Question: I am having a problem with my Meyer lemon trees. I bought the tree last spring and didn’t seem to have any problems all summer long. Shortly after moving the trees in for the winter, I began to notice some soft, white creatures prowling the leaves and stems of the tree. What is this and what can I do about it?
Answer: Growing any kind of citrus in North Central Alabama can prove challenging yet very gratifying once you begin to reap the rewards of your labor. While the plants are relatively easy to manage and maintain with a splash of water, a little fertilizer and protection from the cold, they can be prone to some disease and insect problems when brought indoors or grown in a greenhouse. From your description, this seems to be one of the common problems that affect citrus trees, a scale insect known as cottony cushion scale.
Cottony cushion scale, Icerya purchasi, can infest a number of woody ornamentals and certain crops but common hosts include citrus, cleyera and Japanese pittosporum . Scale insects decrease the vitality of their host plant by sucking phloem sap from the leaves, twigs, branches, and trunk. Feeding can result in defoliation and dieback of twigs and small branches when infestations are extremely heavy. Heavy populations can severely reduce the yield of citrus trees. The body of the cottony cushion scale is orange-ish in color but the identifying characteristic is the large, white and cottony egg sack that is attached to the body. Each scale can carry up to 800 eggs, making the egg sack much larger than the body of the insect. The eggs hatch within a few days during the summer but can take several weeks in the winter (perhaps why they weren't initially noticed). These new “baby” scale are called crawlers and they tend to settle on soft vulnerable tissue, usually along the leaf veins on the underside of leaves. As the scale increase in size, they molt and appear red or orange for some time before they begin to produce more cottony secretions.
Aside from the obvious white egg sacks that this scale is named for, other indications of a scale infestation include large population of ants and a black mold known as sooty mold that grows on the excretions of the scales (known as honeydew). Once seen, it is only a matter of days before the population increases in size, remember that ONE egg sack can contain 800 eggs!
Though not impossible to control, cottony cushion scale can prove to be a challenging problem, especially on indoor plants. When the pest is on plants outside, their numbers are often controlled by several beneficial insects (tiny wasps and mites). When not inhibited by ants, which protect the scale as a source of food, these beneficial insects may keep the pests at a tolerable level. However, once the plant is inside, these beneficial insects cannot gain access to the scale, so the next best option is to remove the scale by hand whenever you see them. The adult scales seem to gather on major stems though they can move around. When the plants are outside, horticultural oil or insecticidal soaps are effective on the crawler stage of the scale, so timing can be important. After hand-picking the scale, wipe as much of the plant as possible (stems and leaves) with a paper towel soaked in rubbing alchohol.
Growing citrus in Alabama can be challenging and fun. With a little bit of work and patience, you will be drinking fresh lemonade in no time!
written by Hunter McBrayer of the Alabama Cooperative Extension System, C. Beaty Hanna Horticulture & Environmental Center, which is based at the Birmingham Botanical Gardens. (photo credit: Lesley Ingram, Bugwood.org)
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