Abstract: 【Objective】Flixweed (Descurainia sophia) is the most serious broad-leaved weed in main areas of winter wheat production in China, and it seriously threatens winter wheat production. The objective of this study is to determine the D. sophia dynamics of emergence, plant height, fresh weight and its competitive effect on yield components of wheat. 【Method】 The dynamics of emergence, plant height and fresh weight of D. sophia were surveyed by fixed quadrat sampling and random sampling in wheat field with severe D. sophia infestation in Ji’nan from 2013 to 2014. Shallow rotary tillage was implemented in experimental plot with maize straw giving back before wheat sowing. In order to compare the effect of different D. sophia densities on wheat yield, three wheat planting densities were set as 67.5, 135.0, and 202.5 kg·hm^-2, each wheat planting densities set with different D. sophia densities as 0, 10, 20, 40, 60, 80, 160, 320, 640, and 1 280 plants/m². D. sophia densities were based on artificial inoculation, and three final thinning of seedlings were made before winter, early spring, and revival stage. Excel graphing was conducted to analyze the cause of yield loss caused by D. sophia.【Result】The peak of D. sophia seedling emergence appeared after wheat seeding one week to mid-November, the weekly average temperature at 13.5-14.8℃. The amount of seedling emergence before winter accounted for 96.7% of the total annual emergence. In late March, the weekly average temperature raised above 8.0℃, D. sophia seedling began to grow rapidly. Plant height of D. sophia was higher than wheat after early April. In mid-May, D. sophia plant height reached maximum 115.6 cm, and 43.4 cm higher than wheat. The fresh weight of D. sophia and wheat changed slowly at overwintering stage. Fresh weight of D. sophia increased rapidly after April, achieved the maximum 50.2 g in early May, which was four folds of wheat. The effect of D. sophia on wheat yield was primarily through inhibiting the effective ears and grain number per ear of wheat. It had no significant effect on 1 000-seed weight. Wheat spikes were from 4.29 to 0.28 million/hm², reduced by 93.5%, when the D. sophia plant rose from 0 to 640 plants/m² in the plot with 67.5 kg·hm^-2 wheat sowing amount. Wheat spikes were from 5.49 to 1.88 million/hm², reduced by 65.8%, when the D. sophia plant rose from 0 to 640 plants/m² in the plot with 135.0 kg·hm^-2 wheat sowing amount. Wheat spikes were from 6.69 to 3.22 million/hm², reduced by 52.0%, when the D. sophia plant rose from 0 to 320 plants/m² in the plot with 202.5 kg·hm^-2 wheat sowing amount. The loss rate of wheat was 84.7%, 71.9%, and 64.9% when the D. sophia density was at 320 plants/m² in the three wheat planting densities. The wheat yield was 2 396.3 and 1 680.2 kg·hm^-2, the loss rate was as high as 97.5% and 87.9% in the plots with wheat sowing amount at 67.5 and 135.0 kg·hm^-2, on the verge of failure. 【Conclusion】The dynamics of emergence, plant height and fresh weight of D. sophia were closely related with phenology. The damages of D. sophia can be effectively controlled and the impact of D. sophia on wheat production can be reduced by timely control and rational close planting.

Key words:  Descurainia sophia, occurrence dymamic, wheat, yield components