Bah “Mealybug”

I have been finding white fuzzy stuff on some of my house plants and have been unable to get rid of it. What could it be and what can I do for it? This question sounds very much like someone has a mealybug infestation. Mealybugs are members of the order Homoptera, family Pseudococcidae. They have a worldwide distribution, occurring in all except the polar regions. They are one of the most economically important groups of insects known to humans because they attack many cultivated food, ornamental and household plants.

 

Mealybugs are so named because many of the known species are covered in a whitish ‘mealy’ wax, which helps retard the loss of water from their soft bodies. They are really soft scales with small (1/4"), oval, soft, segmented bodies dusted all over with white powder. They often have long radiating threads of the same secretion around the margin of their body.

 

Mealybugs go through a gradual metamorphosis; egg, nymphs and adult. The nymphs resemble the adult except that their body parts are out of proportion with each other, and they do not have fully developed wings. With each molt, the nymphs gradually develop wings and take on the body proportions of an adult. Nymphs have the same type of mouthparts as the adult, and they both eat the same kind of food. Colonies look like small tufts of cotton along veins on underside of leaves and at base of leaf stems. If environmental conditions are right mealybugs can build to huge numbers in a very short time and cause considerable damage.

 

Female mealybugs, depending on the species, will either lay eggs inside cottony egg masses or will give birth to live crawlers beneath their bodies. On hatching these juveniles, known as ‘crawlers’, move away from the cocoon and search for suitable feeding sites in sheltered areas. The juveniles progress through five molts before reaching adulthood.  In the case of the males, the last juvenile instar pupates in a silk cocoon, and emerges as a winged adult. Adult males do not feed, having no mouthparts — their sole purpose is to mate with females and pass on their genes to their many offspring. Adult females usually will live about 30 days.

 

The mouth parts of mealybugs are piercing-sucking, they insert these straw-like mouthparts, known as ‘stylets’, into plant tissue and either remove plant fluids and nutrients, or they excrete toxic salivary compounds into the plant tissue. This feeding weakens and stunts plants, causing leaf distortion, yellowing, and even total leaf loss. In some cases, plants can be killed. Plants most commonly attacked are coleus, croton, fuchsia, poinsettia and cacti.

 

Mealybugs are similar to whiteflies and aphids: they produce large amounts of waste product (honeydew) which coats plants and surrounding surfaces. This sticky layer is a perfect growth medium for a black fungus commonly known as "sooty mold". This mold damages plants by covering leaves and reducing light available for photosynthesis.

 

So what can be done to rid prize houseplants from this persistent pest? The key aspect of management is to detect the infestation before it becomes too difficult and costly to deal with. There are many things you can do to prevent an infestation from occurring. Inspect all houseplants regularly while watering to detect infestations. Check new growth and underneath leaves at least once a week for crawlers and/or egg masses. Use sticky cards to monitor for winged adult males.

 

Inspect all houseplants carefully for infestations before making a purchase. Do not bring infested plants into the house. All newly acquired plants, including gift plants, should be isolated for at least two weeks from those already in your house. This will minimize the chances of spread of unnoticed pests to nearby plants.

 

Clean pots thoroughly and inspect pots and edges of trays for egg masses and/or crawlers. Mealybugs prefer nitrogen rich succulent tissues on which to feed so over-fertilization can lead to problems. Water and fertilize at the minimum level required by the plants to control insect populations indoors. Also i

 

f possible avoid using fiber filler material between pots in planters that can harbor crawlers and egg masses and remove infested parts of plants immediately.

 

Mealybugs can be flushed off leaves with water. This can provide some immediate relief, but rubbing off colonies with a cloth is recommended so crawlers are removed and/or crushed and not merely displaced. Many types of oil sprays and soap sprays are commercially available. Insecticidal soaps and horticultural oils (when not phytotoxic) are most effective if they are applied underneath leaves, on pots, as well as areas surrounding plants where crawlers could migrate. Oil sprays suffocate the insects while soap sprays cause the insect’s cell membranes to rupture, effectively causing it to desiccate. If you chose to use a pesticide, remember, always read the entire label and only use the product when it is absolutely necessary. Pesticides can provide short-term control, but mealybugs persist in hard-to-reach places so they are not recommended as a long-term solution. Heavily infested plants should be discarded.

 

Call the UNH Cooperative Extension's Family, Home & Garden Education Center 's Info-Line toll-free at 1-877-3984769 for "Practical Solutions to Everyday Questions." Trained volunteers are available to answer your questions Monday through Friday from 9 am to 2 pm .

 

By Rachel Maccini, Coordinator Family, Home & Garden Education Center, UNH Cooperative Extension, Hillsborough County