Biofuels are likely to cause significant weed problems because the attributes of an ideal biofuel species ' including rapid growth with minimal fertiliser and water needs ' match those of typical weeds, and because cultivation will be on a vast scale. The valued biofuel giant reed is one of the world's worst invaders. To reduce weed risk, biofuels could be cultivated under voluntary guidelines or legislative controls. But self-regulation has a poor track record, and legislative controls would impose a cost on society because biofuels are high-volume low-value crops with limited profit margins to fund weed management. Extreme weather events can exceed landholder capacity for control of escapes. Restricting candidate species to those with low weed risk is advisable, and many native species would offer safe potential.