The ANZ Commodity Price Index fell 4.2 per cent to a 21-month low in May as rises in the price of apples and kiwifruit failed to offset declines in the price of wool and dairy products.
The index, at 260.8, has fallen 12 of the past 13 months. It is 18 per cent below its peak, while dairy prices are 28 per cent below their peak.
"The ANZ Commodity Price Index took another step down in May, with eleven commodities registering weaker prices and only four price increases being measured," ANZ economist Steve Edwards said in his report.
An 11 per cent fall in the price of wool to the lowest level since September 2010 was the largest monthly decline in May.
Weaker dairy prices were also a feature. There was a 12 per cent decline in the price of butter, a 9 per cent fall in the price of whole milk powder, an 8 per cent fall in the price of skim milk powder and a 4 per cent fall in the price of casein. The price of cheese fell 2 per cent.
Sheep meat prices dropped 6 per cent, while the price of aluminium eased 2 per cent.
Exports of the new season's braeburn crop helped lift apple prices 12 per cent and kiwifruit prices lifted 7 per cent as the export season geared up. Sawn timber prices increased 1 per cent.
The value of the New Zealand dollar declined in May by more than the fall in commodity prices so the ANZ NZ dollar Commodity Price Index lifted by 0.8 per cent.