Rhizoctonia

Rhizoctonia is a soil born fungal disease which causes root pruning, being most prominent in dry seasons due to the reduced access to nutrients and moisture. The greatest yield losses are normally seen in good seasons.
Barley is the most severely affected, followed by wheat, triticale and oats.
Grassy pastures and intensive cereal rotations increase levels of inoculum.
Wet spring and summer conditions will help breakdown inoculum prior to sowing, provided that weeds are controlled during the fallow.
Sowing as early as possible with a tined seeder can help minimise Rhizoctonia infection.
Fungicide applied to the seed or fertiliser can also reduce infection rates.
Avoidance of pre-emergent herbicides which cause root pruning will also help to reduce disease severity.
Longer term control is achieved through sound crop rotations.

Take-all

Take-all is a cereal disease most often observed post flowering, by the premature haying off of patches within the crop. Affected plants generally contain no grain, are easily pulled from the ground and have a blackened crown. Yield loss in severe cases can be in excess of 50%.
Wheat and triticale are most susceptible, with barley and oats less affected.
Paddocks most at risk in 2021 are those which were in a cereal in 2020 or those which were previously a grassy pasture. Growers with seeders providing limited cultivation and those having soil pH levels above 5.0, are at an even greater risk of infection.
Moisture over summer will reduce inoculum levels for next season.
Grass weeds over summer can build up Take-all levels if soil temperatures are cool.
One clean break crop will significantly reduce inoculum levels in seasons with adequate moisture.
Later sowing will lead to greater breakdown of inoculum.
Reducing pre-emergent herbicides can reduce severity of Take-all, as the crop has a more resilient root system.
Fungicide treatments on the seed and fertiliser can reduce infection levels.
Adequate nutrition may help reduce the severity of the disease.
Rotation of broadleaf crops with cereals is the most effective long term control measure.

Crown Rot

Crown Rot causes yield loss in cereals due to restricting moisture flow from the roots to the head during grain fill. It is often observed as individual white heads, with a brown or pink discolouration of the crown. Moist autumn conditions coupled with a dry spring favour disease expression in cereal crops sown back to back.
Cereal crops ranging from least sensitive to most sensitive are barley > bread wheat > triticale > durum. Wheat varieties also display a variation in susceptibility to the disease. Therefore under high disease pressure situations and where wheat is required to be grown, a more resistant variety should be chosen.
Inoculum levels are directly correlated with stubble loads during the early post-emergent phase of the crop. Reducing the chance of stubble contacting seedlings is the most effective method of reducing disease occurrence. Burning stubble and inter-row sowing are ways of achieving this.
Most winter growing grasses host Crown Rot.
Fungicides are not effective in controlling Crown Rot.
Cultivation will damage the Crown Rot hyphae and reduce infection. Disc seeders can be particularly problematic as they generally operate in high stubble load environments and do not cultivate the soil.
Early sowing should reduce the yield loss associated from Crown Rot infection.
A single year of broadleaf crop is not reliable in reducing the inoculum levels significantly. However a “double break” of two successive broadleaf crops does appear to be effective in managing the disease.

Blackleg

Blackleg is a disease which can infect seedling canola and cause yield loss through crown cankering, when infection occurs prior to the 6 leaf stage. Infections later in the season infect the stem, flowers and pods, resulting in branch loss, pod abortion, reduction in seed size and increased pod shattering.
Blackleg is a fungus which can sexually reproduce and release spores from decomposing canola stubble that infects growing crops.
Canola varieties have resistance genes bred into them; however, they vary between variety with some resistance genes having been overcome by the disease. Genes which currently provide good protection include groups D and H.
To reduce the duration of spore release from stubble, the stubble should ideally be smashed and put in contact with the soil to speed up decomposition. A wetter than average summer and autumn should reduce Blackleg inoculum levels, as this will increase the speed of decomposition.
Physical separation from previous years’ stubble is one effective method of reducing disease pressure, especially downwind from the previous years’ stubble.
Seed and fertiliser fungicide treatments aid in the control of seedling infection, with foliar fungicides effective in high pressure situations. Foliar fungicides are also effective against upper canopy Blackleg infections. However in high disease pressure situations, multiple passes may be required to provide adequate control for the entire flowering and podding stage of the crop.

Crop Diseases to be Aware of for 2021 Planning