ZERO and sub-zero temperatures recorded in the Great Southern and central and eastern wheatbelt on October 10 were unlikely to have caused significant damage to cereal crops, according to the Agriculture Department.
On October 10 temperatures fell to -.03 degrees at Merredin for four hours, -1C at Meckering and Northam for four hours and -.04 at Wongan Hills for five hours. At Wickepin and Lake King temperatures dropped to -.02 and -.07 for seven hours.
Agriculture Department research officer Ian Foster said the impact of the October 10 frost would have been reduced by soil temperatures 2-7 degrees warmer than at the time of the September 10 frost, which caused significant damage.
The crops on October 10 were also at a different stage of development and the minimum temperatures were not as low or prolonged as the frost on September 10, which caused most damage to crops in the Merredin district.
"Quite a few of the crops have passed flowering but you can still get some damage to the heads," he said.
Mr Foster said there was more variability of flowering times this year which made it difficult to make a statement on frost damage before harvest when the full impact would be known.
Merredin Dryland Research Institute principal researcher Doug Abrecht expected minimum damage in his area from the October 10 frost but said damage was showing from previous frosts, including the big September 10 freeze.
Mr Abrecht said there was stem and flower damage to cereal crops from frost while earlier planted crops could have both stem and grain frost damage.
"The impact has been patchy and some areas have lost a lot of yield," he said.
"Most of the damage is through flower frost and earlier stem damage."
He said the impact of the September 10 frost on flowering wheat and barley would account for most of the estimated 400,000t reduction in the harvest from 13.2mt to 12.8mt.
Mr Abrecht said stem damage would lead to shrivelled up grain and more screenings while flower damage would reduce yield but provide good quality grain due to a compensatory effect where undamaged heads received more nutrients.
Agriculture Department Corrigin farming systems and development officer Alison Slade said most farms in the area would have received some head frost damage to wheat and barley crops this season, but damage was also patchy.
Ms Slade said the damage ranged from a few paddocks on some farms to 70-80pc of crops on others.
"Its mainly east of Corrigin town and up towards Babakin," she said.