WithTheGrain: Insecticide Resistance Management Strategies important for pest management

Author: | Date: 17 Aug 2018

Southern region growers are being encouraged to refer to insecticide resistance management strategies when managing pests such as redlegged earth mite (RLEM) this season.

cesar entomologist Dr Paul Umina emphasises the importance of active and informed decision-making through the use of resistance management strategies for key crop pests including RLEM, green peach aphid (GPA) and diamondback moth (DBM).

The need for resistance management strategies has been highlighted by recently confirmed resistance in multiple RLEM populations from South Australia to both synthetic pyrethroids (SPs), including bifenthrin and alpha-cypermethrin, and organophosphates (OPs), including omethoate and chlorpyrifos.

Red legged earthmite
The Redlegged earth mite resistance management strategy has been updated and growers are encouraged to seek out the resource when managing the pest this season.

Resistance management strategies are founded on the principles of reducing pest pressures through integrated pest management (IPM) including carefully considered application of insecticides. A key element of effective resistance management is the use of alternations, rotations, or sequences of different insecticide Mode of Action (MoA) groups.

An updated RLEM resistance management strategy has resulted from merging western and southern cropping region strategies into a national document following the discovery of resistance in the GRDC southern cropping region, with this strategy work being undertaken by the National Insecticide Resistance Management (NIRM) working group. The new strategy, which is now available on the GRDC website, has been redeveloped for growers and advisers across Australia and considers alternate management plans based on the presence of OP and SP resistance. It also provides a management plan for preventing the development of resistance for areas such as southern New South Wales and Victoria, which have no known resistance issues in RLEM.

Dr Umina says insecticide resistance in RLEM is still relatively new to south eastern Australia, and needs to be managed carefully to prevent it from becoming a widespread issue. The updated RLEM strategy shows that pest management strategies with a strong preference to spray insecticides rather than incorporate alternative IPM tactics, will perpetuate resistance problems.

“As anticipated, RLEM resistance is appearing at more localities and growers need to be aware of how to best manage mites to prevent this issue worsening and reduce the impact on crops,” he says.

“This season, RLEM have been more damaging than previous years in some localities in the south, in part driven by crops being slow to emerge given the seasonal conditions with dry and cold conditions hampering crop growth.

“This has resulted in crops being at a more vulnerable growth stage when RLEM populations are increasing in numbers after hatching.”

Recommendations for RLEM control (Table 1) include considering the impact of spraying on target and non-target pests and beneficial invertebrates and correctly identifying the mite species before spraying. IPM strategies involve year-round practices such as pasture management, maintaining clean fencelines and considering higher seed rates as methods to control RLEM populations.

Table 1: IPM strategies for the redlegged earth mite.
SeasonManagement optionComment
Previous year (winter/spring)Keep pastures short in early springIdeally graze to <1.4t/ha food on offer 3-4 weeks prior to the Timerite® date1. Heavily grazed spring paddocks will not require an insecticide spray.
 Keep fencelines cleanSpray out broadleaf weeds (especially in capeweed) along fencelines of paddocks that contain RLEM.
 Use selective chemicalsWhere possible avoid using organophosphates (OPs) or synthetic pyrethroids (SPs) for control of spring pests other than RLEM. For examples, use primicarb for control of aphids and Bt, NPV, spinetoram or emamectin benzoate for control of caterpillars.
 Use mite-tolerant pasture speciesFor continuing pastures, consider selecting varieties with known mite tolerance. The pasture legume Trifolium glanduliferum (cv Prima gland clover) is less susceptible to RLEM feeding. Subterranean clovers – NarrikupA, BindoonA and RosabrookA – may suffer less damage from RLEM than other varieties.
 Use mite-tolerant cropsIn situations where significant resistance issues exist, consider selecting crop types that are less susceptible to RLEM. Cereals are more tolerant than canola, and are typically better at compensating for early RLEM feeding damage. Some pulse crops, such as lentils and chickpeas, are not favoured by RLEM.
Pre-sowingControl weeds 2 weeks before sowingControl all weeds (especially capeweed and Paterson’s curse) using herbicides or cultivation within paddocks and along fencelines at least 2 weeks in advance of intended sowing date. This is especially important in ‘late break’ years where mites have hatched and are feeding on pre-sowing weeds.
 Avoid bare-earth sprays prior to mite hatchDo not apply preventative insecticides against RLEM in seasons where crops are sown in advance of known mite-hatching events.
 Use higher seed ratesConsider higher seeding rates to allow for some mite feeding damage and plant loss (especially in canola).
Emergence and crop establishmentMonitor and use spray thresholdsMonitor susceptible crops through to establishment using direct visual searches, and use thresholds to inform spray decisions. Avoid preventative or prophylactic insurance sprays.
 Use barrier sprays if mites invade from edgesBe aware of edge effects; mites move in from weeds around paddock edges. Where RLEM are colonising crop margins and fencelines in the early stages of population development, consider a barrier spray with an insecticide to prevent/delay the build-up of RLEM and to retain beneficial species.

