Allelopathic effects of horseweed on germination and growth of seven common weeds of Southeastern US

Authors: GHOSH, RAKESH - Auburn University; Price, Andrew; MAITY, ANIRUDDHA - Auburn University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Erigeron canadensis L. (2n= 18, family: Asteraceae) or horseweed (HW) is known as one out of ten most troublesome and most common weeds in 12 categories of broadleaf crops, fruits and vegetables, and present in 2,540 counties across the US. Wide phenotypic plasticity coupled with adaptive morphological traits and allelopathy might have resulted in its rapid spread and extensive presence across the US presumably by altering the composition of local plant community. This study for the first time revealed the allelopathic effect of HW leaf aqueous extract (10%) on seed germination and seedling growth of seven commonly growing weeds including Palmer amaranth, smooth pigweed, pricklysida, pitted morningglory and lambsquarters which are native to North America, and non-native curlydock and barnyardgrass. HW aqueous extract significantly (p<0.05) reduced the seed germination and seedling growth of smooth pigweed, palmer amaranth, curlydock and lambsquarters, and showed nonsignificant impacts on pitted morningglory, pricklysida and barnyardgrass. These results establish a solid foundation for understanding the mechanisms driving the successful invasion of horseweed in native range and provide a valuable theoretical framework for early-warning systems assessing ecological risk. The current study, utilizing a petri-dish bioassay, explains HW’s invasive potential on the succession of commonly occurring native and non-native weed species in the southeastern United States.

Technical Abstract: Erigeron canadensis L. (2n= 18, family: Asteraceae) or horseweed (HW) is known as one out of ten most troublesome and most common weeds in 12 categories of broadleaf crops, fruits and vegetables, and present in 2,540 counties across the US. Wide phenotypic plasticity coupled with adaptive morphological traits and allelopathy might have resulted in its rapid spread and extensive presence across the US presumably by altering the composition of local plant community. This study for the first time revealed the allelopathic effect of HW leaf aqueous extract (10%) on seed germination and seedling growth of seven commonly growing weeds including Palmer amaranth (Amaranthus palmeri), smooth pigweed (Amaranthus hybridus), pricklysida (Sida spinosa L.), pitted morningglory (Ipomoea lacunose L.) and lambsquarters (Chenopodium album L.) which are native to North America, and non-native curlydock (Rumex crispus L.) and barnyardgrass (Echinochloa crusgalli (L.). HW aqueous extract significantly (p<0.05) reduced the seed germination and seedling growth of smooth pigweed, palmer amaranth, curlydock and lambsquarters, and showed nonsignificant impacts on pitted morningglory, pricklysida and barnyardgrass. Based on synthetical allelopathic effects (SE<0), the order of inhibition from high to low was smooth pigweed (-0.58)< curlydock (-0.46) = palmer amaranth (-0.42) < pricklysida (-0.26) < lambsquarters (-0.19) < pitted morningglory (-0.03) = barnyard grass (0.01). From liquid chromatography of the HW aqueous extract, a total of 39 compounds including piperidine, choline, 4-hydroxybenzaldehyde, acetonecyanohydrin, along with several phenolic acids like gallic acid, 2-furoic acid, genistein, gentisic acid etc. with previously known allelopathic potential were identified. These results establish a solid foundation for understanding the mechanisms driving the successful invasion of horseweed in native range and provide a valuable theoretical framework for early-warning systems assessing ecological risk. The current study, utilizing a petri-dish bioassay, explains HW’s invasive potential on the succession of commonly occurring native and non-native weed species in the southeastern United States.