If your plants leaves are yellowing and you see dark, dirty patches, you may have a mealybug problem. There are several species of mealybug that may cause you and your garden problems.

Their favorite plants include tree fruits such as citrus, apples, and peaches, grapes, potatoes, and a number of tropical plants, including houseplants. These tiny insects appear in clusters on the undersides of leaves and clumped on in the forks of twigs and branches where they suck plant juices.

As they feed, some species inject toxins that damage plant tissues. They're oval in shape, with a grainy, dusty surface that is actually a protective waxy coating. Large clumps of mealybugs may resemble fur or lint. Mealybugs will invade your garden year-round if you're in a warm climate.

In colder climates, there may be two or three generations a year. To control mealybugs, spray affected plants with insecticidal soap or a stiff stream of cold water.