Brown soft scale (Coccus hesperidum)
Cottony scale (Pulvinaria spp.)
Greedy scale (Hemiberlesia rapax)
Lecanium scale (Lecanium spp.)
Oystershell (mussel) scale (Lepidosaphes ulmi)
Pest description and crop damage Scale are sucking insects that infest vines and leaves of cranberry plants causing stunted, delayed vine growth and/or dead patches in beds. Scale presence can cause reduced fruit set on infested uprights. Small areas of infestation can be found in any part of the cranberry bed. Scale insects are often difficult to detect because they are small and relatively immobile. These insects are divided into two categories: armored scale and soft scale. Soft scale insects excrete a sugary substance called "honeydew," which becomes the substrate upon which sooty mold grows. Sooty mold accumulates on vines and is a good visual indicator of soft scale presence. Several species of scale insects are found in Pacific Northwest cranberry beds:
Greedy scale are light gray in color, circular in shape and convex. As armored scale, greedy scale have a plate-like cover (the "armor") that can be peeled off. Underneath the armor is the actual scale insect. Greedy scale measure approximately 1/16 inch (1 to 1.5 mm) when fully grown. In Oregon, greedy scale have been observed covering the woody portion of cranberry vines and can be dense enough to create dead spots in a bed. As armored scale, greedy scale do not produce honeydew. Treatment timing must coincide with initial crawler (newly hatched eggs) release to be effective. Monitoring efforts have indicated that greedy scale crawlers begin to emerge shortly before bloom, but year-to-year variation occurs.
Brown soft scale are brown in color, and flattened and oblong in shape. As soft scale, they do not have a removable "armor;" instead, their cover is fused with the insect body so that it peels away in one piece. Brown soft scale overwinter on uprights and leaves of cranberry plants and are typically located either on the upper leaf surface near the mid-rib, or on the stem. They produce multiple generations each year. They produce large amounts of honeydew; as such, black patches of sooty mold in a bed are a good indication that brown soft scale are present. Late-dormant treatment with 2% solution of insectidal soap has shown to be effective against brown soft scale. Multiple treatments will likely be necessary. Boom spray only.
Lecanium scale are hemispherical and chestnut-brown, 1/8 to 5/16 inch (3 to 8 mm) in diameter. Like brown soft scale, lecanium scale produce honeydew. Lecanium scale are a pest in only some areas of Oregon. They have one generation per year, with the crawlers emerging in June.
Cottony scale are soft scale that lay their eggs in cottony masses, often on stems of uprights and undersides of leaves. They have one generation per year. Parasitoid wasps were present in samples from a bed in southern Oregon, indicating that some biological control is in effect. This species doesn't appear to be of high concern at the moment, but is present on some beds.
Oystershell scale have been present in Oregon for decades, but numbers have been increasing in recent years. These are shaped like mussels and coat the vines, resulting in dead spots in the bed. They have one generation per year. Eggs overwinter and hatch the following season, usually around bloom. Growers report some success with pyriproxyfen applied during the crawler stage. Products such as diazinon or danitol may be effective at that time as well; further research is needed to determine efficacy.
The population of scale insect is dynamic, reflecting control by natural predators, such as parasitic wasps. The use of broad-spectrum insecticides, however, can disrupt these populations, resulting in an increasing problem with scale.
Management-chemical control: COMMERCIAL USE
Lecanium scale are usually controlled with fireworm insecticide applications that can coincide with migration of young crawlers on vines. Greedy scale and oystershell scale seem to be the most difficult to control; these may be controlled with applications for other scale insects. Brown soft scale are seldom controlled with only one or two sprays. Continue to monitor closely in subsequent seasons. In all species, the crawler stage is the most susceptible to chemical control efforts. Greedy scale crawler emergence generally occurs just prior to bloom (late April, early May) and continues through July. Work with Extension personnel to identify specific timing. To date, the most effective control for greedy scale is diazinon, although research is being conducted on the efficacy of spirotetramat, pyriproxyfen, and a product that is a spirotetramat/pyriproxyfen combination. Control efforts early in the season before generations begin to overlap will be most effective.
- azadirachtin (Aza-Direct, Neemix and other brands)-Consult label for rate. PHI 0 days. Some formulations are OMRI-listed for organic use.
- diazinon (several brands) at 2 lb ai/A. PHI 7 days. Do not apply to bloom; material is hazardous to bees. Restricted use pesticide.
- fenpropathrin (Danitol) at 0.3 to 0.4 lb ai/A. PHI 3 days. Do not apply during bloom. Restricted use pesticide.
- insecticidal soap (M-Pede and other brands)-Consult label for rate and use directions. PHI 0 days. Some formulations are OMRI-listed for organic use. Effective against brown soft scale either alone or in combination with an approved organophosphate, applied during dormant/delayed dormant season. Not effective against greedy scale. Use high label rate of soaps when used alone; use lower rate if used with an organophosphate. Spot-treat infestations in dormant/delayed dormant period at 1 to 2% v/v solution.
- horticulture oil (several brands)-Consult label for rate and use directions. Apply oil during delay-dormant stage. Time application to coincide with temperatures of 60°F, dry weather, and crawler emergence. A second application will likely be necessary 2 to 4 weeks later. Monitor vines for crawler emergence and apply oil accordingly.
- pyriproxifen (Esteem 35 WP, Knack) at 0.11 lb ai/A. PHI 7 days. Apply at dormant, delayed dormant, or in-season. Do not exceed 2 applications per year. Time in-season applications to crawler release for best results. As an insect growth regulator, evidence of this product working will be slower than typical contact insecticides.