a­tive­ly uncom­mon in crops. They could poten­tial­ly cre­ate a dilem­ma in pigeon pea refuges as Bt prod­ucts (e.g. Dipel) can not be used in a Boll­gard® cot­ton refuge.

Arti­cle by Zara Ludgate