PhotoAsk your average gardener why the despised weed crabgrass is successful and he'll say it's because it grows fast and crowds out neighboring plants.

But the truth is even worse:  A new study in the Journal of Agricultural and Food Chemistry has found that crabgrass actually produces its own herbicides that kill nearby plants.

The weed is not only a headache for lawns and home gardens, but also a major cause of crop loss on farms, so there has long been interest in learning more about how it manages to be so aggressive.

Scientists have long suspected that the weed thrived by allelopathy,  which occurs when one plant restricts the growth of another by releasing toxins.

Chui-Hua Kong and colleagues set out to determine if crabgrass in fact has the ability to poison its neighbors. Kong’s team isolated three chemicals from crabgrass that affect the microbial communities in nearby soil and did indeed inhibit the growth of staple crops wheat, corn and soybeans.

“The chemical-specific changes in [the] soil microbial community generated a negative feedback on crop growth,” the scientists said, noting that the chemicals also would have a direct toxic effect on other plants.  

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