Effect of soybean spatial arrangement and glyphosate dose on Anoda cristata demography

Without herbicides, biomass and seed production per unit area was lower in narrow-row compared to wide-row soybean but no differences in biomass production of the weed were observed between narrow spacings with high and low densities. In all planting patterns, weed biomass and seed production decreased progressively from the first to the third weed emergence. The use of half of the recommended glyphosate dose relative to treatments without glyphosate application reduced biomass and seed production in all planting patterns, but this reduction was greatest in narrow-row soybean. Without glyphosate, in both the row spacings, flowering and seed production occurred earlier for the first relative to the second weed emergence. With the application of half of the recommended dose, flowering occurred only in the first weed emergence and both flowering and seed production were observed first in wide-row relative to narrow-row soybean. The recommended glyphosate dose controlled both the first and the second emergence, but the third emergence was not affected and remained in the vegetative stage till crop harvest. Without glyphosate and using half of the recommended glyphosate dose, reducing soybean row spacing is a more important factor than increasing crop density in reducing A. cristata populations.