Effect of Weed Competition on Sunflowers

Sunflowers ( Helianthus annuus L.) produced maximum seed yields when kept weed free for a period of 4 to 6 weeks after planting. This was accomplished with one cultivation anytime between 2 and 6 weeks after the early planting in 1969, with two cultivations 2 and 4 weeks or 4 and 6 weeks after the late planting in 1969, and with one cultivation at 4 weeks after either the early or late planting in 1970. The average height of sunflower plants was not influenced by weed competition if weeded at either 2 or 4 weeks after planting, whereas, head and seed size were not affected if weeded at 4 weeks after planting. The oil content of seed was higher in plots with the least amount of weed competition.