Barklice on a tree

Homeowners across the county have reported occurrences of clumps of insects appearing on trunks of trees in landscapes. The clumps are actually composed of insects known as bark lice which move together as a family unit somewhat like a herd of cattle in a pasture. Bark lice are beneficial insects and do not pose any harm to humans, pets or to trees.

WILLIAM M. JOHNSON/Courtesy

Q: Clumps of some type of organism have suddenly appeared on the trunks of my crape myrtle and oak trees. The clumps look like bark except they move one area on the tree trunk to another area throughout the day. What might they be?

A: I have received distress phone calls and e-mails from many, many homeowners describing the same problem. Though the clumps may appear to be problematic, they are not. The clumps are composed of insects known as bark lice.

Most folks will raise an eyebrow when they think of a lice infestation. However, bark lice are not the same as parasitic lice found on humans and animals. The scientific name of bark lice occurring in our area is Cerastipsocus venosus. Another closely related species of bark lice also occurs in our growing area around mid- to late-summer; this species forms silk webbing on tree trunks.

Bark lice move together as a family unit somewhat like a herd of cattle in a pasture. Not surprisingly, they are also known as tree cattle. Bark lice do not pose any harm to humans, pets or to trees.

Bark lice are beneficial insects that feed upon lichens, fungi, algae, dead plant tissue, pollen and other debris located on tree trunks.

The adult stage of bark lice is approximately 1/4 inch long and jet black in color with a few white stripes. Each adult has a pair of very long antennae. The immature or teenage stages are known as nymphs which are wingless and have distinctive yellow and black color bands. The adults and nymphs feed in a group.

The wingless nymphs and winged adults form quarter-sized to hand-sized clusters and move about in “herds” over the tree trunk as they “graze.” Some residents have noted that the clusters will temporarily scatter when suddenly disturbed, only to rejoin again as a “herd.”

Although this species of bark lice occurs on many different species of trees, it is most often noticed on crape myrtles, probably because they are so conspicuous on that smooth, light-colored bark. I have also seen this species of bark lice on oaks. Several fruit trees (including citrus and mayhaw) in the master gardeners’ Discovery Garden in Carbide Park also have bark lice this spring.

Q: The bark on my crepe myrtles is peeling off and it looks like it has been shredded and just hangs off the trunk and some of the lower branches. Is this normal?

A: As crape myrtles age, the bark will begin to peel off. The horticultural term for this is exfoliating. This is normal and there is no cause for alarm. After the gray bark peels away, you may notice a different shade of underbark. Some of the newer varieties have colors that are cinnamon to dark brown in color. This colorful underbark adds to the beauty of a crape myrtle especially in the winter. Go ahead and peel any loose bark off once it starts shedding to hasten the exposure of the underbark.

Q: Why are there a lot of small holes in the leaves of my eggplant plants?

A: This damage is caused by insects known as flea beetles. Row covers will provide some protection. An insecticide containing carbaryl (such as Sevin) as an active ingredient can be used. Be sure to read and follow the manufacturer’s directions.

Q: When should I harvest my Irish potatoes?

A: New potatoes can be harvested as soon as they reach a suitable size. Fully-developed potatoes for storage can be harvested when the top growth turns yellow. Do not harvest potatoes when the soil is very wet. This will increase the chance of rotting.

Q: I have noticed that a lot of professional landscapers mulch trees with shredded pine bark mulch in a cone formation around the base of trees. Is this a good idea?

A: Mulching around trees is recommended. Mulching materials that come into contact with the tree trunk can severely weaken or even kill the tree. The constant moist conditions created by the mulch will rot the bark layer and damage the cambium (growth) layer of the tree. It is recommended that mulch about four inches deep be spread around the tree but kept a few inches away from the tree trunk. The rule of thumb is to build donuts, not pyramids, around trees.

Q: Will pine needles used as a mulch help lower the soil pH?

A: It is true that pine needles help create an acidic soil in native forests after hundreds or even thousands of years of growth and decomposition. But in a home landscape there is not enough time or plant litter to substantially modify our slightly alkaline gumbo clay soils.

William M. Johnson

is a horticulturist with the Galveston County Office of Texas A&M AgriLife Extension Service. Visit his Web site at http://aggie-horticulture.tamu.edu/galveston/index.html

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