本研究主要目的為探討紫、白花藿香薊不同密度下對玉米生育及產量之影響，試驗結果顯示藿香薊對春、秋作玉米生育及產量影響，均隨藿香薊植株密度增加而使玉米地上部與根乾重皆顯著減少。對秋作玉米產量而言，當紫花藿香薊密度為每平方公尺10株時玉米種子產量減少6%，但密度增加為每平方公尺40株時則玉米產量減少達25%；而秋作白花藿香薊密度每平方公尺10株對玉米種子產量減少10%，但當增加為每平方公尺40株則使玉米產量減少達29%。對春作玉米產量而言，當紫花藿香薊密度為每平方公尺10株時玉米種子產量減少2%，但當密度增加為每平方公尺40株時則使玉米產量減少達16%；而春作白花藿香薊密度為每平方公尺10株時玉米種子產量減少7%，但當密度增加為每平方公尺40株時則使玉米產量減少達20%。

The main purpose of this study is to evaluate the influence of Ageratum spp. density on the growth and yield of corn. Results were summarized as following: Results of corn growth as affected by two Agercitum spp. in spring and fall experiments showed that the higher densities of Ageratum resulted in the reductions of shoot dry weight, root dry weight, leaf area and branch number of corn plants. In fall, 10 plants/m^2 of A. houstonianum Mill. decreased the yield of corn by 6% and 40 plants/m^2 of A. houstonianum Mill. decreased the yield of corn by 25%. Two densities of A. conyzoides L., similar to A. houstonianum Mill., resulted in 10% and 29% reductions of corn yield, respectively. However, the effect of these two Ageratum spp. on corn yield was diminished in the spring experiment.