Crown rot

Crown rot is a fungal infection that attacks the base (crown) of cereal plants, disrupting water and nutrient supply to the developing head. Cereals affected are:

• durum
• wheat
• barley
• oats.

Identify and recognise symptoms

• Crown rot identification can be made by looking at the base of the wheat plant, which will have a brown discolouration of the stem base.
• Pink/red fungal growth may also be present.
• Crown rot results in the droopy 'white head' appearance within the crop.
• Most of these heads will contain no grain or very pinched grain at harvest.
• It is important to note that crown rot can still be present in the crop even if the whiteheads are not visible and that yield losses can still occur in these crops.
• Correct analytical diagnosis of Crown Rot and also the level of infection present can be done by sending stubble away for diagnosis.

Cause, prevalence and severity

Crown rot results in crop yield losses.

Unfortunately, crown rot is difficult to manage as it has a very good survival method within the stems and crown of cereal plants and other hosts such as:

• barley grass
• wild oats
• phalaris.

Water stress is the main reason for the visual expression of crown rot, so it is often first seen:

• in paddocks along wheel tracks
• surrounding trees
• in paddocks with a high nitrogen content, where the crop has grown vigorously and then run out of moisture toward the end of the season.

The presence of crown rot gives an indication of the risk and potential magnitude of yield losses.

The presence of crown rot inoculum does not always translate into high crop losses.

A wet finish to the season can reduce the damage caused by crown rot but will not prevent yield losses in all cases.

Manage the condition

If crown rot is left unmanaged it will remain in dead and living material within the paddock from season to season.

A common misconception is that stubble burning or cereal stubble grazing are both effective control methods for Crown Rot.

Burning stubble is not a reliable method as it only reduces the plant material on the soil surface and the crown rot fungus can still survive in the plants crown material that is unburnt or is beneath the soil surface. Grazing can have a similar result.

Grazing of stubble, cultivation and stubble mulching can result in fragmentation of the infected plant material into inter-row spaces and may spread the infected material across a larger area of the paddock.

The most reliable methods for reducing fungal levels and controlling crown rot are:

• crop rotation with crops such as:
  • legumes (field peas, chickpeas, faba beans)
  • canola
  • sunflower
  • sorghum
• a break of more than 12 months between cereal crops to reduce inoculants levels with a denser break crop canopy increasing the breakdown of infected cereal residue
• a lucence pasture phase within a mixed farming enterprise to allow for an extended break between cereal host crops
  • control of grass weeds is essential during the pasture phase
• good farm hygiene controlling all grass weeds within paddocks, fencelines, roads etc.
• inter-sowing cereals between previous years cereal stubble to limit the physical contact with infected residues of previous crops and reduce infection by up to 50% in new plants.

You can also reduce the impact of crown rot by:

• planting wheat varieties with greater resistance to crown rot and root lesion nematodes. Consider varieties such as such as Longreach Spitfire, EGA Wylie and Sunguard.
• reducing the potential moisture stress of a crop through:
  • good fallow management
  • in-crop weed control
  • matching nitrogen levels to plant requirements
  • avoiding very high plant populations.