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Sucking Insects

May 9, 2001

Scout for sucking insects on nursery and landscape plants now to prevent significant injury. The main scales and mealybugs now are oystershell scale (Lepidosaphes ulmi), scurfy scale (Chionaspis furfura), Fletcher scale(I> (Parthenolecanium fletcheri), pine needle scale (Chionaspis pinifoliae), and taxus mealybug (Dysmicoccus wistariae).

Scales and mealybugs use piercing–sucking mouth-parts to feed within the vascular tissues. This results in stunted plants, leaf yellowing, and death of plant parts (branches). Soft scales (Fletcher scale) and mealybugs produce a clear, sticky fluid exudate (honeydew), an excellent growing medium for black sooty mold fungi. Also, it attracts stinging insects, including yellowjackets. Ants, which protect scales and mealybugs from natural predators and parasitic wasps (parasitoids), are attracted as well. Hard scales (oystershell, scurfy, and pine needle) don’t produce honeydew. They cover themselves with their exudate.

Managing soft and hard scales and mealybugs involves avoiding plant stress by properly implementing cultural practices, including watering, fertilizing, proper plant placement (sun vs. shade), and selection. Pest-control materials are another option in nurseries and landscapes. These include acephate (Orthene), carbaryl (Sevin), chlorpyrifos (Dursban), diazinon, dimethoate (Cygon), insecticidal soap, malathion, and summer (horticultural) oil.

These materials are normally applied as a spray to plants and kill insects by contact. They are most effec-tive after egg hatch, when vulnerable crawlers are pre-sent. However, many also kill the natural enemies, which may lead to target pest resurgence or secondary outbreaks. Scales and mealybugs are sedentary most of their lives, vulnerable to attack by natural enemies, which may sometimes provide sufficient control.

Systemic insecticides such as imidacloprid (Merit, Pointer, and Imicide) are used to manage these pests in nursery and landscape plantings. Imidacloprid kills mealybugs and soft scales but not hard scales. Hard scales feed differently than soft scales. Hard scales tend to burst and destroy plant cells on which they feed, often bypassing vascular tissues that transport food throughout the plant. The hard scales may not take up enough active ingredient to die. Scouting early, and timing insecticide applications (if necessary), minimizes problems with these pests on nursery and landscape plants.

Author: Raymond A. Cloyd


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