Monday, September 24, 2012

Frosts another spicy ingredient for the yield forecasting cauldron


A large high pressure system has been moving in from the west over the last few days, bringing mostly clear nights and light winds. These conditions mixed with a cool air mass from last week's wintery blast (it was even reported on Canadian news!) has lead to the ’perfect storm’ for the recent frosty conditions.  Not many growing regions have escape some form of extreme cold weather this winter, slowing plant growth. Concerns have been further compounded with frost’s at the worst possible time throughout WA, SA Mallee, Vic, central/northern NSW and southern QLD.

With scattered sowing dates and resulting level of maturity it is difficult to get the full impact of these frosts. The SA Mallee and the Western District of Victoria (where frost can pose serious yield penalties up to Melbourne Cup time), have had frosts last week and again yesterday (Sunday). There is definitely crop at risk in all categories. Temperatures below 2°C during flowering can cause yield reductions of about 20 to 40% in wheat. And temperatures below 0°C during grain filling cause additional losses of about 20%. However depending on the individual paddock it can be a total wipeout. A few of these incidents have been commented on by growers calling the office, however they have not been the norm. key growing regions of  NSW,  have experienced decile 1 temperatures last month. Apparently Junee has had  had 45 frosts since late June.!

WA, how does it compare to 2010? With the state accounting for 40% of national production, and the percentage of wheat exports ranging between 30 to 75%, it is only natural that every drop of rain (or lack thereof) is scrutinized closely.  Parallels have been made to 2010, a year that was characterized by a late sowing, and dry spring (similar to 2012).  That year an estimated 5mmt wheat crop was produced on GSR on 171mm, with only 20mm falling in Sept/Oct. The Esperance region was the only shining light producing 850kt or 17% of the state crop (usually 10%).

This year however there is no real good patches, albeit overall severity isn't as severe. The biggest difference has been last months rainfall, with 34mm falling, compared to 14mm in 2010. History is littered with examples of crops coming back from the dead in timely rains like these. Of the 70 weather stations in the ‘Upper Great Southern” region. September was the first month of above average rainfall (36mm) since February. So crops will need a miracle if they are to stage any meaningful recovery. The Australian Crop Forecasters wheat yield model continues to favour a strong downward at 4.9mmt, 1mmt less then our current forecast.

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