A Moment of Science

Why Crabgrass Always Wins at Monopoly

Crabgrass, the killer weed, inflicts chemical warfare on lawns and farms.

Suburban house and lawn are foregrounded by a patch of dandelions.

Photo: Stacy Brunner (Flickr)

Killer crabgrass will make a constant gardener out of you.

Crabgrass is an ugly, obnoxious weed that is the scourge of the perfect lawn and its perfectionist gardener. Along with being an eyesore, it’s also responsible for a substantial amount of crop loss on commercial farms.

Weeding Out Competition

Common wisdom says that crabgrass is hard to get rid of because it crowds out the plants around it, and does not allow them to get enough space and nutrients. However, scientists have long wondered if crabgrass dominates your lawn’s real estate by using a technique called allelopathy. This literally means “others suffering,” and occurs when a plant harms another by emitting toxic substances into the environment, usually through the soil.

Researchers from Nankai University, China Agricultural University, and the Chinese Academy of Sciences all found that crabgrass uses this method of “weeding out” neighboring plants.

In their experiment, researchers isolated three chemicals from crabgrass roots and nearby soil, and then added them to potted plants of wheat, maize, and soybeans. Sure enough, the plants treated with crabgrass toxins did not grow as well.

Chemical Warfare

Tests revealed that the compounds reduced the amount of carbon in the soil’s microbial biomass. This means crabgrass can actually change the makeup of the bacteria in the dirt around it. Since plants rely on bacteria in order to absorb key nutrients such as nitrogen and organic compounds, the vicious weed makes life extremely hard on its surrounding neighbors.

So the next time you squirt Round‑Up on that pesky patch of crabgrass, remember that the weed is emitting a little herbicide of its own. It’s chemical warfare, right under your nose.

  • Meech

    Why are dandelions pictured with this article?

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