Get documents about "new - Cereal aphids
Document Sample
PAgE 1
CEREAL APHIDS
fACt SHEEt
JULY 2010
NORtHERN REgION
Aphid control in cereals can pay
In high-pressure seasons, cereal aphids can cause yield loss in winter cereals
in northern NSW and Queensland.
KEY POINtS
■ Aphids can be controlled in
three ways: natural enemies, pre-
sowing seed treatment and foliar
pesticide sprays in response to
infestation.
■ Aphids have the greatest impact on
moisture-stressed crops, with large
populations exacerbating the impact
of the lack of moisture.
■ Small or moderate aphid
populations have less impact
and can be controlled by natural
enemies, although speed of control
can be a problem.
PHOtO: NORtHERN gROWER ALLIANCE
■ As crops mature and come into
head, aphids tend to disappear.
■ Recent research indicates oat
aphids affect yield by reducing the
number of viable tillers.
■ Identifying the presence of aphids
and their natural predators before
making insecticide decisions is
important.
Heavy infestations of these sap-sucking aphids (oat aphids) cause the crop to turn yellow,
be stunted and generally appear unthrifty.
New research indicates there can Barley yellow dwarf virus (BYDV) BYDV infects all cereals and can have
be financial benefits from controlling a significant impact on wheat, oats and
Cereal aphids are vectors of BYDV, a barley. Even low populations of aphids
the three main species of aphids that
disease that attacks all cereal crops. can spread the virus.
threaten cereal crops in the northern
However, BYDV does not appear to
region. Oat aphid, corn aphid and rose-
have a major yield impact in northern In other regions, plants infected
grain aphid favour barley, but are found
NSW and Queensland but can be highly with BYDV have less above-ground
in all cereal crops.
detrimental to crop yield in other regions. biomass and a reduced root system,
Heavy infestations of these sap- resulting in smaller grain size and
sucking insects cause the crop to Oat aphids are known vectors of BYDV lower grain yield. Researchers in the
turn yellow, be stunted and generally and these aphids are found each year in northern region have found it difficult
appear unthrifty. All three aphids can crops in the northern region. However, to detect symptoms of BYDV by
damage crops by feeding on them and there has been little detection of BYDV visual inspection because the signs
in some instances by spreading barley in the northern region except in crops on are similar to those of heavy aphid
yellow dwarf virus. the Liverpool Plains of northern NSW. infestation or moisture stress.
Level 1, tourism House | 40 Blackall Street, Barton ACt 2600 | PO Box 5367, Kingston ACt 2604 | t. +61 2 6166 4500 | f. +61 2 6166 4599 | e. grdc@grdc.com.au | w. www.grdc.com.au
PAgE 2
Nasty little suckers
OAT APHID (Rhopalosiphum padi) CORN APHID (Rhopalosiphum maidis) ROSE-GRAIN APHID
Despite their name, oat aphids can be found While they are most likely to be found in (Metopolophium dirhodum)
on all cereals including wheat, barley and oats barley crops, corn aphids also occur in The rose-grain aphid tends to colonise
and in most years of high infestation are the wheat as well as sorghum and maize. More the leaves higher on the plant, making it
most abundant species. A vector of BYDV, the rectangular in shape than the oat aphid, easy to detect and identify. Adults are up
oat aphid colonises the lower portion of the adults are 2mm long and may have wings to 3mm long, and are a large, pale aphid
plant with infestations extending from around with legs and antennae that are typically dark with a dark stripe down the midline of the
the plant’s base, up on to the leaves and and a green-blue body, sometimes with a back. Clusters of juveniles are common
stems as the crop starts elongation. Mature waxy appearance. Colonies generally develop on leaves.
adults are about 2 millimetres long and may within the furled emerging leaves of tillers
have wings that are dark green and rounded and they can be difficult to see. Corn aphids
or pear shaped, while the juveniles are paler can be important vectors of BYDV, if arriving
and smaller. Both are characterised by a dark early in crops.
reddish patch on the tip of the abdomen.
A fourth species, rice root aphid (Rhopalosiphum rufiabdominalis) exists in the northern grain region, but does not cause as much damage to cereals.
Natural enemies the lifecycle of a cereal aphid the immature aphid nymphs have
several growth stages, moulting at
and parasites When winged cereal aphids fly into
crops from grass weeds, pasture
each stage into a larger individual.
Sometimes the delicate pale cast
of aphids grasses or other cereal crops,
colonies of aphids start to build-up
skins can be seen near colonies.
Predatory insects, such as hoverflies within the crop. In Australia, all aphids When host plants become unsuitable
and ladybirds together with parasitic in a cereal crop are females, able to or overcrowded, winged aphids,
wasps, will naturally control aphid give birth to live young without the called alataes, develop and migrate to
populations in cereals. Unfortunately, need to mate. other crops or plants.
there can be a lag as the parasite and
predator populations build up and
aphids will continue to cause damage.
