Ornamental plants are subject to a number of destructive insect pests. Whether you grow a philodendron as a houseplant or use an ornamental such as the flowering hydrangea outdoors, all ornamentals can be subject to attack. Keep an eye on your plant and begin treatment early.
Over 400 species of the scale insect exist in the United States, according to the University of Florida. Two types of scale occur all around the world: armored scales and soft-bodied scales. Most scale insects measure between 1/16 to 1/8 inch and come in literally all colors of the rainbow. Their shapes can also vary, from circular to oval, thread-like or oblong to pear-shaped. These are sucking insects that feed on plants' juices: when a plant is badly infested, it becomes unhealthy and stops producing new growth, resulting in death if the insect is not controlled. The first step in controlling scale insects is to control ants, which carry the scale to a plant so they can eat their sweet excretion. If an invasion of scale occurs, spray your plant with 1 qt. of insecticidal soap spray mixed with 1 tbsp. of canola oil. Continue spraying with this mixture until all signs of the insect are gone.
Rose bushes and other ornamentals are often the feeding ground for one or more of the hundreds of aphid species. The aphid is a sucking insect that often causes plant leaves to curl and later become yellow and drop. They are small, from 1/16 to 1/8 inch long and range in color from orange to black. Some aphids help to transmit plant diseases. This insect often lives and feeds on the underside of leaves and on stems of plants. Ants help to spread aphids because they feed on their excretion, so if you control ants on your plants, you can help to prevent an aphid invasion as well as the possible spread of disease. Because aphids have soft bodies, you can control them with a spray of insecticidal soap. Spray every other day until all signs of this pest are gone.
Related to the scale insect, the mealybug affects a large number of plant species, mainly in warm, humid climates, according to Ohio State University. The mealybug is a small, soft-bodied insect that that is typically white and fuzzy. They can literally cover a plant stem. Their excretion, called honeydew, can cause a plant to develop a fungal disease called sooty mold. Affected plants will develop yellowing leaves and stunted growth. They excrete a sticky substance that ants eat, so to help control the mealybug, control ants. Spray your affected plant with insecticidal soap as soon as you notice any mealybugs. A predatory ladybug called the mealybug destroyer can also be helpful in combating this pest, according to Ohio State University.
Spider mites are common insect pests that attack both houseplants and those grown outdoors. This tiny arachnid is red, brown, yellow or green and is related to spiders. You can see its presence on a plant because of the web that it weaves: the web is more noticeable than the insect. Spider mites cause plant leaves to become flecked or discolored and sometimes they look as if they have been burned. Leaves often drop and death can result. Other insects eat the spider mite, but these predators are often killed when pesticides are used in the vicinity of the affected plant. One species of ladybug, the spider mite destroyer, is useful in controlling this pest. Other natural enemies include the minute pirate bugs, big-eyed bugs and predatory thrips, according to Colorado State University. Chemical miticides can be helpful in controlling this insect, but these products do not kill the insects' eggs, so you must repeat your application frequently. Horticultural oils and insecticidal soap can also offer some relief.