White-fringed weevil damaging field peas in Bundaberg

The white-fringed wee­vil (Nau­pactus leu­coloma) orig­i­nates from South Amer­ica and was first reported in NSW in 1932.  Although gen­er­ally asso­ci­ated with warm moist con­di­tions, this pest is now found in many crop­ping areas through­out Aus­tralia and they appear to be increas­ing their range. Infes­ta­tions often go unno­ticed until crops are planted and once they are estab­lished they are dif­fi­cult to eradicate.

White-fringe weevil larvae (10 mm) found under fieldpea crop in Bundaberg

White-fringe wee­vil lar­vae (10 mm) found under field­pea crop in Bundaberg

Large patches of dead plants in infested field peas

Large patches of dead plants in infested field peas

Dam­age

White-fringe wee­vils cause prob­lems in field crops as lar­vae that feed on lat­eral and tap­roots. They can cause major tap­root dam­age which may result in loss of vigour as well as plant death. Dam­age to plant roots can also leave plants sus­cep­ti­ble to root dis­eases. Adult wee­vils feed on leaves but cause lit­tle eco­nomic dam­age. Many pulse crops are sus­cep­ti­ble to dam­age espe­cially peanuts (they will also eat the pods), chick­peas, soy­beans and field peas. Other sus­cep­ti­ble crops include lucerne, cot­ton and maize. Crops are most sus­cep­ti­ble to dam­age dur­ing the seedling/early veg­e­ta­tive stages as their roots are smaller rel­a­tive to the size of the wee­vil lar­vae (12 mm when fully grown), and plants are more likely to be killed.

Dam­age symp­toms observed in field pea crop at Bund­aberg included wilted plants, dead plants and gaps in the plant stand. Closer inspec­tion of dam­aged plants revealed lar­vae had chewed through plant roots/stems just below or at ground level.

Iden­ti­fi­ca­tion and lifecycle

Lar­vae are leg­less, up to 12 mm long and 6 mm wide with slightly curved grey-white bod­ies. They have yellow-brown heads which are retracted into the body so only the jaws are vis­i­ble.  The adult wee­vil has a snout, is 12mm long with a grey-brown body and has a light stripe on each side of the wing cover. Their wing cov­ers are fused together and they can­not fly but can walk long dis­tances. They emerge from the soil in summer.

White-fringed weevil adult (12 mm)

White-fringed wee­vil adult (12 mm)

Sam­pling for white–fringed weevils

Before plant­ing, sam­ple soils to deter­mine pres­ence of wee­vils. Sam­pling should be done in autumn or win­ter when lar­vae are large and easy to find, and before the next sus­cep­ti­ble crop is planted. Using a spade, take a sam­ple of soil and sift soil to find grubs. Repeat sam­pling at 10 areas through­out the pad­dock. Most lar­vae can be found at a depth of 1-15cm.  If one of more grubs are found from 10 sam­pling sites, con­sider plant­ing a crop that is not sus­cep­ti­ble to this pest.

In young crops, look for leaf dam­age caused by the adult wee­vil. If sig­nif­i­cant leaf dam­age is evi­dent, look for adults at the base of plants. Note that in peanuts, this dam­age can also be caused by peanut scarab adults.

Man­age­ment of white-fringe weevils

Con­trol of white-fringe wee­vils with insec­ti­cides is dif­fi­cult. Plant­ing sus­cep­ti­ble crops in fields pre­vi­ously sown to legumes or other sus­cep­ti­ble hosts should be avoided. Estab­lished white-fringe wee­vil pop­u­la­tions can be reduced with long rota­tions of unsuit­able hosts such as cere­als and grasses.

White-fringed weevil larva and damage to peanut tap root

White-fringed wee­vil larva and dam­age to peanut tap root

Crop rota­tion sequences that have led to sig­nif­i­cant seedling death include chick­peas fol­low­ing peanuts in the South Bur­nett, peanuts fol­low­ing pota­toes on the Ather­ton Table­lands, mung­beans fol­low­ing lucerne in the Cal­lide Val­ley, and now also field peas fol­low­ing soy­beans at Bundaberg.

Images: Top two images by Simon Andreolli, BGA AgriS­er­vices Bund­aberg. Bot­tom two images by Joe Wes­sels, DAFF Kingaroy

Arti­cle by Kate Charleston and Hugh Brier

Posted in field peas, whitefringed weevil | Leave a comment

Aphids, virus and leaf feeding caterpillars in faba beans.