Parasitic wasps such as Lysiphlebus
testaceipes are particularly important
in the north. these tiny wasps inject
eggs into aphids causing them to
become ‘mummies’.
If mummified aphids make up
greater than 10 per cent of the aphid
population, it is a sign that parasitic
wasps are active. this most likely
means that the majority of aphids have
been parasitised and the population is
likely to crash within two weeks.
Dimethoate and synthetic pyrethroids
are highly disruptive to natural
enemies. Applying these insecticides
early may result in later reinfestation
of the crop because small numbers
of surviving aphids are no longer Mummified corn aphids: natural predators can help control small populations of aphids. Both
aphids and predator numbers should be assessed before in-crop insecticides are applied.
controlled by natural enemies.
PAgE 3
Latest research in collaboration with I&I NSW and
the Queensland Department of
durum at 400mL/100kg seed (figure
2). Both contain 180g/L imidacloprid
Employment, Economic Development or 72mL/100kg seed.
In 2008, the Northern grower and Innovation (DEEDI) at Dalby,
Alliance (NgA) in association with Lundavra, Yallaroi, Bullarah, Cryon, ■ Emerge® at 240mL/100kg seed on
Industry & Investment NSW (I&I NSW) tamworth, Spring Ridge and all crops which contains 600g/L
conducted trials at four locations on gilgandra. these trials compared the imidacloprid or 144mL/100kg seed;
three barley varieties, assessing the impact of aphids on barley, bread and
impact and economics of managing wheat and durum.
aphids. three species of aphid were ■ later foliar applications of pirimicarb
found, with peak populations At all sites, three species of aphid in the form of Pirimor® applied when
between 70 and 110 aphids/tiller at occurred – oat, corn and rose-grain. the aphid population was at 10/tiller
all four sites. Net economic benefits Peak aphid populations varied from and rising.
from control averaged $33 per hectare less than one per tiller at Dalby to
to $37/ha from either an aphid active 45/tiller at Bullarah. At the Moree site Aphid impact on yield and
seed treatment (imidacloprid) or a the populations of all three species economics of control
well-timed foliar insecticide (pirimicarb were assessed weekly. Patterns of
or dimethoate). the rise and decline of each species ■ NgA trial results in 2009 suggested
were almost identical on the two aphids caused up to 10 per cent
Dimethoate sprays applied to ‘crown’ loss in head number compared with
colonising oat aphids did not provide barley varieties, indicating that the
growth patterns of the barley had little plots where aphids were controlled
significant levels of control, although with either seed treatments or foliar
there was a weak trend to reduced impact on its attractiveness to the
aphids (figure 1). insecticides. Oat aphids appeared
aphid counts. Sprays were effective to have the greatest impact on head
once these aphids moved from number.
In 2009, two rates of imidacloprid
below ground level into the lower
were included in all trials (figure 2).
canopy as the weather warmed up ■ Over two seasons, NgA found yield
All treatments had the equivalent
during August. increases averaged around 11 per
loading of a fungicide seed treatment:
cent in barley and durum, and 5 per
Aphid numbers were not influenced by triadimenol (Baytan®) in barley and
cent in wheat. However, economic
barley variety. tebuconazole (Raxil®) in wheat and
returns from controlling aphids in
durum.
In 2009, NgA conducted two intensive wheat were still worthwhile due to
trials at Moree and Edgeroi evaluating Key treatments in all 2009 trials were: higher grain prices.
a range of management options on the
barley varieties groutA and fitzroyA. In ■ Zorro® on barley at 400mL/100kg
addition, eight trials were conducted seed and Hombre® on wheat and
FIGURE 1 Aphid population FIGURE 2 Efficacy of imidacloprid FIGURE 3 Efficacy of pirimicarb
dynamics on untreated FitzroyA seed dressing rate on total aphid foliar sprays on total aphid
at Moree, 2009 population at Moree, 2009 population at Moree, 2009
Aphids per tiller Aphids per tiller Aphids per tiller
30 30 30
25 25 25
20 20 20
15 15 15
10 10 10
5 5 5
0 0 0
Jun Jul Jul Aug Sep Sep Oct Jun Jul Jul Aug Sep Sep Oct Jun Jul Jul Aug Sep Sep Oct
16 6 26 15 4 24 14 16 6 26 15 4 24 14 16 6 26 15 4 24 14
Three distinct peaks are evident with each Control – Baytan® fungicide, no effect on aphids. Sprays were aimed to control populations of
aphid species building up rapidly then declining. each species when they were building up and
Flag leaves opened in late August corresponding Control Zorro®/Hombre® Emerge® at around 10 aphids per tiller (see Figure 1).
with the decline in the corn aphid population. The spray targeting the oat aphid (T1) was
delayed until the aphids moved from below
Oat aphid Corn aphid ground into the lower canopy. Each plot
Rose-grain aphid received a single spray at one of the three
timings. Pirimor® treatments gave quick
knockdown of the targeted populations.
