Publicação on-line; 22 ref.; 5 tables; 1 illus.; Summary (En)

ABSTRACT
Background: Weed interference is a major limiting factor for
economically viable soybean production. Appropriate timing of weed
management would enable farmers to make more efficient use of
resources for weed management.
Objective: The objective of this study was to determine the critical period
for weed competition and appropriate timing of weed management for
optimum yield of soybean.
Methods: The treatments consisted of periods of weed infestation and
weed removal for the first 14, 28, 42 and 56 days after sowing (DAS), and
till harvest in a randomized complete block design with three replications
in 2016 and 2017.
Results: Soybean yields in both years ranged from 914-945 kg ha-1 with
no weed control to 1,984-2,127 kg ha-1 in the weed-free plots; a yield loss
of 53-56%. Weed infestation for the first 14 DAS had no detrimental effect
on growth and yield of soybean provided the weeds were subsequently
removed. Increasing period of weed interference from 14 to 42 DAS
resulted in a steady decline in growth and yield of soybean. Yield losses
equivalent of 32-37 kg ha-1 resulted for each day that weed control was
delayed between 14 and 42 DAS. Subsequent weed control after 42 DAS
did not improve growth and yield significantly, nor obviate yield
depression of the crop compared to crop weed-infested till harvest.
Conclusions: Results indicated that the critical period of weed
competition in soybean was between 14 and 42 DAS. Hence soybean
should be maintained weed-free during this period to avoid high yield
loss.

Keywords:
critical period Glycine max (L.) Merrill
manual weeding
weed control
weed infestation