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Impact of MiridsRisk period: Mirids may be present at any stage from seedlings to late podfill but crops are at greatest risk from budding through to mid-podding. Mirid populations are typically low during the vegetative phase, but increase rapidly after budding. Nymphs will be visible within 2 weeks of adults entering the crop. Populations usually decline as pods mature. From R4-R5 (full seed - maturity), the crop is no longer susceptible to mirids.

Mirids (Creontiades spp.) are a major pest of mungbean crops, and are widespread throughout Australia. They are sucking insects that feed by piercing plant tissue. They have a preference for feeding on flowers, buds and young pods, causing these to abort, but will also feed on developing and maturing pods, causing ‘spotting’ of pods and seeds.

KEY POINTS• Mirids are major pests of flowering and podding mungbeans.

• Green and brown mirids are equally damaging.

• The most effective way to monitor for mirids is to use a beatsheet.

Damage: Mirids don’t ‘tip out’ vegetative terminals and cause no yield loss at the vegetative stage. However, in reproductive crops, they attack buds, flowers, small pods and seeds. Severe mirid damage can reduce pod set per raceme, and result in fewer seeds per pod. Be aware that similar symptoms (abortion of reproductive sites or reduced seed set) can also be caused by thrips, high temperatures or moisture stress. Mirids feeding directly on developing seed will cause marking on the seed coat and affect grain quality.

Treat all mirid nymph stages and adults as equally damaging. Trial work has shown that medium and large nymphs (instars 3-5) cause as much damage as adults. Although small mirid nymphs are less damaging, they develop so quickly they are also included in mirid density estimates.

Terminal showing poor pod set as a result of prolonged mirid feeding. Structures visible are nectaries which are not visible on racemes with good pod set. (Photo: Qld DAF)

SEPTEMBER 2015

Filling pods showing symptoms of severe mirid damage during podset – feeding wounds, darkening of pods, poorly filled seed. (Photo: Qld DAF)

Mirid damage to developing mungbean seeds at R3. Photo: Qld DAF)

Terminal

Set pod

Nectary

Tips and Tactics Mirids in Mungbeans

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Management StrategiesMonitoring: Mirids are very mobile and populations can increase very rapidly, both from immigration and hatching from egg lays. Inspect crops regularly to pick the start of budding, then monitor twice weekly from budding (R1) until post flowering (R4-5). In row crops, the recommended monitoring method is beat sheeting. This method is also the most effective for helicoverpa and podsucking bugs. In crops on <50 cm row spacing, sweep netting is a viable option for mirids but is inadequate for other key pests.

Cultural control: Shortening a crop’s flowering period reduces length of time the crop is at risk of mirid damage.

Natural enemies: Spiders, ants, predatory bugs, predatory wasps and predatory mites have been observed attacking mirids in the field. Naturally-occurring pathogenic fungi (e.g. Beauvaria) may also infect and kill mirids, but are rarely observed in the field as infection requires very high humidity. At low densities, natural enemies may exert some suppression of mirid populations, but are unlikely to impact on mirid densities above threshold levels. However, preservation of natural enemies is still important for the ongoing suppression of other pests like helicoverpa.

Thresholds: Cross-reference the cost of control (pesticide plus application) against crop value to determine the economic threshold (ET). Table 1 shows

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the thresholds for a range of crop values and control costs. Thresholds are based on a yield loss of 60 kg/ha per mirid/m², assuming continuous mirid activity over a 28-day period during the budding-podding (R1-R5) stages, and sampling with a standard beat sheet.

IdentificationMirid adults are elongated pale green or brown bugs 7 mm long with long legs and long antennae.

Green mirid adults are uniformly pale green.

Beat sheeting is the preferred method for assessing mirid populations in mungbeans. (Photo: Qld DAF)

Control Cost $/ha

Mirid thresholds* (adults + nymphs/m2) atmungbean crop values below

$500 $600 $700 $800 $900 $1,000 $1,100 $1,200

$10 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.1

$15 0.5 0.4 0.4 0.3 0.3 0.3 0.2 0.2

$20 0.7 0.6 0.5 0.4 0.4 0.3 0.2 0.2

$25 0.8 0.7 0.6 0.5 0.5 0.4 0.4 0.3

$30 1.0 0.8 0.7 0.6 0.6 0.5 0.5 0.4

$35 1.2 1.0 0.8 0.7 0.6 0.6 0.5 0.5

$40 1.3 1.1 1.0 0.8 0.7 0.7 0.6 0.6

Table 1: Economic threshold chart for mirids in mungbeans.

