Last week’s rare November frost raised concerns about an unusual disorder in grain sorghum crops.

Queensland Department of Primary Industries and Fisheries (DPI&F) principal plant pathologist in Toowoomba, Malcolm Ryley, said he had received young grain sorghum plants to check for possible disease-causing organisms.

Dr Ryley said that apart from some minor root infection, the plants had no disease, but were affected by the light frosts in much of the southern Queensland grain belt and northern NSW.

He said the damage was worsened by the cold winds that followed.

Dr Ryley said some upper leaves of the plant samples showed distinct bleached to light brown stripes. Other leaves had general “burnt” patches, without the striping.

“In most cases the damage was confined to the top one-third of plant leaves,” he said.

Dr Ryley said the plant samples came mostly from low-lying parts of paddocks, again pointing to frost damage.

When plant stems were cut, there was no damage to developing leaves or other internal parts of plants.

He said the plant damage he saw would grow out and was unlikely to reduce yield, but concerned growers should contact their agronomist to assess their individual situations.

“There may be some issues with pollen viability in damaged plants that are at the flag leaf stage, but I feel it’s unlikely to be an issue in less mature plants,” he said.

The plant disease concerns resulted from the rarity of frost damage to grain sorghum in November, Dr Ryley said.

DPI&F senior industry development officer Greg Salmond said government and private agronomists were working together to assess the frost damage and provide growers with options that suited their circumstances.

Mr Salmond said that generally there had been less damage than expected, although some individual crops in low-lying areas were severely affected.

He said the hardest hit area was the southern Downs. Maize and dolichos generally sustained more damage than grain sorghum.

“In many cases crops will recover from the damage. Some growers may consider slashing or replanting in extreme cases.

“We recommend that growers inspect their paddocks and seek professional advice if they have concerns,” Mr Salmond said.