1 Timerite® is a carefully timed chemical application in spring. This approach can drastically reduce the number of ‘over-summering’ diapause eggs produced by RLEM. If applied correctly, Timerite® will decrease the density of mites that emerge the following autumn. Further information is available at: www.wool.com/timerite

Implementing IPM strategies focused on spraying only when necessary and preserving beneficials is also advised for control of GPA and DBM, which together with RLEM, are the three key species with resistance concerns in the southern region.

GPA is widespread across the southern region affecting canola and a range of pulse crops through feeding and transmission of viruses. Young vegetative canola is most susceptible to GPA in autumn, while more mature canola late in the season does not often suffer yield losses due to the presence of GPA.

As use of chemicals to control GPA has increased, the selection pressure on the development of resistance has also increased. There is confirmed resistance to four insecticide groups: carbamates, SPs, OPs and neonicotinoids.

As a result, resistance management is important for GPA (table 2) and decisions can be made around crop type, location and population size as GPA presents as a cyclical outbreak pest rather than an annual one.

Table 2: Grains resistance management strategy for the green peach aphid across Australia.
Crop type and locationPre-emergence and establishmentPost establishment/pre-floweringRationale
Canola >50km from commercial horticultural regionsImidacloprid (4A) or Lambda cyhalothrin + thiamethoxam (3A + 4A)Paraffinic oilCarbamate (e.g. pirimicarb) resistance is commonplace. Its use is not recommended.
Canola <50km from commercial horticultural regionsSulfoxaflor (4C)Paraffinic oil*Carbamate (e.g. pirimicarb) resistance is commonplace. Its use is not recommended. Neonicotinoid (e.g. imidacloprid, thaimethoxam) resistance is probably emerging in horticultural crops. Its use is not recommended.
Pulses >50km from commercial horticultural regionsImidacloprid (4A)Dimethoate/omethoate1 (1B) or paraffinic oil (Note: apply a single treatment of 1B only, do not use repeated applications. Efficacy of 1B may be reduced if insecticides have been applied previously)Carbamate (e.g. pirimicarb) resistance is commonplace. Its use is not recommended. Organophosphate (e.g. dimethoate, omethoate) resistance is due to amplified E4 esterase, which is caused by prior exposure to organophosphates.
Pulses <50km from commercial horticultural regions*Dimethoate/omethoate1 (1B) or paraffinic oil (Note: apply a single treatment of 1B only, do not use repeated applications. Efficacy of 1B may be reduced if insecticides have been applied previously)Carbamate (e.g. pirimicarb) resistance is commonplace. Its use is not recommended. Organophosphate (e.g. dimethoate, omethoate) resistance is due to amplified E4 esterase, which is caused by prior exposure to organophosphates. Neonicotinoid (e.g. imidacloprid, thiamethoxam) resistance is probably emerging in horticultural crops. Its use is not recommended.
All crops and areasBiological control – improved prediction of aphid outbreak years to inform spray decisions High risk of GPA outbreak exists when summer rainfall creates a ‘green bridge’. Warm conditions in autumn favour early aphid build-up and flights into crops. In low risk years, the prophylactic use of insecticides, such as seed treatments, can be avoided.
All crops and areas Biological control – do not spray for GPA during or post floweringGPA infestations after the stem elongation stage rarely cause economic yield loss in high or medium rainfall areas of the southern and western regions (with the exception of their role as vectors of virus). In lower rainfall areas or under drought conditions, yield losses can result from the combination of moisture stress and aphid damage.
All crops and areasCultural control –avoid sowing into paddocks with bare ground; retain stubble where possible. Aphids are more attracted to a light open stand with bare earth visible between crop rows.
All crops and areas, except those in commercial horticultural regions and summer irrigationCultural control – control brassica weeds and volunteers (ideally area wide) no later than 3-4 weeks before sowing GPA persist between growing seasons on summer and autumn weeds, particularly wild radish, wild turnip, capeweed, volunteer canola and lupins. Removing the ‘green bridge’ will reduce aphid population sizes at the beginning of the cropping season. There is likely to be a suitable ‘green bridge’ for GPA all year in the majority of horticultural and summer irrigation regions, thus there is little that can be done about weeds.
1 N.B. Due to a recent review, omethoate is only registered for lupins in Western Australia for suppression only.

