WA yields go hot and cold

Jo FulwoodThe West Australian

Widespread frosts over parts of the central and southern Wheatbelt exacerbated by an extended heat-stress period at the end of September could see millions wiped from WA crop returns this season.

Department of Agriculture and Food frost expert Ben Biddulph said while the frosts had not been extremely severe or widespread, there had been patchy damage to flowering and susceptible crops right across the region.

Dr Biddulph said temperatures fell to -1C and -2C across wide sections of the agricultural regions over successive nights throughout September, and growers should now be on the lookout for frost-damaged florets, shrivelled grains and white-blistered stems, particularly in wheat.

He said frost could cost WA growers upwards of $120 million in severe years such as 2008.

But he said this year's damage would not be as severe or widespread.

In contrast, GRDC's external Investment Plan 2016-17 estimates annual economic losses from heat damage at $230 million for growers in WA.

GRDC Western Panel chairman Peter Roberts said heat damage caused losses upwards of 100kg/ha for every day over 25C during flowering. "So in 10 days you can massively reduce the amount of grain in your crop, and that happened in the northern Wheatbelt last year, and it looks to be happening right across the Wheatbelt this year," he said.

"Heat is so insidious that you can't see the damage like frost and you only know the impact when you put the header in the paddock."

Mr Roberts said the GRDC Western panel had identified heat damage as a research priority for the coming years, as identified by the external investment plan.

Dr Biddulph said temperatures achieved over the past week, in the high 20s and low 30s throughout the Wheatbelt, would intensify the damage to crops from the successive frosts.

"Heat stress exasperates frost damage, particularly stem damage, because any frost damage on the stem restricts the plant's ability to shift water and sugar up to the flowering grain," he said.

"The hot northerly and easterly winds we have been seeing over the past week across the grain growing areas cause damage themselves and will further exacerbate the damage, obviously depending on what stage the crop development is at."

Heat by itself can lead to sterility similar to frost at flowering stage and can reduce grain size.

Dr Biddulph said the wheat variety Wyalkatchem had been identified as the most susceptible commonly grown variety to frost.

He said GRDC National Frost Initiative frost rating wheat variety guide would be available for release next year.

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