The renewed anxiety adds to pressure on the European Commission to forge a deal this year to help ensure that EU biofuels do not clash with food production or the environment.
Such an agreement would remove some of the uncertainty that has hung over the multi-billion-euro bioenergy industry during years of debate.
The UN Food and Agriculture Organization last week called for a suspension of US ethanol quotas as a response to the impact of the worst American drought in more than half a century on corn supplies and prices.
Ahead of a US election, immediate change is unlikely. But the debate highlights concerns that EU goals also stoke commodity volatility because they exaggerate inelasticity of demand.
"The US situation should be a warning for the EU that our inflexible biofuel mandate can lead to food price volatilities, especially as we are currently converting 65% of our vegetable oils into biodiesel," said Nusa Urbancic, programme manager at campaign group Transport and Environment.
Scepticism about carbon targets
In the EU, more so than in the United States, biofuels are part of the strategy to lower carbon emissions. Urbancic and many other campaigners doubt it achieves that.
"Science has also shown that biodiesel can be worse for the climate than conventional oil, once indirect impacts on forests and peatlands are included," she said.
Action plans drawn up by EU member states predict that bioenergy, including biomass for power generation and biofuel for transport, will provide more than 50% of the EU share of renewable energy as part of 2020 climate goals.
The European Commission has said it opposes anything that inflates food prices. What it hasn't worked out is how to ensure that its own biofuel policy does not have that distorting effect.
EU sources have said the Commission will attempt to get agreement before the end of the year on how to measure ILUC.
The aim is to clarify the impact of biofuel policies on displacing food crops or driving unwelcome environmental change.
For now, Energy Commissioner Günther Oettinger has opposed raising a target of deriving 10% of transport fuel from biofuels, as part of an overall goal to get 20% of energy from renewables by 2020.