Control Pirimor T1
Pirimor T2 Pirimor T3
PAgE 4
from one year of trials in 2009 by the
Northern grower Alliance the following
Aphid monitoring population may be building quickly.
Shorten the rechecking interval.
financial analysis showed: in winter cereals It may be useful to rate the number
■ over all the trials, in a low aphid Start checking for aphids in July. of aphids above and below the flag
pressure season imidacloprid Oat aphids appear first and tend to leaf separately. Corn aphids sitting at
at the low rate gave a net colonise the crown or sub-crown of the top of plants will be more readily
economic benefit in 61 per cent of the plant before moving on to the contacted than oat aphids at the base
comparisons, with an average net lower stem in late winter/early spring. of plants. this will be particularly useful
gain of $15/ha; to check for aphids, pull up 10 to 20 for assessing how effective a spray
plants from across the field and inspect has been and determining if surviving
■ the higher imidacloprid rate at cost aphids are those that may have simply
the crown and lower stem for aphids
of approximately $11/ha, gave the not been contacted.
and natural enemies. In barley crops,
greatest net economic return, giving
also check for corn aphids inside the
a positive return in 74 per cent of take time to sit quietly in the paddock
unfurled leaf at the top of the tiller.
cases and an average benefit of to observe natural predators.
$36/ha;
If aphids are detected,
implement a structured to spray or not to spray
■ the net return for a pirimicarb
spray averaged $12/ha. A sampling strategy. factors to keep in mind when deciding
positive return on investment when to apply an in-crop insecticide
Sampling should occur away from the
was achieved in 60 per cent of spray are:
edge of the paddock. Aphid numbers
comparisons. tend to be higher around the margins ■ the presence and numbers of
because this is where infestations natural predators.
Should I consider controlling start. the rest of the area will be more
aphids from seeding this year? representative of the infestation in the ■ Heavy rain will reduce aphid
Based on trials reported here, majority of the paddock. populations by knocking or washing
evidence suggests there is a case the individuals off plants. It may be
Estimate aphid infestation on individual worth rechecking numbers after a
to use seed treatments in barley.
tillers rather than whole plants. It can be storm if you had scheduled a spray.
this is because in barley it was
difficult to determine where an individual
found the need to apply a foliar spray ■ Corn aphids are likely to disappear
plant starts and stops, and the number
later in the season was high in both naturally once the flag leaf has
of tillers per plant is variable.
years of the trial if a seed treatment unfurled as they become exposed
was not used. Check five tillers at six sites within to parasites and predators.
a paddock. If the majority have
NgA intends to conduct further trials ■ Pirimicarb is a soft option for cereal
10 or more aphids per tiller a
in 2010 to determine the consistency aphid control, but it does have a
foliar insecticide spray should be
of responses in wheat and durum. withholding period.
considered. Be aware that this is a
One of the challenges of electing to
working threshold.
use a prophylactic treatment such ■ Applying insecticide to oat aphids at
as a seed dressing is that aphids are If aphid numbers are close to the the base of the plant can be difficult
a sporadic pest and will not reach notional threshold and there are in a dense crop and with aerial
damaging levels every year. lots of juveniles (small nymphs), the application.
Useful resources:
■ Northern Grower Alliance – Lawrence Price 07 4639 5344 Email lawrie.price@nga.org.au
■ DEEDI – Dr Melina Miles 07 4688 1369 Email melina.miles@deedi.qld.gov.au
■ The Beat Sheet – Insect Pest Management for Australia’s Northern Grain Region www.thebeatsheet.com.au
■ Crop Insects: the Ute Guide – northern grain belt edition
Ground Cover Direct, freephone 1800 11 00 44, ww.grdc.com.au/bookshop
■ GRDC Pestlinks www.grdc.com.au/pestlinks
Disclaimer
www.coretext.com.au
Any recommendations, suggestions or opinions contained in this publication or arising by reason of any person using or relying on the information in this
do not necessarily represent the policy or views of the Grains Research and publication.
Development Corporation. No person should act on the basis of the contents of caUTiON: researcH ON UNreGisTereD PesTiciDe Use
this publication without first obtaining specific, independent professional advice.
Any research with unregistered pesticides or of unregistered products reported
The Corporation and contributors to this Fact Sheet may identify products by
in this document does not constitute a recommendation for that particular use by
proprietary or trade names to help readers identify particular types of products.
the authors or the authors’ organisations.
We do not endorse or recommend the products of any manufacturer referred to.
Other products may perform as well as or better than those specifically referred All pesticide applications must accord with the currently registered label for that
produced by
to. The GRDC will not be liable for any loss, damage, cost or expense incurred particular pesticide, crop, pest and region.
Acknowledgements: Lawrence Price, Northern Grower Alliance
