A fungicide is a chemical substance designed to kill fungi or prevent them from growing. Fungi are living organisms that include mushrooms, molds, and yeasts. While some fungi are helpful (like the yeast that makes bread rise), others cause serious problems by damaging crops, rotting wood, or making people sick.

Farmers spray fungicides on their fields to protect plants from fungal diseases that could destroy entire harvests. Without fungicides, a wheat field infected with a fungus called rust might produce almost no grain at all. Gardeners use fungicides to stop black spot from covering rose leaves or to prevent tomato plants from developing blight.

Around your house, you might find fungicide in bathroom sprays that prevent mildew from growing on shower tiles, or in treatments that protect wooden decks from rot.

Scientists work to develop fungicides that target harmful fungi while leaving beneficial organisms unharmed, since fungi play important roles in nature, like breaking down dead plants and helping tree roots absorb nutrients from the soil.