This work aimed to evaluate the period before weed interference in soybeans, var. Coodetec 202, in a no-till area in Maringá, PR, using two-fold checks. The main weed in this area after crop installation was Bidens pilosa, averaging from 50 to70 plants m-2. Other minor weeds were Euphorbia heterophylla, Brachiaria plantaginea, Sida rhombifolia, Acanthospermum hispidum, Commelina benghalensis, Cenchrus echinatus and Desmodium tortuosum. The crop was kept free of weed interference during initial periods after crop emergence (7, 10, 14, 21, 28, 35, 42, 49 days after emergence and for the whole the crop cycle 118 days). After each consortium period, weeds were manually eliminated, as well as the new weeds thereafter, until crop harvest. Two additional standards with pre- and post-emergence herbicide treatments were also evaluated. For weed interference periods e > 14 days, there was a significant soybean yield decrease. Using two-fold checks, it was established that the period before weed interference must be10 days after soybean emergence. Yield losses ranged from 16.8% (weed interference for 14 days after crop emergence) to 28.03% (interference for the entire cycle). Yield loss estimate by delaying weed control up to 18 days after crop emergence (timing for post-emergence control) was 452 kg ha-1 (16,74%).
Bidens pilosa; competition; herbicide
