Plant Growth Response to Several Allelopathic Chemicals

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Abstract
Salicylic acid,p-hydroxybenzoic acid, caffeine, hydroquinone, and umbelliferone were evaluated in the greenhouse for their effects on shoot dry-weight accumulation of several crop and weed species. With the exception of caffeine, all the chemicals reduced shoot growth in oats (Avena sativaL. ‘Goodfield’). Chemicals applied preplant incorporated, preemergence, or postemergence were effective, depending upon the rate of chemical. When applied preplant incorporated at rates as high as 56.0 kg/ha, most of the chemicals reduced growth of corn (Zea maysL. ‘B73 × Mo17′), soybean [Glycine max(L.) Merr. ‘Corsoy’], velvetleaf (Abutilon theophrastiMedic.), redroot pigweed (Amaranthus retroflexusL.), and wild proso millet (Panicum miliaceumL.). Exceptions were caffeine on corn and soybean and hydroquinone on soybean. At 11.2 kg/ha the chemicals inhibited the weed species more than the crop species. Postemergence applications of caffeine and hydroquinone inhibited growth of the weed species more than the crop species. Hydroquinone at 1.1 kg/ha inhibited redroot pigweed, but rates as high as 11.2 kg/ha did not inhibit soybean. These experiments show that growth of agronomically important crops and weeds can be inhibited differentially by allelopathic chemicals.