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Agronomy Journal Abstract -

Weed Population Dynamics and Weed Control in the Peruvian Amazon


This article in AJ

  1. Vol. 82 No. 1, p. 102-112
    Received: Apr 18, 1989

    * Corresponding author(s):
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  1. Jane Mt. Pleasant ,
  2. R. E. McCollum and
  3. H. D. Coble
  1. D ep. Agronomy, Cornell Univ., Ithaca, NY 14853
    D ep. Soil Sci., North Carolina State Univ.
    D ep. Crop Sci., N.C. State Univ., Raleigh, NC 27695



In traditional slush-and-burn agriculture, forest fallow is a primary agent in weed control. Stable continuous-cropping systems could be expected to require a comprehensive program of weed management, probably including the use of herbicides. Weed control measures in a sequence of rice (Oryza sativa L.)-corn (Zea mays L.)-soybean (Glycine max L.)-rice-corn-soybean were studied for 2 yr in Yurimaguas, Peru, with the following objectives to: (i) identify weed species resistant to the herbicide program in a continuous cropping system, and (ii) develop effective weed management practices for intensively managed cropping systems in the humid tropics. First-crop weeds were 60% grass, 25% sedges, and 15% broadleaf weeds. The grass was composed of two species: large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass (Eleusine indica (L.) Gaertn]. Sixth-crop weed population was 80% grass, 13% broadleafs and 7% spreading dayflower (Commelina diffusa Burm. f.); and itchgrass (Rottboelia exaltata L.f.) comprised 85% of the grasses. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide] controlled crabgrass, goosegrass, and most broadleafs in corn and soybean; but it did not control itchgrass. Metolachlor alone resulted in a weed population that was 97% itchgrass in the sixth crop. Sethoxydim {2-[(1-ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-l-one}-plus bentazon [3-(1-methylethyl)-(1.H)-2,1,3-benzothiadiazin-4(3H)-one 2.2-dioxide] on soybean controlled grasses including itchgrass, but broadleaf weeds and dayflower increased. Propanil [N-(3,4-dichlorophenyl) propanamide]-plus-oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethyl)-1,3,4-oxadiazol-2-(3H)-one} on rice resulted in a mixed grass population. Rice was more vulnerable to weed pressure than either corn or soybean and appears inappropriate for this high-input rotation because of the high cost of weed control.

Paper no. 11523 of the Journal Series of the North Carolina Agric. Res. Serv. Contribution of the TropSoil Program conducted jointly with the Institute Nacional de Investigacion Agropecuaria y Agronindustrial (INNIAA) of Peru and supported by the U.S. Agency for International Development. Part of a thesis presented to North Carolina State Univ. by the senior author in partial fulfillment with the Ph.D. requirement.

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