As the warm weather per­sists, insect activ­ity is remain­ing high. DAFFQ Ento­mol­ogy has received numer­ous reports of aphids, and leaf-feeding cater­pil­lars.
The aphids have been iden­ti­fied as cow­pea aphid and the cater­pil­lars as one of the summer-active army­worm species, Spodoptera exigua (lesser army­worm). The con­cerns about these are for the poten­tial for crop loss caused by direct feed­ing damage/defoliation or virus trans­mis­sion by the aphids.

Army­worm caterpillars

Large lesser armyworm larva (Spodoptera exigua) from faba beans. Photo: Chris Teague.

Large lesser army­worm larva (Spodoptera exigua) from faba beans. Photo: Chris Teague.

spodoptera_feeding_FB_CTeague

Spodoptera dam­age to faba beans — leaf feed­ing. Photo: Chris Teague.

The army­worm are leaf feed­ers, sim­i­lar to the clus­ter cater­pil­lar (S. litura) that attacks cot­ton, and the dayfeed­ing army­worm (S. exempta) that defo­li­ated late maize and sorghum crops in summer.

Although no work has been done directly on this species, or on the impact of defo­li­a­tion on faba bean, we can extrap­o­late from what we know about other defo­li­at­ing species to guide deci­sions. The reports from the Goondi­windi and Moree areas sug­gest that 2 to 3 lar­vae per plant are caus­ing less than 10% leaf loss on late veg­e­ta­tive faba bean plants. In soy­beans, the defo­li­a­tion thresh­old for heli­cov­erpa is 33%, a point beyond which the plant can­not com­pen­sate.
The army­worm will com­plete their devel­op­ment and pupate in the soil. The pupae will remain in the soil and emerge in spring. It is unknown whether they will re-infest the same faba bean crops, but it is more likely that the moths will dis­perse from these fields.

Cow­pea aphid

Shiny black adult cowpea aphid and grey-green juveniles.

Shiny black adult cow­pea aphid and grey-green juveniles.

Cow­pea aphid appears to be the dom­i­nant species in faba beans at present, although there may be a smaller num­ber of blue-green and pea aphid in the crops. The risk of crop dam­age caused by direct feed­ing of aphids is low, par­tic­u­larly as the pop­u­la­tions seem to be in decline in crops where they have been present for 2 to 3 weeks. In rapidly grow­ing crops it is unlikely that colonies of aphids will impair crop growth. In rarer instances, very heavy infes­ta­tions may occur that will slow crop growth and flow­er­ing. In autumn we expect to see high nat­ural enemy activ­ity with car­ry­over of the preda­tors (lady­bee­tles, hov­er­flies, lacewings, preda­tory bugs) and par­a­sitoid wasps from sum­mer crops. Where aphid pop­u­la­tions are in decline, there is clear evi­dence of par­a­sitism and predation.

Look for nat­ural ene­mies when you are check­ing aphid infes­ta­tions. Whilst nat­ural ene­mies won’t pre­vent virus trans­mis­sion, they will con­tribute to min­imis­ing aphid sur­vival and spread (and con­se­quently virus spread) within the field.

Aphid 'mummy'. Evidence of parasitoid wasps at work.

Aphid ‘mummy’. Evi­dence of par­a­sitoid wasps at work.

Hoverfly larva feeding on cotton aphid. This predator will feed on cowpea aphid too.

Hov­er­fly larva feed­ing on cot­ton aphid. This preda­tor will feed on cow­pea aphid too.

Cowpea aphid infestation in terminal of faba bean plant.

Cow­pea aphid infes­ta­tion in ter­mi­nal of faba bean plant.

Also take notice of the pat­tern of aphid infes­ta­tion in a field. Is it con­fined to the field mar­gins, or is it more wide­spread across the field, per­haps orig­i­nat­ing from broadleaf weeds that have hosted aphids in late sum­mer, early autumn? Be aware of pos­si­ble sources of aphids and viruses nearby e.g. weedy sum­mer crop, weedy fal­lows, lucerne. These fac­tors are rel­e­vant to virus risk and how you might most effec­tively imple­ment control.

As the weather cools, the aphid pop­u­la­tion growth will slow. Whether the aphid pop­u­la­tions die out com­pletely dur­ing win­ter, or sur­vive at low lev­els to build again in spring is unknown.

