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Plant Protection - Mealybug Management (Tech Tip )
By Marla Faver, Syngenta Technical Services

A mealybug outbreak can be very frustrating for growers because managing these pests is very difficult. Mealybugs are nearly impervious to most insecticides because they have a protective wax covering. Adult females, egg sacks (ovisacs) and some species of older nymphs have this waxy covering. Female mealybugs are soft, oval insects without wings; male mealybugs are gnat-like insects with two wings and long tails of white wax. Very young nymphs are flat, oval, yellowish in color and generally do not have a waxy coating.

Mealybugs are homopterous insects like aphids and whiteflies. They have piercing/sucking mouthparts called stylets, which they use to pierce the plant and feed on plant fluids from the mesophyll or stems. Some species inject a toxin as they feed causing additional damage to the plant.

Madeira Mealybug on Plant Stem

Below are some common mealybugs found on ornamentals.

  • Citrus mealybug (Planococcus citri): Found underneath the white, waxy coating. Body color is orange to purple with a dark line down the middle of the back.
  • Longtailed mealybug (Pseudococcus longispinus): Has anal filaments that are usually at least as long as the body.
  • Madeira (Phenacoccus madeirensis): Found underneath the white, waxy coating. Body color is purple with two stripes down the back separating three rows of white tufts.
  • Pink hibiscus mealybug (Maconellicoccus hirsutus): Small (about 3 mm long) and pink in body.
  • Various root mealybugs.

Injury from mealybugs includes yellowing leaves, distorted growth, premature leaf drop and heavy populations, which may result in plant death. Mealybugs produce sweet, sticky liquid called honeydew, which supports the growth of an unsightly black fungus (sooty mold) that grows on the plants.

Mealybug control and insecticide management

  • Inspect host plants for waxy white deposits and the presence of ants and/or sooty mold. Mealybugs have a cryptic behavior and tend to aggregate or establish themselves in buds, base of stems, petioles and undersides of foliage.
  • The hydrophobic (water-repelling), waxy body repels hydrophilic (water-loving) insecticides, making control with contact insecticides difficult.
  • Be prepared to repeat contact insecticide applications two or more times to kill nymphs that hatch from protected eggs and adults or nymphs that are protected by plant tissue. Since populations overlap, the need to apply insecticides frequently increases the development of insecticide resistance.
  • Systemic insecticides, such as Flagship® 25WG insecticide, applied as a drench or granular, offer the most reliable control because the active ingredient is available as the mealybug feeds rather than working by contact. It is important to avoid overwatering plants after application so roots can absorb the active ingredient.
  • Systemic insecticides like Flagship are generally compatible with beneficial insects.

Control of Miscanthus Mealybug (Miscanthiococcus miscanthi) on Miscanthus with soil applied treatments of Flagship

(Frank, NCS, 2011)

After a soil application of Flagship insecticide, the number of adult mealybugs per stem was evaluated at 26 and 56 days after treatment. Plants treated with Flagship had significantly lower mealybug populations than those plants left untreated.

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