The experiment was conducted during 3 yr to measure the effect of corn cockle (Agrostemma githago L.) competition on winter wheat (Triticum aestivum L. ‘McDermid’) grain yield. In all years corn cockle was removed monthly in separate treatments from emergence (October) to harvest (July). Hand-weeded and weedy controls were compared to herbicidal control using treatments of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile). Reductions in yield of wheat as affected by competition from corn cockle were not significant if weeds were removed before February of each year in winter wheat that had been seeded the previous October. Bromoxynil controlled more weed plants when applied on corn cockle that had less than four leaves (fall treatment). Corn cockle densities of 170 to 340 plants/m2 at the Pendleton, Oregon site lowered wheat yields an average of 18% when competition was eliminated by March. Competition that continued until wheat harvest (July) reduced yields 60%.

Field studies were conducted near College Station, TX, in 2006 and 2007 to evaluate the economic impact of common sunflower interference in field corn. A density of one common sunflower per 6 m of crop row caused a yield loss of 293 kg ha−1. Estimated losses at a net corn price of $0.08 kg−1 was $92 ha−1 for infestation levels of four common sunflower plants per 6 m of row. Corn yield was increased by 32 kg ha−1 by each 1,000 plant ha−1 increase in corn planting density. Corn planting densities of 49,400 and 59,300 plants ha−1 provided the greatest net returns with or without the presence of common sunflower competition. Corn yields were reduced by extended duration of sunflower competition, with losses exceeding 1,500 kg ha−1 per week and increasing in magnitude at a decreasing rate throughout the growing season. Herbicide treatments provided net returns of $600 to $1,300 ha−1 above no weed control in both 2006 and 2007. Net returns of $609 and $653 ha−1 were obtained without the use of any herbicide for sunflower control. Determining the economic impact of common sunflower interference in field corn allows producers to estimate the overall net return on the basis of duration of common sunflower interference and density, while considering varying net corn prices, crop planting density, and herbicide application costs.