 Aphids as vec­tors of virus in faba beans

Bean leafroll virus (BLRV) and Bean yel­low mosaic virus (BYMV), Soy­bean dwarf virus (SbDV) and Sub­ter­ranean clover stunt virus (SCSV) are the most com­monly recorded viruses in faba beans. In the field, symp­toms of these viruses look very sim­i­lar and the only sure way to dis­tin­guish them is with anti­bod­ies or mol­e­c­u­lar tools. SCSV is not very com­mon, the only recorded inci­dence was a heavy infec­tion in 2003. How­ever, we might see it this year as its main vec­tor is cow­pea aphid. The main vec­tor for BLRV and SbDV is the pea aphid (but BLRV might also be trans­mit­ted by cow­pea aphid). BYMV is non-persistently trans­mit­ted and can there­fore be trans­mit­ted by a range of vectors.

All these viruses can cause sig­nif­i­cant yield losses if infec­tion occurs dur­ing the seedling stages and BLRV can still have a major impact with spring infections.

PBA Warda has higher level of tol­er­ance to BLRV than older vari­eties, but is not com­pletely resistant.

 

Subterranean clover stunt virus. Photo: Joop van Leur

Sub­ter­ranean clover stunt virus. Photo: Joop van Leur

Soybean dwarf virus. Photo: Joop van Leur

Soy­bean dwarf virus. Photo: Joop van Leur

Bean yellows mosaic virus. Photo: Joop van Leur

Bean yel­lows mosaic virus. Photo: Joop van Leur

Bean leafroll virus. Photo: Joop van Leur.

Bean leafroll virus. Photo: Joop van Leur.

It is impor­tant to remem­ber that not every aphid that lands in a faba bean crop is nec­es­sar­ily car­ry­ing virus. Virus symp­toms will appear in crops around 10 to14 days after infec­tion. BLRV symp­toms are upward rolling of leaves and inter­veinal yel­low­ing of older leaves. Symp­toms of BYMV are typ­i­cally vein yel­low­ing and green-yellow mosaic veins.

Once faba bean plants are infected with virus, they will remain infected. Plants infected in autumn become sources of virus in spring, although (depend­ing on the virus) the impact of the virus on yield will be lower if infec­tion occurs in a later stage of crop devel­op­ment. In-crop aphid man­age­ment becomes more impor­tant in pad­docks where autumn virus infec­tions have taken place.

Some regions are known to be high risk virus areas, e.g. Liv­er­pool Plains. Lit­tle is known about the rel­a­tive risk of virus in other regions.

Some fac­tors that increase virus risk in a region are: i) reg­u­lar rain­fall that pro­motes the growth of weed hosts on which the aphids can build up before mov­ing into crops; ii) weed or crop virus reser­voirs e.g. Lucerne, legume pas­ture, bras­sica weeds.

 

Man­age­ment of aphids
The con­ven­tional wis­dom is that if aphids can be read­ily seen in the crop, then they will have already trans­mit­ted virus (if they are going to) and there is no ben­e­fit in con­trol­ling them,  the dam­age is done. This sce­nario is prob­a­bly true in an autumn when the aphid infes­ta­tion is halted by cool weather. How­ever, with the extended period of mild weather this autumn, there is the poten­tial for aphids to colonise bean crops and then con­tinue to infest more widely in the crop. If these aphids are car­ry­ing virus, this sce­nario will result in more wide­spread virus infec­tion in the crop, with impli­ca­tions for yield and fur­ther infec­tion in spring.

The ben­e­fits of con­trol­ling aphids to pre­vent direct dam­age (feed­ing dam­age) is not well under­stood. The cur­rent think­ing is that the impact of direct feed­ing has lit­tle impact on yield, and is unwar­ranted unless aphid infes­ta­tions are extreme.

Thanks to Joop van Leur (NSW DPI) for infor­ma­tion on viruses and aphid vec­tors and pho­tographs of virus symptoms.

For more infor­ma­tion on man­ag­ing virus and other dis­eases in faba beans see the Pulse Aus­tralia web­site for the Dis­ease man­age­ment in faba beans fact­sheet and the Man­age­ment of pulse viruses fact­sheet.