* Chemical control: Dimethoate is the cheapest and most effective pesticide for mirids in mungbeans. Dimethoate at lower-than-label rates (typically 250 mL/ha), with a 0.5% salt adjuvant, provides excellent control and has significantly less impact on most beneficial insects. ‘Hard’ water markedly reduces dimethoate’s effectiveness and must be countered with a buffering agent such as LI700. Dimethoate use is currently under Permit 13155, valid until 5 Oct, 2015, but likely to be extended. Check the APVMA website (www.apvma.gov.au) to determine dimethoate’s permit status post 5 Oct, 2015.

If the crop is healthy and growing well, it will compensate for damage done in the first week after budding. By delaying the first mirid spray by up to 7 days, additional sprays may be unnecessary, thereby reducing the risk of flaring helicoverpa (which are usually more costly to control). In moisture-stressed crops, do not delay mirid control as the capacity of the crop to compensate for early damage will be restricted. Continue to monitor throughout the risk period, even if mirids have been controlled, as crops may be reinfested by influxes of mirids.

Green mirid adult (8mm in length). (Photo: Qld DAF)

The brown form (left) and the green form (right) of the adult brown mirid (12mm). (Photos: Qld DAF)

Brown mirid adults have two distinct colour forms:

• Brown form - light brown with darker pigmentation on hind legs

• Green form - bright green with dark red (purple-brown) pigmentation of the head, thorax and hind legs.

Mirids in Mungbeans Tips and Tactics

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Mirid nymphs are elliptical-shaped and lack wings. Young nymphs have antennae much longer than their body. First instar nymphs are pale brown/orange in colour but later instars are green. Green mirid nymphs have pale antennae while brown mirid nymphs have distinctive red-brown and white banding on the antennae. Mirid eggs are pale and elongate and are inserted into plant tissue, so are not readily visible. Scouting for mirid eggs is not recommended.

Similar species that may be confused with green and brown miridsBrown mirid adults may be confused with the predatory damsel bugs. Mirids have longer antennae, are not quite as slender, and have a less prominent proboscis (elongated mouthpart used to pierce the plant).

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Broken back bugs and crop mirids are similar in appearance to green mirids. Broken back bugs have a distinct downward sloping back. Crop mirids have grey-green wings and bright green bodies. Nymphs are green with brown, striped antennae, and a characteristic black spot in the middle of the back.

Green mirid adult (8mm in length). (Photo: Qld DAF)

Damsel bugs are one of the natural predators of mirids, and may be confused with brown mirids. (Photo: Qld DAF)

Australian crop mirid. Left: Adult (6mm). Right: nymph (3.5mm). The arrow indicates the location of the characteristic black spot.

Green mirid nymphs. From left: 1st, 2nd, 3rd, 4th and 5th instar (not to scale). Note the developing wing buds from 3rd-5th instar (Photos: Qld DAF)

Brown mirid nymphs. From left: 1st, 2nd, 3rd, 4th and 5th instar (not to scale). Note the developing wing buds from 3rd-5th instar (Photos: Qld DAF)

Mirids in Mungbeans Tips and Tactics

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DISCLAIMERAny recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Grains Research and Development Corporation. No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. The Corporation and contributors to this Fact Sheet may identify products by proprietary or trade names to help readers identify particular types of products. 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 to. The GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication.CAUTION: RESEARCH ON UNREGISTERED AGRICULTURAL CHEMICAL USEAny research with unregistered agricultural chemicals or of unregistered products reported in this document does not constitute a recommendation for that particular use by the authors or the authors’ organisations.All agricultural chemicals must accord with the currently registered label for that particular agricultural chemical, crop, pest and region.Copyright: All material published in this Tips ‘N’ Tactics is copyright protected and may not be reproduced in any form without written permission from the GRDC.

More information

See the GRDC GrowNote on mungbeans at www.grdc.com.au/GrowNotes

Acknowledgements

Hugh Brier, Qld DAF

Melina Miles, Qld DAF

Tonia Grundy, Qld DAF

Produced by Seedbed Media www.seedbedmedia.com.au

Figure 1: The life cycle of mirids in mungbeans, and critical monitoring and control timing. Egg development is relatively slow, taking as long as 7-10 days. Mirid development (egg hatch to adult) is very rapid, taking only 12-16 days at 30 degrees celsius. There are 5 nymphal stages.

Mirids have no impact on yield

Optimal spray timing

Crops at greater risk in hotter seasons. No mirid damage until budding.

Note: Mungbeans are an indeterminate crop and crop stages usually overlap. In some season there may be more than one flower flush.

Critical monitoring period

for this pest

VE-V3 R1-R3

FloweringBudding Podset

R4-R6 Harvest

Vegetative

Adults

Eggs

Nymphs

Podfill Harvest

Mirids in Mungbeans Tips and Tactics