We investigated the phytotoxicity of desert cotton (Aerva javanica) extracts on wild oat and wheat. Aqueous extracts from A. javanica roots, leaves and inflorescences collected from Jeddah and Al-Baha regions, Saudi Arabia were used. Generally, the allelopathic potential of water extracts of A. javanica collected from Jeddah were more in inhibitory to wild oat germination and seedlings growth than those from Al-Baha. In both regions, root extracts were inhibitory to wild oat followed by leaves and inflorescences extracts. All test aqueous extracts of both regions did not inhibit the wheat germination or seedlings growth.Whreas, the wild oat germination was reduced by root extracts 58.62 %, 28.62 % leaves extracts : 32.72 %, 17.72 % and inflorescences extract 28.11 %, 12.13 % by in plants samples collected from Jeddah and Al-Baha, respectively. Wild oat radical length was inhibited by root extracts 53.27 %, 32.84 % leaves 42.35 %, 9.63 % and inflorescences extracts 22.64 %, 16.75 % in case of Jeddah and Al-Baha plants, respectively. In pot culture experiment, all treatments markedly reduced the plant dry weight and soluble carbohydrates, proteins and free amino acids contents in wild oat. The differences in the allelopathic potentials of studied A. javanica extracts were related to the qualitative variations in their phytochemicals constituents. Our results showed that A. javanica extracts could be safely used to control wild oat growth in wheat fields after more detsaled research..

Abstract

This glasshouse study aimed to determine the herbicidal activity of allelochemicals 2,4-di-tert-butylphenol (2,4-DTBP) on test weeds (Asystasia gangetica, Eleusine indica, Leptochloa chinensis and Oldenlandia verticillata) and to find the tolerance of test crops (Brassica rapa, Oryza sativa, Zea mays) to 2,4-DTBP. The 2,4-DTBP applied at 7 kg ai/ha inhibited the weeds seedling growth by 15-40 % only, showing its poor post emergence herbicidal activity. In contrast, soil bioassay confirmed pre-emergence herbicidal activity of 2,4-DTBP that reduced the seedling growth of weeds (L. chinensis, E. indica and O. verticillata) by 50- 80 % at 2.5 kg ai/ha but A. gangetica was tolerant to 2,4-DTBP even at 5 kg ai/ha. Crop tolerance test revealed that Zea mays was tolerant to 2,4-DTBP. In contrast, root lengths of transplanted Brassica rapa seedlings and Oryza sativa seedlings were reduced by 10- 15 % at 2,4-DTBP doses of 1.25 to 5 kg ai/ha, 14 days after treatment. However, these two crops seedlings became tolerant to 2,4-DTBP at 5 kg ai/ha, when applied 4 days after transplanting. Thus 2,4-DTBP may be developed as novel pre-emergence natural herbicide, without injuring the crops depending on their growth stages and crop species.