DBM also presents concerns for canola growers in the south. While canola can tolerate some leaf damage, severe infestations of DBM where the entire plant is affected can cause up to 80 percent yield losses.

Similar to GPA, strong selection pressure exists for chemical controls of DBM as chemical use continues to grow. Resistance management for DBM (table 3) centres on avermectins, spinosyns and biopesticide use, steering growers away from SPs and OPs where resistance is known to exist.

Diamond back moth
Resistance management for diamondback moth is required to ensure insecticide resistance levels do not increase.

Dr Umina says management tactics for all three pests remains much the same. Current advice centres on forward planning to implement an IPM strategy and making use of all management tools to reduce pest pressures during the cropping season.

In general terms, Dr Umina lists the following tips:

  • Knowing what the pest is
  • Knowing the beneficial insects
  • Understanding the local resistance issues
  • Assessing the risk of damage
  • Wherever possible, making use of economic thresholds to guide spray decisions
  • Following the Resistance Management Strategies now available, particularly rotating the use of different chemical groups (eg Table 2)

“Nurturing beneficial insects will reduce the need for insecticide sprays, however the application of many insecticides used in grain crops will kill beneficials if present,” Dr Umina says.

A key message is not to apply chemical sprays until absolutely necessary and reduce the use of prophylactic applications unless pests are known to become an issue.

Table 3: Growers' selection of control options for diamondback moth.
SeasonRisk factorsManagement recommendations
Summer–autumn – preseasonSummer rainfall can generate brassica green-bridge growth, which supports DBM (e.g. volunteer canola, lincoln weed, etc.). Abundant green bridge extending through March–April is a high risk for DBM colonisation of canola crops.Control brassica green-bridge to provide autumn DBM host break prior to canola sowing.
Pre-flowering cropGreater DBM risk in years with substantial greenbridge over summer and when dry conditions and/or above-average temperatures occur during autumn and winter.

Monitor at 3-4 week intervals from crop establishment using either visual inspection (up to the rosette stage) or a sweep net (stem extension onwards). Monitor more frequently in years of greater DBM risk. Grazing/grain: where possible manage DBM foliar feeding by strategic grazing. If unable to introduce stock to manage DBM, apply a Btk sprayab if the economic threshold (ET) is reached (refer to Table 2 below). (The same recommendations apply for forage brassicas.) Grain only: if the ET is reached apply a BtK sprayab.

