Grains Research and Development

Date: 30.10.2014

Thrips threaten spring mungbean crops

Author: Sarah Jeffrey
Image of seedling thrips damage on a crop near Goondiwindi.

The Grains Research and Development Corporation (GRDC) is advising mungbean growers to be on alert for insect activity following recent reports of seedling thrips damage in spring crops near Goondiwindi.

Seedling thrips (Thrips tabaci) are also known as win­ter cereal thrips or cotton seedling thrips and commonly move from maturing win­ter cere­als onto new green spring growth in mung­bean, navy bean or cot­ton crops. 

According to Department of Agriculture, Fisheries and Forestry (DAFF) senior entomologist Hugh Brier, thrips damage poses the greatest risk to spring mungbean crops but he said early damage rarely translated into yield loss.

“In most cases thrips dam­age is largely cos­metic and will not com­pro­mise yield or matu­rity,” Mr Brier said.

“How­ever if thrips from sur­round­ing cereal crops keep invad­ing mung­bean over an extended period of time, they could impact on plant growth and ulti­mately yield.”

While no thresh­olds currently exist for seedling thrips in mung­bean, Mr Brier said thresh­olds in seedling cot­ton of 10 thrips (adult and lar­vae) and 80% dam­age to leaves may pro­vide a guide for control decisions.

“Thrips dam­age to new leaves is inflicted in the ter­mi­nal before they emerge and expand so spray­ing spray now won’t undo cur­rent dam­age but it would pre­vent future dam­age,” he said.

“It’s important to remember that the pesticide’s impact may not be imme­di­ately obvi­ous as leaves yet to emerge may have already been damaged.

“If growers fear an extended thrips inva­sion and do opt to spray, we highly recommend leaving some unsprayed strips to deter­mine if the spray was worthwhile and allow for an assessment of crop recovery.

“It would also be use­ful to pho­to­graph tagged plants over time in sprayed and unsprayed parts of the crop to ascer­tain whether there is a vari­a­tion in time of flow­er­ing and matu­rity, and yield.”

Adult thrips are 2mm long, are dark cigar shaped and have nar­row feath­ery wings folded along their back. Lar­vae are smaller, lack wings and are pale.

Lar­vae feed inside veg­e­ta­tive ter­mi­nals whereas adult thrips tend to infest a seedling’s grow­ing point as soon as it emerges from the ground. In the case of crack­ing soils, seedlings may even be infested before they emerge. Pop­u­la­tions typ­i­cally peak within four weeks of plant emer­gence.

Dam­aged leaves can be severely dis­torted and dis­coloured and may resem­ble her­bi­cide (2,4-D) damage.

Any out­breaks should be reported to Hugh Brier on (07) 4160 0740 or 0428 188 069 or email hugh.brier@daff.qld.gov.au

For more information on seedling thrips visit www.thebeatsheet.com.au/crops/pulses/mungbeans/seedling-thrips-in-spring-mungbean-crops/

ENDS

Caption: Seedling thrips damage on a crop near Goondiwindi.

Contact Details

For Interviews

Elise McKinna, Media & Communication Officer

Department of Agriculture, Fisheries and Forestry

(07) 3087 8576 or 13 25 23

media@daff.qld.gov.au

Contact

Sarah Jeffrey, Senior Consultant Cox Inall Communications

0418 152859

sarahj@coxinall.com.au

Region North