Bugs put bite on massive Qld sorghum crop

Tuesday, January 08, 2008

The threat of pest infestations could dent Queensland's massive sorghum crop potential.
Agronomists in both Central and Southern Queensland this week warned grain sorghum growers their crops may be battling large in-crop infestations of Rutherglen bugs (RGB).

Department of Primary Industries and Fisheries acting science leader, Dr Melina Miles, said growers had taken advantage of widespread late spring and summer storm rains to plant grain sorghum.

But Dr Miles said growers should be checking their crops for RGB infestation from flowering through to the end of grain fill because adult insects will feed on the seed as it sets and fills.

"Our preliminary research into the impact of RGB on sorghum indicates that adult insects will reduce seed set by 20pc at densities of between 50-100 bugs per head," Dr Miles said.

"At higher bug densities, seed set may be reduced even further.

"Where bugs infest the crop after the grain has been set, adult RGB will feed directly on the seed.

"Affected seed looks spotty and dark and the inside is often blackened or hollow as a result of RGB feeding.

"This allows fungi and bacteria to infect the developing seed and the resultant seed set is discoloured, small, shrivelled and lightweight and likely to be lost at harvest."

Dr Miles said growers should consider protecting their sorghum seed set when the RGB threshold reaches 25–50 adults per head by spraying with a registered synthetic pyrethroid pesticide at the same application rate recommended for Helicoverpa caterpillar control.

"Crops are at greatest risk from RGB damage during the development and grain filling stage but treating the adult population will not deliver any guarantee that the crop will not be reinfested overnight if climatic conditions favour the insect," Dr Miles said.

Dr Miles said inspections of some Darling Downs sorghum crops planted in late September through to early November indicated that 80pc of viable seed had been lost.

Dr Miles said DPI&F researchers were currently investigating the efficacy of the insect fungal disease Metarhizium for use as a biopesticide control option for RGB.

"If our trials show this is effective, it will be an important addition to the Integrated Pest Management cropping recommendations for sorghum," Dr Miles said.

Sourced from FarmOnline.