Whether growing ferns indoors, in a greenhouse or outside, pests can infest the plants and ravage the fronds. Some insects even kill ferns if left untreated. The most common pests that appear as white insects on ferns include mealybugs, fern scales, thrips and whiteflies. Identifying the exact insect on your ferns is crucial to properly controlling the infestation.
Mealybugs infest ferns, appearing as tiny white dots on the leaf axils and undersides of the fronds, according to the University of Florida. Mealybugs appear cottony and can also infest the root area. You might see a sticky, clear liquid called honeydew on the fern fronds. It is a substance that mealybugs excrete. The honeydew is often a host for a secondary disease like black sooty mold. The plant may look stunted or is dying. To treat a mealybug infestation, use a systemic insecticide on your ferns or a soil-drench insecticide if the mealybugs are around the root area.
The male fern scale insects are white, tiny, double-winged and gnat-like, according to the University of Minnesota. The males are only 1 mm long and have white armor with three ridges. The females are light-brown, oyster shell-shaped and 1-½ to 2-½ mm in length. If fern scales infest your ferns, you'll notice that the plants are disfigured or have yellow spots on the fronds. Control fern scales with horticultural oils applied to the foliage in two separate treatments about two weeks apart.
Depending on the species, thrips come in a variety of colors. Some appear white or yellowish. Thrips are tiny insects with double pairs of wings that have long fringes of hair around the wing edges, reports the University of Florida. Using a magnifying glass, you can also see the thrips' chewing mouthparts. Thrips are most attracted to plants with dark foliage, such as ferns, causing the fronds to curl and distort. You may also see slivery-gray scars on the fern fronds from where the thrips were feeding. Control thrips with pesticides labeled for the specific insect.
Adult whiteflies sometimes bear bands or markings of different colors on their wings, and the nymphs and adults may have white waxy deposits on their bodies, according to the University of California. You'll find whiteflies clustered in groups on the undersides of the fern fronds, sucking the plant sap. Whiteflies excrete honeydew. If whiteflies infest your ferns, the fronds turn yellow and die. The honeydew can also cause a black sooty mold infection. Whitefly infestations are difficult to control using insecticides. Introduce natural predatory insects that kill the whiteflies to control the population. Lady beetles, minute pirate bugs, bigeyed bugs and lacewings all feed on whiteflies.