Goldenrod (Solidago altissima . L) is an Asteraceae perennial weed - a typical foreign weed in Korea that is widely propagating mostly in the southern regions of the Republic of Korea. Since Trifolium repens and Festuca arundinacea are considered major forage crops, the dominance of S. altissima may exert an adverse effect on pasture land. Considering these issues, in the present study we investigated the possible threat of S. altissima incidence through observing the growth response of T. repens and F. arundinacea with application of S. altissima crude extract. The root powder and root methanol extract were used in germination experiments by mixing the ratio of root powder and soil, in vitro seed bioassay, and foliage treatment. Our result showed that root powder and methanol extract can inhibit the growth of forage crops. In the case of methanol extract, it can reduce germination of F. arundinacea seed effectively and foliage treatment reduced shoot length, fresh weight, dry weight, and chlorophyll content of T. repens . The current results show S. altissima can inhibit forage crops growth and development. These findings could help to predict the S. altissima management and forage crop protection in Korean agricultural land.