Sensitivity of yellow foxtail (Setaria glauca L.) and barnyardgrass (Echinochloa crus-galli L.) to aqueous extracts or dry biomass of cover crops

Pyroligneous acids from biomass charcoal by-product as a potential non-selective bioherbicide for organic farming: its chemical components, greenhouse phytotoxicity and field efficacy

Effective and environmentally friendly herbicides are urgently needed to meet consumer demand for organic products. To evaluate the weed control effect of four pyroligneous acid (PAs) mixtures, the byproducts of bamboo/wood/straw vinegar, two herbicide discovery tests were done: (1) the greenhouse tests by using four indicative plants: wheat (Triticum sativa), radish (Raphanus sativus), cucumber (Cucumus sativus), and Echinochloa crusgalli (L.) Beauv; (2) Field trials with four weeds: E. crusgalli, Eleusine indica (L.) Gaertn, Alternanthera philoxeroides (Mart.) Griseb, and Conyza canadensis (L.) Cronq. Greenhouse tests showed that the efficacy of PAs and acetic acid (AA) to control four test plants increased with the increasing of PAs concentration. The inhibition rates of four tested PAs (FBV (0.6-9.2% AA + (0.3-5.0% tar), HWV (0.2-1.8% AA + 0.3-4.3% tar), ASV (0.5-8.7% AA + 0.4-7.0% tar), and CWV (0.7-5.3% AA + 0.5-7.5% tar) gave inhibition rates of 56 ± 4-97 ± 2%, 21 ± 2-90 ± 6%, 29 ± 3-98 ± 5%, and 44 ± 6-86 ± 2%, respectively, and the field effects of PAs against four weeds were enhanced with the increasing of concentrations and time after spraying (1 to 14 days). Their control effects against E. crusgalli, E. indica, A. philoxeroides, and C. canadensis were 4 ± 1-93 ± 4%, 7 ± 3-90 ± 3%, 32 ± 2-95 ± 3%, and 31 ± 5-96 ± 4%, respectively. The mixed effect of the four PAs was higher than the same dose of AA. These results will help to determine the potential of PAs to be developed as non-selective herbicides to control weeds in organic farming.

Selected Phenolic Acids Inhibit the Initial Growth of Ambrosia artemisiifolia L

This study aimed to investigate whether different doses of specific phenolic acids (chlorogenic acid, caffeic acid, ferulic acid, gallic acid, protocatechuic acid, p-hydroxybenzoic acid, syringic acid, vanillic acid, and p-coumaric acid), alone or in combination, can inhibit the early growth of the common ragweed (Ambrosia artemisiifolia L., Asterales: Asteraceae). A seed bioassay was performed in Petri dishes and placed in a climate chamber to assess the effects of five dose levels of phenolic acids to radicle and shoot length, as well seedling biomass of A. artemisiifolia. The lowest dose of phenolic acid corresponded to the natural phenolic acid concentration previously reported in dry plant tissue samples from Brassicaceae cover crop plants. Results show that the inhibition of the early growth of A. artemisiifolia depends strongly on phenolic acid. Across different treatments, high doses of phenolic acids significantly shortened shoots and radicles, as well as reduced seedling biomass. Treating seeds with ferulic acid alone, vanillic acid alone, p-hydroxybenzoic acid alone, or a mixture of all phenolic acids significantly reduced all early growth parameters. The estimated effective dose for the 50% inhibition (ED50) of radicle growth in A. artemisiifolia seedlings was 368.39 ± 59.85 × 10−8 mol with ferulic acid, 135.41 ± 17.65 × 10−8 mol with p-coumaric acid, 810.36 ± 134.15 × 10−8 mol with p-hydroxybenzoic acid, and 160.11 ± 12.30 × 10−8 mol with the combination of all phenolic acids.

Inhibitory Effects of Brassicaceae Cover Crop on Ambrosia artemisiifolia Germination and Early Growth

Several cover crops (CCs) exert allelopathic effects that suppress weed growth. The aim of the present study was to evaluate the effects of aqueous extracts containing different concentrations [0, 0.5, 1, 2.5, 5, 7.5 and 10% (w/v)] of Brassicaceae CCs (Sinapis alba, Raphanus sativus, Camellina sativa) and of the CCs Fagopyrum esculentum and Guizotia abyssinica on germination and early growth of Ambrosia artemisiifolia L. The allelopathic effects were species and concentration-dependent. C. sativa, for example, caused the greatest potential to inhibit germination, shoot, radicle length and fresh seedling weight, whereas S. alba and R. sativus inhibited germination and early growth of A. artemisiifolia only at concentrations ≥7.5%. In contrast, no inhibition was observed when aqueous extracts of F. escultneum and G. abyssinica were added at any of tested concentration. Liquid chromatography-tandem mass spectrometry detected 15 phenolic compounds in Brassicaceae CCs with the highest content (µg/g) of vanillin (48.8), chlorogenic acid (1057), vanilic acid (79), caffeic acid (102.5) and syringic acid (27.3) in C. sativa. Our results suggest that C. sativa is the most allelopathic CCs and that the fruits of C. sativa are the plant organs richest in allelochemicals.