The ANZ said its commodity price index fell 4 per cent in April - returning the series to where it was eight months ago - driven mostly by falls in dairy prices.
Annual growth in the index dropped to minus 2.8 per cent, the first negative rate of change since February 2013, ANZ said.
Seven commodity prices weakened in the month of April, six increased, and four remained unchanged.
Four commodities recorded double-digit price declines in April. "The fall was dairy centric, with dairy products accounting for three of the four largest falls," ANZ said in a statement.
The price of butter and pelts led the decline, both fell 14 per cent in April. This was followed by decreases in milk powder prices - skim milk prices dropped 12 per cent and whole milk powder prices fell 10 per cent.
Cheese prices decreased by 4 per cent and beef prices eased by 1 per cent.
But ANZ said it was not all one way traffic, with six commodities posting a lift in prices.
Aluminium prices recorded the largest increase, lifting 6 per cent, followed by sheepmeat prices which rose 3 per cent.
The prices of wood pulp, seafood, and wool all increased 1 per cent, and lumber prices nudged up a quarter of one per cent. The prices of logs, kiwifruit, apples and venison were unchanged in the month.
The New Zealand dollar strengthened across all our major trading partners, with the exception of the Australian dollar.
This exacerbated the fall in commodity prices when converted in the local currency, resulting in a 5 per cent fall in the ANZ NZD Commodity Price Index for April, which was at a 13-month low.