Mealybugs

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General Description

There are two identified species of mealybugs that attack tree fruits in the Southern Interior - the apple mealybug and the grape mealybug. Grape mealybug has been present for many years on grapes, but has been found on apple. It is a major pest of pears in Washington State.

Hosts

Apple mealybug - Apple, sweet cherry, peach

Grape mealybug - All tree fruits, grapes, and related ornamental trees and shrubs.

Damage

Apple mealybug is the vector (transmits) of the virus that causes little cherry disease in sweet cherry. Read the description of Little Cherry Disease for information on symptoms of infection.  High populations of both species can produce honeydew which drips onto host fruit and causes russet and growth of black sooty mold. 

Identification

Life stages of both species of mealybugs are very similar in appearance.

Egg - Salmon-coloured, oval, laid in white cottony masses.

Nymph (crawler) - Newly hatched nymphs are yellow to brown and mobile; secondary nymphs are less active, slightly darker in colour with a fine coating of white waxy filaments. 

Adult - Female is wingless but mobile, with an oval flattened body up to 5 mm long fringed with short waxy filaments (Fig. 1).

Figure 1. Mature mealybugs. (BCMA)

Female grape mealybug has four long waxy filaments extending the end of the  body (Fig. 2) which are missing on the female apple mealybug; both appear as small white powdery patches in bark crevices, pruning scars, and in crotches of branches. Adult males are winged and very small.

Figure 2. Grape mealybug. (Larry Strand, University of California Statewide IPM Program)

Life History

The apple mealybug overwinters as nymphs which merge to feed on host leaves before maturing in mid-summer. These adults produce the overwintering nymphs. It has only one generation per year. The grape mealybug also overwinters as nymphs that emerge the followimg spring to feed on host leaves before changing into adults about mid-summer. A second generation of adults apears in late fall which produces the overwintering nymphs.

Monitoring

To detect crawlers in the spring (both species) and grape mealy bug nymphs in late summer, wrap two-sided sticky tape around a smooth part of twigs where adults or  damage was noted last season. Replace the tape every 3-4 days and examine for the small yellow to brownish crawlers using a hand lens or magnifying glass. Use this technique to properly time sprays against crawlers which are the most susceptible stage for chemical control.

To detect mealybug infestations during the summer, visually examine the trees for presence of honeydew and/or sooty mold on leaves and branches, and for adults hiding in bark crevices, crotches and other protected sites on the trees. Mark infested trees for spot treatment and for monitoring crawlers.

Management

Biological Control

In the absence of harmful chemicals, biological control agents can usually keep mealybug populations below damaging levels, Ladybird beetles, lacewings and predaceous bugs feed on adults, a predaceous midge attacks eggs, and several diseases infect the mobile stages. 

Cultural Control

Older standard trees are most susceptible to infestations because they provide more hiding places for all stages and less exposure to sprays if not properly pruned to open up the canopies. Mealybugs prefer to feed on tender new growth, so sucker removal before the end of June will aid in reducing the risk of damaging population levels.

Chemical Control

The following sprays are recommended to control the apple mealybug in cherry orchards where little cherry disease has been found, or in areas where little cherry disease is known to occur. Recommended control products and timings include:

1. Dormant: Apply an oil to control over-wintering nymphs. Use high volume application techniques as recommended for San Jose scale control.

2. Petal-Fall: Admire used at this stage are effective against mealybugs. High volume airblast or hand gun applications are the most effective.

3. Summer: The major period of mealybug movement from tree to tree is during the summer when nymphs are on leaves and can be dispersed by wind. Nymphs are also the easiest to kill with chemicals.  Apply Movento 240SC after petal fall to control crawlers. Movento is toxic to bees. Make sure honey bees are no longer foraging.  Low volume air blast sprays of Admire, Cygon, or Lagon applied for control of cherry fruit fly are also effective for the control of apple mealybug nymphs.  The closer to harvest these materials are applied, taking the minimum days before harvest into account, the more effective is the mealybug control.

4. Post-harvest: A post harvest spray of Admire, Cygon or Lagon applied against cherry fruit fly will also aid in reducing the number of overwintering crawlers.

Apply Movento after petal fall is effective against mealybug crawlers in other stone fruits. 

In apple and pear orchards, pre-bloom applications of diazinon against aphids and leafrollers will also control any crawlers present. Apply Movento after petal fall to control crawlers. Make sure honey bees are no longer foraging.