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Crop Grazing Shows Promise As Disease Tool

09 August 2011

AUSTRALIA - South Coast researchers may have uncovered a new tool to help farmers manage barley powdery mildew - crop grazing. Preliminary results from a Grains Research and Development Corporation (GRDC) supported trial at Gibson showed crop ‘grazing' significantly reduced levels of the disease in barley, compared with ungrazed crops.

For ease of management, the trial used a roller and lawnmower to simulate the effects of livestock. Barley powdery mildew causes annual losses of about $30 million to WA’s barley crops, and the risk of damage has recently increased due to strains resistant to the triazole group of fungicides.

Alternative management options such as grazing, and reduced reliance on costly full spectrum seed fungicides, could help farmers deal with disease resistance resulting from selection pressure from fungicide use.

The trial is being conducted by the Department of Agriculture and Food (DAFWA) as part of the GRDC’s ‘barley agronomy for the western region’ project.

DAFWA researcher Andrea Hills said that in July, more than 5 per cent of the lower leaves of ungrazed Baudin barley in the trial were infected by powdery mildew – the level at which the crop would normally be sprayed with fungicide.

“However, visual scoring showed the ‘grazed’ Baudin barley plots were clean,” Ms Hills said.

“Although this is an introductory trial, these initial results show that crop grazing could be a useful tool in an integrated approach to early season disease management, with the huge added bonus of providing feed for livestock.

“We still need to find out if barley yields are reduced by crop grazing, if disease levels are still reduced in spring, and if there is any impact on barley grain quality for malting, which is critical.”

Ms Hills said she conducted the trial following anecdotal evidence that crop grazing by sheep or cattle reduced the damage caused to local barley crops by powdery mildew.

“As far as I’m aware, no-one has previously studied the impact of grazing on disease in malting barley crops,” said Ms Hills.

Ms Hills said the primary aim of the trial was to find out if growers could avoid having to apply an early fungicide spray by grazing their crops.

In the trial, an inexpensive fungicide seed dressing – protecting the crop from smut but not powdery mildew – was applied to some plots while in others a dressing registered for early mildew control and insect protection was used.

“If grazing is able to reduce disease levels in the early stages of growth then the more expensive seed dressing may be unnecessary, saving money that may be better spent on the new generation fungicides that are still effective against barley powdery mildew,” Ms Hills said.

“Seed dressings containing an insecticide also have longer withholding period before crop grazing can commence (up to ten weeks post sowing).”

Baudin barley – a commonly grown variety susceptible to powdery mildew – was seeded on May 11, and rolled using a pea-roller to simulate the effect of livestock trampling the crop and levelling the furrows.

The crop was mowed for about a six week period until the ‘first node’ appeared on the crops – the critical point at which to stop grazing crops to avoid yield losses.

TheCropSite News Desk

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