Fungicide not the solution to black spotting on barley
Growers are being warned not to spend valuable dollars on fungicide sprays in an attempt to halt the recent black spotting on barley crops in the northern region.
Unusual weather patterns over the past two months are largely being blamed for a rise in the incidence of black spots on the leaves of barley crops.
The Grains Research and Development Corporation (GRDC) said leading pathologists in Queensland and New South Wales had recently been fielding a number of calls regarding spotting in barley crops.
Department of Agriculture, Fisheries and Forestry (DAFF) principal pathologist Greg Platz said there was a lack of evidence to suggest that the black spotting was caused by spot form net blotch and fungicide applications would be a costly and ineffective means of control.
“It is logical to conclude that the black spotting we are currently seeing on some barley crops in the northern region may be spot form net blotch as the symptoms are very similar to the early stages of the disease,” Mr Platz said.
“Spot form net blotch has seldom been isolated from samples tested and we believe the cause is physiological leaf spotting (PLS), or oxidative stress, largely as a result of current environmental conditions.
“A mild start to winter followed by the rapid change to cold, frosty weather in July will have affected plant function.”
Mr Platz said other factors that may have contributed to the current symptoms in barley crops included interaction with herbicide, varietal susceptibility to PLS and exposure to high levels of light.
Black spotting occurs when plants overproduce reactive oxygen species (ROS) in response to stress.
These ROS react with other cell compounds forming small to large brown or black spots, meaning that most of the spotting currently being observed in crops is the result of a biochemical reaction and not fungal infection.
Mr Platz said some varieties appear particularly susceptible to PLS and spots may be up to 20mm long.
DAFF and the NSW Department of Primary Industries have also had a number of enquiries from agronomists and consultants regarding yellowing in crops of wheat and barley.
Mr Platz believes similar issues are to blame – cold conditions (particularly frost), environmental influence on herbicide applications and in some cases, soil nitrogen deficiency.
Caption: Spotting occurs when plants overproduce reactive oxygen species (ROS) in response to stress. Photo supplied by DAFF.
Elise McKinna, DAFF Media & Communication Officer
07 3087 8576
Sarah Jeffrey, Senior Consultant Cox Inall Communications
0418 152 859
GRDC Project Code DAQ00187