Brown soft scale, Coccus hesperidum
Brown soft scales are small flattened oval insects that are common pests of greenhouse and house plants, and is the most important scale insect that occurs on indoor grown plants in Colorado. Scales decrease plant vigor by removing phloem and excrete sticky honeydew. When full-grown it is about 4-5 mm long (1/8-in) and normally has an oval body form, although shape can vary depending on the site of the plant where it develops. The body is flat, appearing only slightly domed when viewed from the side. Color ranges from yellow-green to yellow-brown and scales may be mottled with brown spots. Older scales usually become darker brown.
- Brown soft scale is a common insect pest of indoor and greenhouse plants, including Ficus, schefflera, English ivy and citrus.
- Adult brown soft scales are yellow to brown oval and flattened, they can be found on leaves stems and petioles.
- When feeding, brown soft scales excrete a shiny, sticky fluid called honeydew that may cover leaves.
- Insecticidal soaps or horticultural oils can control brown soft scale, but these will require multiple treatments to be effective.
A pool of honeydew on a citrus leaf. The honeydew was ejected horizontally about one inch from the scale insect, which can be seen on the adjacent stem. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org.
Adult brown soft scale. Image credit: John A. Davidson, Univ. Md, College Park, Bugwood.org.
Various life stages of brown soft scale and honeydew on Ficus. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org.
Life history and habits
When mature, the female produces eggs that hatch within her body, producing very tiny (0.4 mm) first stage scales known as crawlers. Crawlers may live for a few days under the protective cover of the mother scale, but later move to colonize other areas of the plant. Stems of plants are usually favored sites where brown soft scales will settle, but they also can occur on leaves. The crawler period is the most mobile stage of the insect and is the stage that would infest new plants. Crawlers can be moved and carried while handling infested plants and may be able to be blown short distances.
Once adult females begin to reproduce, they do so continuously, so that a few crawlers will be produced daily over 3-4 weeks or more, after which the female dies. On indoor plants multiple generations will be produced each year. Because the scales are laying eggs over an extended period, generations overlap and there will be no distinct annual peaks in egg production and new crawlers.
Brown soft scales injure plants while feeding with their piercing-sucking mouthparts. These are used to reach the sugar-rich fluids present in the phloem of the plant. Sizable colonies can remove large quantities of plant fluids and can cause wilting and decrease plant vigor, but they seldom kill their host. As they feed, the scale insects excrete excess water and sugars, producing honeydew, a sticky, shiny fluid. Large amounts of sticky honeydew can cover leaves and create serious nuisance problems. In Colorado, brown soft scale is only known to occur on indoor grown plants but occurs year-round on many kinds of landscape plants in areas within the United States that have milder winters.
Early detection of this insect can greatly benefit management. The insect can be difficult to detect since they are small and blend in well with the plant itself. However, the honeydew they produce can be a great diagnostic tool. The honeydew may pool next to the insect or be ejected and land on leaves below the insect. It is also important to note that honeydew can be produced by other pests such as aphids and mealybugs.
In outdoor settings there are often numerous natural enemies that attack and greatly limit brown soft scale. Most important are several types of small parasitoid wasps that develop within the body of the scale, ultimately emerging through a hole they cut in the back of the body. Presently there are no reliably effective natural enemies available to control brown soft scale indoors. If it is practical to move indoor plants outdoors then some biological control can occur by some of the generalist natural enemies that are normal residents in yards – lady beetles, green lacewings, various predatory flies and other beneficial insects. Moving plants outdoors also allows plants to be easily sprayed and washed so that they honeydew can be removed.
There are several insecticides that can be used to control brown soft scale. Insecticidal soaps and oils can be effective means of control if applications are repeated several times and thoroughly cover insects.
Murray, M., and E. Hodgson. 2020. Utah State University – Extension. Available https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1952&context=extension_curall
University of California. 2017. Brown soft scale. University of California – Agriculture and Natural Resources. Available https://ipm.ucanr.edu/agriculture/citrus/brown-soft-scale/