beeThis review provides an overview on the most common rice weed species of the world. It shows that a
few generalists have established in rice independent from sites, crop management systems, and local
climatic conditions. Cosmopolitan weeds are even constant elements where rice cultivation started just a
century ago. Local differences may be explained by cultivation methods, growing seasons, or special
weed management. Some general changes in weed spectra have been observed globally in recent years.
Weedy rice (Oryza sativa L.) and herbicide resistance have become general global problems within the
last decades. Some global key weed genera such as Echinochloa, Cyperus, Scirpus, or Fimbristylis species
are, however, still dominating rice fields despite the decade long use of well performing herbicides. On
the other side, general species shifts as a result of resistance have not been observed yet. Leptochloa
species started to become major problems in Asia in the end of the last century and now in Europe also.
Several modern herbicides allow the control of perennial weeds, such as Cyperus rotundus L. or Eleocharis
kuroguwai Ohwi which makes them no longer serious threats. Some genera in rice such as Echinochloa
and Oryza (weedy rice) are characterized by an enormous germplasm variability which makes species
definitions difficult. The fact that weeds in rice have to adapt to wet or aquatic conditions reduces the
biodiversity range in comparison to other arable crops. Water management has a considerable impact on
weed spectra. The increase of rice acreages with reduced irrigation may end up in higher weed infestations.
Long term results of weed surveys in rice as they exist for other crops are, however, not
available. This makes predictions on biodiversity changes in this crop quite difficult.