Armyworms defoliating sorghum, millet and corn on the Downs

On the Dar­ling Downs there have been a num­ber of reports of com­mon army­worm caus­ing sig­nif­i­cant defo­li­a­tion in sorghum, corn and mil­let. Jim­bour grower John Alexan­der treated a severely defo­li­ated sorghum crop two weeks ago. Mil­let and corn crops in the same area have also been affected. Although patchy, the out­breaks have the poten­tial to cause sig­nif­i­cant yield loss if the army­worm defo­li­ate before the crop has reached phys­i­o­log­i­cal maturity.

Recent tweet from the Downs showing extent of defoliation to late sorghum.

Recent tweet from the Downs show­ing extent of defo­li­a­tion to late sorghum.

At this time of year, high num­bers of com­mon army­worm and dayfeed­ing army­worm can defo­li­ate seedling crops, sum­mer crops that are still green as well as pas­ture. The com­mon army­worm is the same species of army­worm that causes dam­age to win­ter cere­als in spring, and the high num­bers now may be a car­ry­over from the out­break in north­ern NSW last spring. Out­breaks for dayfeed­ing army­worm have been recorded in crops and pas­ture in late March and April in pre­vi­ous years. The last major out­break of dayfeed­ing army­worm (Spodoptera exempta) was in 2003, and prior to that in the 1970s.  Dayfeed­ing army­worm will attack both crops and the grass com­po­nent of pas­ture. Con­trol of army­worm in pas­ture has to be under­taken with care­ful con­sid­er­a­tion for with­hold­ing peri­ods for stock, par­tic­u­larly export graz­ing and slaugh­ter inter­vals which gen­er­ally are not on the label.

armyworm group

Com­mon army­worm larvae

Dayfeeding armyworm_DAFF

Dayfeed­ing army­worm larva

Both the com­mon and dayfeed­ing army­worm lar­vae look sim­i­lar to Heli­cov­erpa lar­vae. Cor­rect iden­ti­fi­ca­tion is impor­tant because army­worm can­not be con­trolled with NPV, and heli­cov­erpa have resis­tance to syn­thetic pyrethroids (the two most com­monly used con­trol options for these species). For iden­ti­fi­ca­tion of com­mon army­worm refer to a pre­vi­ous beat sheet post­ing When dayfeed­ing army­worm lar­vae develop under crowded con­di­tions, as in out­breaks, the lar­vae have a dis­tinc­tive blue-black coloura­tion and are inclined to exces­sive move­ment. The name dayfeed­ing army­worm is because out­break pop­u­la­tions will move and feed dur­ing day­light hours. Typ­i­cally, army­worm are active at night, shel­ter­ing dur­ing the day in the crop canopy or under stub­ble on the soil surface.

 Army­worm out­breaks like these tend to last only 1–2 gen­er­a­tions as dis­ease, pre­da­tion and par­a­sitism have an impact on sur­vival. The threat to win­ter crops is expected to be low, but mon­i­tor­ing as the crops emerge, par­tic­u­larly in prox­im­ity to army­worm out­breaks now, is recommended.

Con­sid­er­a­tions in the event of army­worm outbreaks:

Size of the lar­vae. Eighty per­cent of feed­ing is done by medium to large lar­vae. If the army­worms are longer than 30 to 35mm, they have com­pleted most of their feed­ing and the dam­age is already done. Treat­ing at this stage may be of lit­tle ben­e­fit. To be effec­tive, pop­u­la­tions need to be detected and con­trolled before large lar­vae have caused sig­nif­i­cant defoliation.

Thresh­old? Spe­cific thresh­olds have not been estab­lished for defo­li­at­ing army­worm in sorghum or corn in Aus­tralia. US data sug­gests con­trol­ling army­worm when crops have more than 50% defoliation.

Tim­ing of con­trol. With the com­mon army­worm, small lar­vae may feed dur­ing the day, but large army­worm feed at night and shel­ter on the ground under stub­ble and soil dur­ing the day. Apply­ing a treat­ment later in the day max­i­mizes the like­li­hood of con­tact­ing large, dam­ag­ing lar­vae as they climb the plants to feed. Con­trol options can be found on Con­trol of dayfeed­ing army­worm is straightforward.

Good cov­er­age is required to get con­tact with the cater­pil­lars, par­tic­u­larly in crops with thick canopies.
If treat­ing pas­tures beware of the 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.

armyworm and frass

army­worm and the dis­tinc­tive green/straw coloured droppings

Nat­ural ene­mies
Around 20 species of preda­tor and par­a­sitoids have been recorded attack­ing army­worm, but they are unlikely to pre­vent dam­age in an out­break sit­u­a­tion like those being reported.
The most fre­quently observed preda­tors are preda­tory shield bugs, lady­bee­tles, cara­bid bee­tles, lacewings and com­mon brown earwigs.

Par­a­sitoids include tach­nid flies and a num­ber of wasp species (e.g. Netelia, Lis­sopim­pla, Cam­po­letis).

Viral and fun­gal dis­eases can also cause mor­tal­ity of army­worm. Such out­breaks are more com­mon at high army­worm densities.

Click onto images to enlarge

Arti­cle by Kate Charleston and Melina Miles


Posted in armyworm | 1 Comment

New pest management website

Over the past few years the Queens­land DAFF ento­mol­ogy team has led a team of national col­lab­o­ra­tors to develop an excit­ing new national ‘IPM guide­lines for grains’ website.

