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 firstname.lastname@example.org
For more information on seedling thrips visit www.thebeatsheet.com.au/crops/pulses/mungbeans/seedling-thrips-in-spring-mungbean-crops/
Caption: Seedling thrips damage on a crop near Goondiwindi.
Elise McKinna, Media & Communication Officer
Department of Agriculture, Fisheries and Forestry
(07) 3087 8576 or 13 25 23
Sarah Jeffrey, Senior Consultant Cox Inall Communications