There is limited information about the critical period of weed interference (CPWI) in quinoa (
Chenopodium quinoa
Willd.) and the effect produced by the weed-crop interaction in secondary metabolite accumulation. The objective of the present study was to determine the CPWI and its effect on total polyphenol content in quinoa. The experiments were conducted during two consecutive seasons using a randomized complete block design with 16 treatments consisting of 8 weed growth periods and 8 weed-free growth periods in which weed population and biomass were evaluated; productive parameters, yield components, and total polyphenols were determined in the quinoa crop. Grain number per plant affected yield because of weed interference (P < 0.05), which decreased from 4312 to 162 grains plant
-1 in weed growth periods and increased from 181 to 5110 grains plant
-1 in weed-free growth periods. Total polyphenol content was affected by stress from weed interference (P < 0.05), which increased from 2.2 gallic acid equivalents (GAE) g
-1 to 3.6 mg GAE g
-1 in weed growth periods and decreased from 3.6 GAE g
-1 to 1.9 mg GAE g
-1 in weed-free growth periods, while the population remained constant (P > 0.05). The CPWI was determined between the phenological stages of two true leaves to flowering; therefore, the quinoa crop must remain weed-free between these two phenological stages to rule out production losses
greater than 5%.
