Entomologist Liz Williams said there have been reports of Monolepta at populations of more than 50 beetles/m2 in Burdekin mungbean crops. Monolepta are considered at damaging levels when numbers exceed 10 beetles/m2. Photos courtesy QDAF.
Burdekin mungbean growers are being advised to be vigilant about pest control after outbreaks of red-shouldered leaf beetles were detected in crops throughout the region.
Red-shouldered leaf beetles or Monolepta have the potential to significantly impact yield and have been identified in North Queensland crops at more than five times the acceptable crop threshold.
Queensland Department of Agriculture and Fisheries entomologist Liz Williams said Monolepta were considered at damaging levels when numbers exceeded 10 beetles/m2.
“There are reports of Monolepta at populations of more than 50 beetles/m2 in Burdekin mungbean crops, which are mostly at early podding or podfill stage.
“The beetles have been observed shredding leaves, consuming flowers and making holes in pods, sometimes reaching and damaging the seeds. These holes in the pod also increase the risk of water-staining in seeds (from rain or overhead irrigation), which reduces bean quality.
“Monolepta larvae feed on grass and cane roots and then pupate underground, which is why invasions typically first appear around crops edges. Mass emergences can be triggered by rain events. Monolepta also release an aggregating pheromone, attracting more adults into the crop.”
She said it was also critical the pest was correctly identified, because Helicoverpa was also capable of causing holes in mungbean pods, although these were typically more widely spaced and less in number per pod compared to the ragged and closely spaced holes of Monolepta.
Monolepta damage on leaves.
Dr Williams advised growers to scout and sample crops to determine if Monolepta were present at damaging levels and assess their distribution throughout the crop.
“If Monolepta are only present at the edges, growers are advised to treat a boom width into the crop to target the current infestation and reduce beetle spread,” she said.
“Targeted spraying will both save money and reduce pesticide impact on key predators of other pests, especially ladybirds. Prompt action is critical to minimise the risk of Monolepta releasing aggregating pheromones, which results in large, crop-wide infestations.”
Dr Williams said the product registered against Monolepta in soybeans was Steward (indoxacarb) at 200 mL/ha. But she said Steward was not registered for the control on Monolepta in mungbeans and at this time there was no permit for this particular situation.
Growers who detected Monolepta in mungbean crops are asked to report major outbreaks and direct inquiries to the DAF/CSIRO entomologist team Liz Williams, 0476 850 415 Liz.firstname.lastname@example.org, or Hugh Brier, 0428 188 069, Hugh.email@example.com, or Steve Yeates, 0417 015 633, Stephen.Yeates@csiro.au
Liz Williams, QDAF, 0476 850 415
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