Suitability of High Doses of Phenolic Acids for Controlling Corchorus Olitorius and Phalaris Minor Weeds

The herbicidal potential of nine phenolic acids including p-hydroxybenzoic acid, protocatechuic, syringic, vanillic, gallic, salicylic, ferulic, p-coumaric and caffeic acid were evaluated against Corchorus olitorius and Phalaris minor weeds at the concentrations of 5, 10 and 20 mM. The effectiveness of phenolic acids on germination depended on target seed, specific phenolic acid and concentration. The inhibitory effects varied between the two tested seeds, and P. minor was the more sensitive. With few exceptions, phenolic acids at all tested doses did not inhibit seed germination of C. olitorius, but the acids caused great inhibition effects on germination of P. minor. Salicylic acid nearly had a complete inhibition effect on germination of tested seeds when used at 20 mM. P-hydroxybenzoic, protocatechuic, salicylic, vanillic and ferulic acids appeared great inhibition effects on germination of P. minor and nearly had complete inhibition effects when used at high dose. In a greenhouse trial, we found that application of phenolic acids at 5–20 mM did not produce any significant effect on growth on 5‑weeks-old C. olitorius or P. minor plants, after seven days from treatments. The study concluded that phenolic acids had diverse activities on germination and growth of C. olitorius or P. minor weeds.