Flowering/podding (grain only and grazing/grain crops)Greater DBM risk when weather is dry and/or temperatures are above average.Monitor crops using a sweep-net at fortnightly intervals throughout flowering to windrowing/harvest (more frequently when high risk). Sweep-net monitoring instructions Take a minimum of 5 sets of 10 sweeps in several representative parts of the crop and calculate the average number of the larvae (caterpillars) per 10 sweeps. Record the number of DBM larvae, the numbers of larvae of other moth pests (e.g., Helicoverpa) and the numbers of DBM natural enemies. Trends in these regular counts can be a good predictor of the effectiveness of natural enemies and/or the imminent need to spray. If the DBM ET is reached (refer to Table 2 below) an insecticide treatment is recommended. Insecticide choice: i) if controlling DBM alone, apply a BtKc , Affirm®d or Success Neo®d spray; ii) if controlling DBM and Helicoverpa larvae that are less than 8mm length, apply a Btkce, Btk plus VivusMax®e, Affirm®d or Success Neo®d spray; ii) if controlling DBM and Helicoverpa larvae* greater than 8mm length, apply either an Affirm®e or Success Neo®e spray. (*Helicoverpa ET: 4-5 larvae per 10 sweeps.). Good spray coverage is essential for achieving effective control of DBM. Note that dense canola canopies in spring require appropriate nozzle type, pressure and water volumesf . Continue to monitor the DBM population and natural enemy activity post spraying. In the unlikely situation that the DBM population again increases to the ET density, avoid consecutive use of the same product e.g. Use Success Neo® if Affirm® was applied earlier, or vice versa.
Consecutive yearsDBM infestations warrant spray treatment in consecutive years.In the second year avoid using the same product used in the previous year.

Insecticide Product Explanatory Comments
a Btk products conserve beneficials and are suited to the low UV conditions and lesser canopy area during pre-flowering.
b Sometimes pre-flowering crops are infested heavily by DBM and higher control may result from a chemical insecticide rather than a Btk product. In these instances, in fodder brassica crops Success Neo® is the only registered chemical product; in graze/grain canola crops Success Neo may be preferred because it has shorter grazing witholing period (7 days) than Affirm® (14 days); and in grain crops either Affirm® or Success Neo® is available.
c Btk products conserve beneficials, but are less suitable if the DBM density is rapidly increasing above the ET.
d Affirm® or Success Neo® are considered more suitable for rapidly increasing DBM populations, as they have greater persistence compared with Btk products.

e Btk sprays aimed at Helicoverpa require optimal conditions and small-sized larvae (no greater than 8mm). A mixture of Btk and VivusMax® is a biological insecticide option for Helicoverpa control.
f To achieve the necessary canopy penetration and coverage for late season DBM control use water volumes of no less than 100 litres/ha (ground applied). Air-induction nozzles or flat-fan nozzles greater than 110-03, spaced at 50cm, producing a medium spray quality have provided good control of DBM in canola crops and reduce drift when effective products at label rates are used.

“The challenge for growers and advisers is pest management decisions are not straightforward. Even the use of seed treatments can have negative consequences if used indiscriminately, including selecting for resistance,” Dr Umina says.
“Any species has the capacity to evolve resistance. 
“Good resistance management strategies for RLEM, GPA and DBM aimed at reducing the likelihood of new resistances developing and/or resistance spreading to new areas will assist growers in controlling their own populations and also lessen the resistance risk in other pests.”

cesar is providing a no-cost insecticide resistance screening service for grain growers suspecting a chemical control failure in RLEM and Lucerne flea. This service is being made possible through a GRDC investment being led by the University of Melbourne, in collaboration with cesar, the Western Australian Department of Primary Industries and Regional Development and CSIRO.

For RLEM, cesar is screening populations from all over Australia where control failures to neonicotinoid seed treatments are suspected; and populations from South Australia, Victoria, New South Wales and Tasmania where control failures to SPs and/or OPs are suspected.

For Lucerne flea, cesar is screening populations from all over Australia where control failures to foliar insecticides or seed treatments are suspected.

GRDC Project Code: UM00057; UM00048; CES00003; DAS00155

More information

Dr Paul Umina, 03 9349 4723, pumina@cesaraustralia.com (RLEM and GPA)

Mr Greg Baker, 08 8429 0933, greg.baker@sa.gov.au (DBM)

Additional resources

Redlegged earth mite Resistance Management Strategy fact sheet

Green peach aphid Resistance Management Strategy fact sheet

Diamondback moth Resistance Management Strategy fact sheet

Helicoverpa armigera Resistance Management Strategy fact sheet

GRDC Project code: UM00057; UM00048; CES00003; DAS00155