Export commodity prices fell almost 1 per cent in June, the fourth monthly drop in a row.
Apple prices took the biggest tumble, but aluminium prices rose.
The ANZ commodity price index is down 6.7 per cent from the peak in February in world price terms for a basket of New Zealand's top exports.
Including a range of products from dairy to aluminium, the index is at its lowest level in 15 months.
Dairy and forestry product prices have fallen heavily in recent months.
Other sectors are improving, with aluminium up to its best levels in 14 months.
In world price terms, meat prices were the best for 14 years, ANZ said.
The biggest fall in June was for apples, down 6 per cent on the previous month.
ANZ said that was typical for the time of year as the northern hemisphere export season picked up.
Logs were down 5 per cent in the month, the ANZ report showed.
Recent forestry industry reports suggest log prices have slumped about 20 per cent in the past couple of months as demand slowed in the key China market.
Whole and skim milk powder prices were down 3 per cent in the month, ANZ said.
The ANZ report was for June before yesterday's GlobalDairyTrade auction, which saw prices slide another 4.9 per cent.
The auction platform is owned by Fonterra, which accounts for about 90 per cent of the product sold at the auctions.
The report showed aluminium prices jumping 5 per cent in June, the biggest rise for any commodity.
Kiwifruit and wool prices were up 3 per cent each, and beef was up 2 per cent.
Seafood prices are at all-time highs in world price terms.
ANZ said the New Zealand dollar rose slightly in June, taking the New Zealand index down 1.1 per cent in the month.
Prices are 13.6 per cent below the March 2011 peak in New Zealand dollar terms.