The web­site focuses on the major grain crops and their pests, and includes a range of sup­port­ing infor­ma­tion to guide users in mak­ing pest man­age­ment deci­sions. Read More »

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Hugh Brier awarded GRDC’s Seed of Light, Northern Region.

Hugh Brier with his Seed of Light

DAFF Queens­land Ento­mol­o­gist, Hugh Brier, is the 2014  North­ern region recip­i­ent of GRDC’s Seed of Light.

The Seed of Light is pre­sented each year to some­one who makes a sig­nif­i­cant con­tri­bu­tion to com­mu­ni­cat­ing the out­comes of research. Read More »

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POSTPONED –Integrated pest management workshops in northern NSW

Please note: these work­shops have been post­poned to a later date

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Etiella on the move again

Back­ground: Sig­nif­i­cant etiella out­breaks have recently been reported in soy­beans and mung­beans on the Dar­ling Downs, in the South Bur­nett (SE Qld) and in the Moree and North­ern­Rivers regions of NSW. In some soy­bean crops on the Downs, 100% of plants were infested and 72% of axil­liary buds dam­aged to vary­ing degrees. These out­breaks are sim­i­lar but more wide­spread than etiella out­breaks reported in Jan­u­ary 2013. Etiella dam­age in soy­beans and mung­beans is gen­er­ally asso­ci­ated with pod­ding crops but the recent out­breaks show infes­ta­tions in veg­e­ta­tive and flow­er­ing soy­beans and budding/flowering mungbeans.

At this stage it is not clear why these out­breaks occur. One rea­son may be the very hot dry sea­sonal con­di­tions which favour etiella. It should be noted that the Jan­u­ary 2013 out­break ‘crashed’ with the onset of the wet sea­son due to cyclone Oswald. It is also pos­si­ble that the pest is adapt­ing to a new food source in dif­fi­cult seasons. 


Etiella damage to soybeans

Etiella dam­age to soybeans

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Downs update – Symphyla and other soil pests

Fol­low­ing the recent detec­tion of sym­phyla in some cot­ton fields on the Dar­ling Downs, DAFF Ento­mol­ogy have been test­ing sam­pling strate­gies for this poten­tial pest of cotton.

Lit­er­a­ture for a sim­i­lar sym­phyla species in North Amer­ica sug­gested that bait­ing with pota­toes may be an effec­tive strat­egy for assess­ing sym­phyla abun­dance and whether indi­vid­u­als were actively feed­ing or in a restive non-feeding devel­op­men­tal phase. Read More »

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Plant-based and dynamic thresholds for mirids in early stage cotton.

There have been a num­ber of reports of mirid infes­ta­tion in cot­ton on the Cen­tral High­lands and at St George. Recent research has focused on the devel­op­ment of plant-based thresh­olds that should make it eas­ier to make deci­sions about mirid control.

Typical mirid damage to a cotton seedling. Wilting and browning of terminal.

Typ­i­cal mirid dam­age to a cot­ton seedling. Wilt­ing and brown­ing of terminal.

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Symphylans recently detected causing establishment problems in cotton on the Darling Downs

An inves­ti­ga­tion into poor estab­lish­ment in a field of cot­ton west of Dalby this week con­firmed the pres­ence of the soil dwelling sym­phyla as the likely cause.

Sym­phy­lans are rel­a­tively com­mon in most soils where they gen­er­ally feed on decom­pos­ing organic matter.

Sym­phyla as crop pests

Sym­phyla have caused prob­lems with crop estab­lish­ment for a num­ber of sea­sons in the Theodore irri­ga­tion dis­trict and more recently in fields west of Moree.  Sym­phy­lans were first detected in Theodore in 2008/09 when prob­lems with patchy estab­lish­ment were clearly vis­i­ble across large areas. Inves­ti­ga­tions at the time by Dr Dave Mur­ray con­firmed the pres­ence of symphylans.

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Rutherglen bug in canola stubble – potential to damage establishing summer crops.

Canola stems with adult and nymphs clustered on the base after harvest.

Mul­ti­ple stems with adult and nymphs clus­tered on base post harvest.

Ruther­glen bug (RGB) are best known for the dam­age they can cause in sun­flower and sorghum dur­ing grain­fill, but they can also dam­age and even kill seedlings when present in large numbers.

In 2012 RGB dam­aged estab­lish­ing spring crops in areas of south­ern and north­ern NSW.

This spring, in some crops there are large num­bers of RGB in the canola stub­ble post-harvest.

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Spring pests of winter cereals

Army­worm in bar­ley and wheat.

A num­ber of reports of army­worm in crops have been received over the past cou­ple of weeks. Num­bers range from 30 to 50 per square metre (extreme) to a more typ­i­cal 5 to10 lar­vae per square metre.

Assess­ing lar­val den­sity is done using a sweep net, bucket or beat­ing a sec­tion of row into a tray or onto a beat­sheet. It is impor­tant to check along the row at the base of the plants for lar­vae shel­ter­ing in the soil and stub­ble. Army­worm are active at night, and tend to shel­ter on the ground dur­ing the day. At higher den­si­ties they may be active dur­ing the day. Read More »

Posted in aphids, armyworm, barley, blue oat mite, economic thresholds, wheat, Winter cereals | Leave a comment
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