Leaf beetles in Burdekin pulses

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Rhyparida adult

Rhyparida sp. (swarming leaf beetles) have been reported in some Burdekin soybean crops. While the risk of outbreaks has declined as leaves dry off, growers and consultants are reminded to keep a lookout for this sporadic but sometimes very damaging pest. Monolepta sp. (redshouldered leaf beetles) have also been observed in some crops.

What to look for

Dead leaves are usually the first sign of Rhyparida attack. Look for damage to the petioles, particularly feeding tunnels made by the beetles. This tunnelling damages the vascular tissue in the petioles leading to the death of petioles and the leaves attached to them. Rhyparida beetles are quite small (6-7 mm long) and are varying shades of brown. There may be a number of species but they inflict the same type of damage. Sometimes they are parasitised by bright red ticks which reside under their wing covers.

 

Rhyparida damage – chewed through petioles and dead leaves (photo by Hugh Brier)

Other leaf beetles

Monolepta adult

Monolepta beetles are similar in size, but are bright yellow-orange with a dark red band across their shoulders. They tend to shred leaves when in high numbers and will also attack flowers and pods.

Damage by leaf beetles is often patchy, and can be more common close to field edges, particularly near eucalypt windbreaks, native vegetation, or sugarcane. The latter is a strong risk factor as their larvae feed on cane roots and stools.

Monolepta attacking mungbean leaves and flower buds (image from Paula Mizzi, Northern Agri-Services, Ayr)

Thresholds

Thresholds for leaf beetles are usually based on a percentage of dead leaves. Up to 33% dead leaves or 33% defoliation is tolerable during the crop’s vegetative stage but this decreases to 16% during the podfill stage. In mungbeans and soybeans, control is warranted when swarms of the beetles are attacking buds, flowers and pods.

Control

No insecticides are registered for Rhyparida beetles, but indoxacarb (Steward®) is registered at 200 mL/ha against Monolepta in soybeans. Indoxicarb can be used at the same rate against Monolepta in mungbeans (Permit 83624 until March 2023) and against Rhyparida in soybeans and mungbeans (Permit 88878 until December 2020).

Outside the helicoverpa resistance management windows for Steward®, other products may have potential but efficacy data is required before any permit can be secured. To assist us in our investigation of future options, please report any leaf beetle outbreaks to your local DAF officer (Brock Dembowski DAF Townsville 0467 819 592) or Hugh Brier DAF Kingaroy 0428 188 069.

Further information

Beetle photos by Joe Wessels. 

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