In the stem of the Arabidopsis plant, the light-sensitive receptor CRY2 (yellow) spurs the plant to begin a growth cycle and avoid shade. Scientists at the Salk Institute in the United States have discovered a way by which plants assess the quality of shade to outgrow menacing neighbours, a finding that could improve the productivity of crops. The paper, published in the journal Cell last month, shows how the depletion of blue light detected by molecular sensors in plants triggers accelerated growth to overcome a competing plant. Despite seeming passive, plants wage wars with one another to outgrow rivals and absorb sunlight. If a plant is shaded by another, it becomes cut off from the essential sunlight it needs to survive. To escape this deadly shade, plants have light sensors that can set off an internal alarm when threatened by the shade of other plants. Their sensors can detect depletion of red and blue light (wavelengths absorbed by vegetation) and distinguish between an aggressive nearby plant and a passing cloud.