The spider's silk seemed to deter the pests, even though no spiders were present.
Even when beetles were trapped in enclosures with the plants, they caused about half as much damage as normal. A similar but less pronounced effect was seen with silk from silkworm cocoons.
The gardener's tip appears in the Royal Society journal Biology Letters.
Researchers focused on two serious green bean pests -- the Japanese beetle and Mexican bean beetle. Adults of both species are hunted and eaten by web spiders.
Studies were conducted under controlled conditions both in the laboratory and outside.
In the field experiments, each treated leaf received five strands of spider silk evenly spaced along its length.
The scientists, led by Dr Ann Rypstra, from Miami University in the US, wrote: "These results provide robust support for the hypothesis that the presence of silk reduces the foraging activity of pest insects leading to lower levels of herbivory."
The freshly drawn spider silk sent out chemical signals that deterred the beetles, the researchers believe.