It is now essential to reduce the negative impacts of weed management and especially herbicide use. Weed-suppressive crop
species/varieties hold promise for integrated and sustainable weed regulation. Competition for resources and allelopathy are
the two main underlying mechanisms. Unlike competition, which is well studied and established, allelopathy by living crops
remains a contentious mechanism. A major difficulty to demonstrate the effects of allelopathy in the field is to dissociate them
from those of competition. Here, we systematically and quantitatively review the literature, searching for field-based evidence
of the role of allelopathy (by root exudation of living crops) in weed regulation, independently of competition, focusing on
studies comparing different varieties of a given crop species. Our critical literature analysis also aims to identify weaknesses
and strengths in methodology, providing insights on optimal experimental designs and avenues for future research. Our main
conclusions are: (1) in most articles, the role of crop competition is disregarded or not exhaustively studied. Consequently,
contrary to authors’ conclusions, it cannot be determined whether weed regulation is due to allelopathy and/or to competition.
(2) Few articles provided convincing evidence of the presence/absence of allelopathy in the field. (3) To further investigate
allelopathy in the field we recommend to (i) finely characterize crop competition by measuring traits in the field, (ii) assess
crop allelopathic potential with complementary experiments in controlled conditions or by quantifying allelochemicals in
the field, and (iii) quantify the contribution of each studied trait/mechanism in explaining weed regulation in the field with
multiple regression models. In conclusion, the consistent use of the suggested guidelines, as well as alternative approaches
(e.g., creation of varieties with deactivated allelopathic functions, development of process-based simulation models), may
provide a basis for quantifying the role of allelopathy in the field and, subsequently, for designing weed management strategies
promoting weed biological regulation.