Beginner

Scientific Name
           Pseudococcus maritimus

Identification

• Egg, salmon colored, elongated oval
• Eggs are laid in masses of waxy filaments that have a cottony appearance.

Nymphs

• First instar nymph, or crawler, is pink to salmon colored and has well developed legs.
• 0.06-0.12” long.
• The crawler is covered with a light coating of waxy granules, giving it the appearance of being coated with flour.
• After settling to feed, the crawler molts into a sedentary nymph, and the coating of wax becomes heavier. The sedentary nymph has poorly developed legs. It is pink to purple, but the waxy filaments give it a whitish cast.
• All stages of the female are similar, varying in size. 

Adults

• Soft, oval, flattened, distinctly segmented body.
• Adult female is 0.25 to 0.5 inch long, pink to dark purple, and with a white, mealy, wax secretion.
• Long posterior filaments along the lateral margin of the body become progressively shorter toward the head.

Damage

• Grape mealybugs can transmit grapevine leafroll-associated virus-3
• Crawlers are the most mobile and capable of transmitting the virus
• In heavy infestations, mealybug may move to fruit clusters.  As they feed, they excrete a sugary honeydew which supports the growth of sooty moulds which may cause fruit marking and rejection at the winery.
  

Often Confused With
Spider nests under bark
Powdery mildew on clusters

Period of Activity
Overwintering crawlers move from under the bark in the spring, usually peaking around bud break.  This stage is the most mobile and the best vector.  Later instars and adult females will feed under the bark of trunks and cordons.  The summer generation of crawlers peaks around cluster close.

Scouting Notes
Overwintering egg clusters can be observed by peeling back the bark from older trunks and cordons in the late winter and early spring.  Crawlers from overwintering egg clusters start to move out from under the bark as temperatures warm in the spring.  Look for them on canes and spurs and later near the base of young leaves.  As they progress through their development, they move down to areas with loose bark.  In severe infestations, sooty mould will be present on leaves and fruit clusters.

Threshold
There is no threshold for mealybugs.  If they are present, and grapevine leafroll-associated virus-3 is also present, treatment is required in order to prevent the spread of the virus.

 

Advanced

Scientific Name
           Pseudococcus maritimus

Identification

• Egg, salmon colored, elongated oval
• Eggs are laid in masses of waxy filaments that have a cottony appearance.

Nymphs

• First instar nymph, or crawler, is pink to salmon colored and has well developed legs.
• 0.06-0.12” long.
• The crawler is covered with a light coating of waxy granules, giving it the appearance of being coated with flour.
• After settling to feed, the crawler molts into a sedentary nymph, and the coating of wax becomes heavier. The sedentary nymph has poorly developed legs. It is pink to purple, but the waxy filaments give it a whitish cast.
• All stages of the female are similar, varying in size. 

Adults

• Soft, oval, flattened, distinctly segmented body.
• Adult female is 0.25 to 0.5 inch long, pink to dark purple, and with a white, mealy, wax secretion.
• Long posterior filaments along the lateral margin of the body become progressively shorter toward the head.

Damage

• Grape mealybugs can transmit grapevine leafroll-associated virus-3
• Crawlers are the most mobile and capable of transmitting the virus
• In heavy infestations, mealybug may move to fruit clusters.  As they feed, they excrete a sugary honeydew which supports the growth of sooty moulds which may cause fruit marking and rejection at the winery.
  

Often Confused With
Spider nests under bark - white covering is more filamentous while mealybug ovisacs are flaky.

Powdery mildew on clusters - both are grey but sooty mould tends to be sticky and mealybugs are generally present.

Biology
Grape mealybugs have two generations per year.  They overwinter as eggs under the loose bark on trunks and cordons. These are the preferred feeding sites, making them inconspicuous to growers. Increasing summer populations move to new tissue growth to feed. Eggs can be laid on all plant parts during the season. As populations build, migrating mealybug populations may move to clusters during July and August, causing direct crop damage with the development of sooty mould which grows on the sugar excretions of the mealybug. Most females return to old wood to lay eggs that hatch from mid-June to July. First generation crawlers then move out to the green portions of the vine to feed on fruit and foliage in late June or early July; mostly immatures are seen through July. Adult females will appear in late summer and early fall. Some females will oviposit in the fruit clusters but the majority of the females return to the old wood to lay the overwintering eggs. Ants are often found in association with mealybugs as they feed on the honeydew and tend the mealybugs, protecting them from predators and pathogens.

Period of Activity
Overwintering crawlers move from under the bark in the spring, usually peaking around bud break.  This stage is the most mobile and the best vector.  Later instars and adult females will feed under the bark of trunks and cordons.  The summer generation of crawlers peaks around cluster close.

Scouting Notes
Overwintering egg clusters can be observed by peeling back the bark from older trunks and cordons in the late winter and early spring.  Crawlers from overwintering egg clusters start to move out from under the bark as temperatures warm in the spring.  Look for them on canes and spurs and later near the base of young leaves.  As they progress through their development, they move down to areas with loose bark.  In severe infestations, sooty mould will be present on leaves and fruit clusters.

Threshold
There is no threshold for mealybugs.  If they are present, and grapevine leafroll-associated virus-3 is also present, treatment is required in order to prevent the spread of the virus.

Management Notes
Many natural enemies play a part in the biological control of mealybugs. At least five species of parasitic wasps attack grape mealybugs in California. Little research on these parasites has been conducted, but it is assumed they play a prominent role in regulating populations. The impact of the different species varies from time to time and place to place. Grape mealybugs that are parasitized by two tiny wasps, Acerophagus notativentris and Pseudophycus angelicus, have multiple emergence holes that are easily seen with a hand lens. Ants must be controlled to keep them from interfering with these natural enemies. To ensure survival of parasites, do not use disruptive insecticides during the growing season.

Cecidomyiid flies prey on mealybug eggs and small larvae. These predators plus lacewings, m Once established, parasites and predators can help keep populations down, but an infestation may slowly spread unless controlled with insecticides. Leaving areas of the vineyard untreated is an effective technique to increase predator and parasitoid populations, however, under heavy population pressure, this may not be feasible. When treating mealybugs, leave at least one out of every 10 acres untreated to provide a refuge for natural enemies, or treat with an insecticide that is not toxic to parasites minute pirate bugs, and spiders are important in keeping mealybug populations in check.

Insecticide treatments may be applied delayed dormant to manage the overwintering generation or at fruit set to manage the summer generation.