Crown rot remains a threat under irrigation

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Cotton growers moving into irrigated grain production are being warned to manage the damaging cereal disease crown rot, which can cause major yield losses when moisture stress occurs during grain fill.

NSW Department of Primary Industries (DPI) plant pathologist Dr Steven Simpfendorfer says irrigated grain can have a greater risk of loss to crown rot because irrigated grain targets higher yields, which have higher water and nutrition requirements.

Dr Simpfendorfer says bulky crops have much higher water use during grain fill. “If soil reserves are not adequate or supplemented with irrigation during this critical period then the resulting moisture stress can cause significant development of whiteheads from the crown rot infection in the base of plants,” he says.

“Losses to crown rot can be dramatically reduced in irrigated crops by a range of management options and carefully considering the scheduling of water to limit moisture stress during grain fill.”

GRDC-supported research shows that the best way to avoid yield losses due to crown rot is using crop rotations to limit the build-up of crown rot inoculum in winter cereal stubble.

“This makes it vital that growers know the crown rot status of their paddocks prior to sowing,” Dr Simpfendorfer says. “Exposure to reduced yields from crown rot infection is dependent on the combination of two factors: first, the level of crown rot inoculum in cereal stubble or grass weeds, and second, the degree of crop moisture stress later in the season.

“This effect is intensified if the plant is stressed at, or after, flowering, where infected tillers produce a whitehead that has either no grain or pinched seed.”

Non-stressed crops will tolerate even moderate levels of crown rot with only minor reductions in yield.

“Variety and rotation choice at the paddock level should take into account the risk associated with crown rot,” Dr Simpfendorfer says.

He says the risk of crown rot should be evaluated based on either visual assessment of the extent of basal browning near harvest of a cereal crop, or by commercial stubble testing through Crown Analytical Services at Narrabri, NSW.

Various management options include:

* rotating out of the crown rot cycle into a winter break crop or fallow for a summer crop if there is a high level of crown rot inoculum; any moisture stress even in partially resistant varieties may impact on yield dramatically;
* choosing a partially resistant bread wheat variety and limiting moisture stress if there is a low level of crown rot inoculum in the paddock, especially at flowering and during grain fill; and
* if there is no crown rot inoculum in the paddock, choosing varieties according to other factors – take advantage of high-yielding and/or value varieties that have poor resistance to crown rot, such as durum wheats.

GRDC Research Code DAN00122

More information: Cotton and Grain Irrigation, www.cottonandgrains.irrigationfutures.org.au