Allelopathic inhibition typically results from the combined action of a group of allelochemicals which, collectively, interfere with several physiological processes. The objectives of this paper are to summarize research that illustrates the joint action of allelochemicals, and to provide evidence that both the amount and detrimental action of these compounds depends on the extent of associated abiotic and biotic stresses. Allelopathy is strongly coupled with other stresses of the crop environment, including insects and disease, temperature extremes, nutrient and moisture variables, radiation, and herbicides. These stress conditions often enhance allelochemical production, thus increasing the potential for allelopathic interference. In the paradigm of interactions, the data indicate that crops are more sensitive to allelopathy when moisture, temperature, or nutrient conditions are less than optimal. For example, the inhibition threshold concentration for ferulic acid to affect seedling growth was reduced with even minor moisture stress (Ψ = − 0.15 MPa) or a growth temperature at the higher end of the normal range for a species. Under greenhouse conditions, additive inhibition resulted from the joint action of ferulic acid with low levels of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], atrazine [6-chloro-N-ethyI-N’-(1-methylethyl)-l,3,5-triazine-2,4-diamine], or trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine]. Interactions of multiple stresses in crop environments will determine the relative impact of allelopathy. Alldopathystress interactions also have implications for herbicide and residue management slrategies, crop rotations, biological control measures, and tillage practices that can contribute to a more sustainable agriculture.
Presented at a symposium, Allelopathy in Cropping Systems (jointly sponsored by Div. C-3, C-2, S-6, and S-8), at the ASA-CSSA-SSSA annual meetings in Seattle, WA, 14 Nov. 1994.