Posted in aphids, armyworm, faba beans, pulses | Leave a comment

Whitefly in establishing canola crops — Central NSW

Over the past cou­ple of weeks there have been reports of white­fly adults infest­ing canola in the Cen­tral West and Lach­lan regions of NSW. This is not an occur­rence that has been recorded before, so we don’t know con­clu­sively what the out­come will be of these infes­ta­tions. What I have done is pulled together infor­ma­tion on white­fly that will help you make an assess­ment of what is hap­pen­ing in your crop, if you have a white­fly infes­ta­tion. Thanks to Richard Sequeira (Research Sci­en­tist, DAFF Queens­land) for his insights into white­fly behav­iour and poten­tial impact on crops.

Where are the white­fly com­ing from?

It is likely that the white­fly are Sil­ver­leaf White­fly, and are mov­ing out of cot­ton crops as they are defo­li­ated and picked. The warm sum­mer and autumn have allowed white­fly num­bers to build up in cot­ton crops this year. Large scale move­ment of white­fly from cot­ton was observed in Emer­ald dur­ing the early years of out­breaks. White­fly will fly some dis­tance them­selves, but can also be car­ried long dis­tances by wind. It is less likely that they are com­ing from weed hosts in these high densities.

What impact will the white­fly have on my canola (and pos­si­bly other broadleaf win­ter crops)?

We con­sider it highly unlikely that infes­ta­tions of adult white­fly will cause sig­nif­i­cant crop dam­age. We do not know how good a host canola is for white­fly, although hor­ti­cul­tural bras­si­cas (e.g. broc­coli) are good hosts. Regard­less of how good a host canola may be, con­sider the following:

1) White­fly is a warm weather species, and does not per­sist dur­ing cold weather. Even if day­time tem­per­a­tures are warm, the cool nights will slow the rate of feed­ing and repro­duc­tion; slow­ing the poten­tial impact on the crop.

2) Adult white­fly will live for 2 to 3 weeks under cooler autumn con­di­tions (no more than a week in summer).

3) Influxes of adults may con­tinue for some time, which will make it dif­fi­cult to deter­mine whether it is sur­vival or immi­gra­tion con­tribut­ing to the population.

4) The feed­ing done by juve­nile white­fly (nymphs) is far more dam­ag­ing to plants than adult feed­ing. If the white­fly are not repro­duc­ing, the poten­tial for crop dam­age is lower.

5) Eggs may be laid on plants that are unsuit­able for the sur­vival of nymphs. The pres­ence of eggs on canola, lupins, faba beans etc does not nec­es­sar­ily mean that the white­fly pop­u­la­tion is going to estab­lish in that crop.

What to look for to make an assess­ment of the dam­age poten­tial of a white­fly infes­ta­tion in win­ter crops.

1) Con­firm iden­tity of the white­fly. Use the images below to exam­ine adult and juve­nile white­fly and deter­mine if they are green­house or sil­ver­leaf. Green­house are sig­nif­i­cantly less dam­ag­ing than Silverleaf.

2) Is there evi­dence of feed­ing? Look for shiny, sticky speck­ling on lower leaves. This is hon­ey­dew that is secreted by both adults and nymphs as they feed on the plant. The more hon­ey­dew, the more feed­ing is going on.

3) Look for signs of crop stress: wilt­ing, red­den­ing in canola, retarded growth. Be real­is­tic about what may be being caused by the white­fly, and what may be mois­ture stress.

4) Look for the pres­ence of eggs and nymphs on the under­sides of leaves (see pic­tures below). A han­dlens or micro­scope will be nec­es­sary to see these on the leaves. Select the low­est leaves on the plants; those that have been exposed to the adult white­fly the longest.

Distinguishing Greenhouse and Silverleaf Whitefly nymphs and adults.

Dis­tin­guish­ing Green­house and Sil­ver­leaf White­fly nymphs and adults.

Silverleaf whitefly adult with eggs.

Sil­ver­leaf white­fly adult with eggs.

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Pod and Stem Boring pests of soybean – an update

The 2013/14 soy­bean grow­ing sea­son has been chal­leng­ing for many grow­ers with very low rain­fall and high tem­per­a­tures until late March. Crop stress was some­times wrongly attrib­uted to insect pests although a num­ber of crops were infested with more unusual pests such as etiella. The high tem­per­a­tures also increased the impact of lucerne crown borer in infested crops. Read More »

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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.

Read More »

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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

Read More »

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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. 

Dam­age:

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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