Why farmers may want to keep, not kill, weeds

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Farmers looking to reduce reliance on pesticides, herbicides, and other pest management tools may want to heed the advice of agricultural scientists: Let nature be nature—to a degree.

“The benefits of weeds have been neglected. They’re often seen as undesirable, unwanted. We’re now beginning to quantify their benefits.”

“Managing crop pests without fully understanding the impacts of tactics—related to resistance and nontarget plants or insects—costs producers money,” says Antonio DiTommaso, professor of soil and crop science at Cornell University and lead author of a new study in the journal Weed Science.

“We are taking a renewed look at a holistic, sustainable integrated pest management (IPM) approach,” DiTommaso says.

In corn production, for example, maintaining a few villainous milkweed plants in the middle of a cornfield may help minimize crop loss from the destructive European corn borer. The milkweed plants can harbor aphids (destructive sap-sucking flies) that produce a nectar food source for beneficial parasitic wasps Trichogramma.

The wasps, in turn, lay eggs inside the eggs of the European corn borer, killing the corn borer eggs—reducing damage to the crop.

“Production management rarely considers the benefits of weeds in agricultural ecosystems,” says DiTommaso. “Let’s look at the big picture. If we open our eyes—even if it’s a weed growing in the cornfield—we show it could be beneficial. Integrating weed benefits will become increasingly important, as pest management is likely to move from total reliance on herbicides and transgenic crop traits for control, because of increasing resistance of weeds to these products.”

More weeds, more butterflies

One additional side benefit for having a few milkweed plants in a field of corn is that it serves as a breeding place and food source for monarch butterflies. As of late, monarch numbers are down, and the US Fish and Wildlife Service is evaluating a petition to have them protected under the Endangered Species Act.

While some growers elect not to use engineered crops, producers may see a return to IPM methods from two decades ago, as resistance could easily occur when relying on a single tactic.

Wasps might be the perfect weapon to kill aphids

With increasing no-till production, producers will inevitably see rebounds in perennial weeds—such as milkweed, the researchers say. Thus, some growers may be willing to tolerate a low milkweed population in favor of providing livable plant space for monarchs.

“Every organism in an agricultural system plays multiple roles,” says John Losey, professor of entomology. “If management decisions are based solely on the negative aspects, yield and profit can be lost in the short term and broader problems can arise in the longer term.”

Integration of the weed costs and advantages will become important.

“The benefits of weeds have been neglected. They’re often seen as undesirable, unwanted. We’re now beginning to quantify their benefits,” says Kristine M. Averill, a research associate.

“It’s very important to recognize the benefits of all the species within the crop field—that includes both the crops and the weeds—not to mention cover crops. Weeds can offer ecosystem services, such as soil erosion protection and pollination services for the benefit of insects,” Averill says. “They can be part of a restorative cycle.”

Source: Cornell University