Pulses play their part in CR control by Gary Alcorn

Wheat plants that have succumbed to crown rot. Inset: Crown rot lesions

In response to grower concerns and the recent history of serious disease outbreaks, particularly crown rot, the latest Grains Research Updates in the northern grains region have focused on management responses to crop disease with a particular emphasis on healthy rotation crops. Here, and on pi of this issue, we cover some of the latest good advice and information on this subject arising from the update series. Another update focus was opportunity cropping and subsoil characteristics, and you 11 find some of the latest research in these pages as well.

THE SICKNESS of the 'parents' is visited upon their children when it comes to crown rot in wheat.

QDPI Principal Plant Pathologist Graham Wildermuth told farmers at recent Grains Research Update meetings at Moonie and Weengallon in south-western Queensland that a characteristic honey-coloured discolouration at the stem base had serious implications for the following wheat crop.

"If the level of discolouration is above 20 per cent, losses may be experienced in the following crops if there is a dry spring," he said.

Crown rot (CR) can be tackled through a combination of crop rotations, grass removal, resistant wheat varieties, nitrogen monitoring and possibly an autumn stubble burn.

Dry spring a warning sign

Growers should include in their assessment any prediction of a dry spring, which may cause moisture stress at or after boot stage, triggering deadhead or whitehead development.

"Crown rot is a disease of the stem bases of wheat and barley. CR fungal threads survive in the residues of diseased winter cereals or infected grasses. From these diseased residues the fungus grows to infect plants in the next season.

"Stubble burning will reduce the level of the disease in a subsequent winter cereal but as there may still be disease residues below the surface of the soil, the disease will not be completely controlled. Another option is to burn stubble before the last wheat crop in a rotation and so reduce the level of crown rot and increase the effectiveness of the rotation crop," Dr Wildermuth said.

Rotations most effective

A less disruptive tactic — crop rotation — is the most effective means of controlling CR, according to Dr Wildermuth. Summer crops, pulses, lucerne and medic pastures are effective 'break' crops that disrupt the disease cycle provided they are grown for at least two years.

While grain sorghum is a suitable rotation crop under most circumstances, emerging data suggest it can harbour CR disease if planted after a winter crop with a high CR level.

"Crop rotation reduces crown rot by removing the food base needed by the fungus. Grasses such as phalaris, barley grass and wild oats should be controlled promptly so they cannot maintain the fungus during the rotation cycle," he said.

Other CR promoters

Other factors favouring a CR explosion include high soil nitrogen, low zinc levels, and choosing highly susceptible durum varieties whereas Sunco, BaxterPBR logo and LangPBR logo are partially resistant.

Dr Wildermuth encourages active monitoring of wheat crops post-flowering to detect and determine the level of honey-coloured discolouration at the stem base which (above 20 per cent) can point to substantial grain losses in the next wheat crop.

Program 1 Contact: Dr Graham Wildermuth 07 4639 8805 email Graham.Wildermuth@dpi.qld.gov.au

Region North