Our 20-foot Houston oak has white material covering the trunk and branches from a few feet up, thickening higher. Leaves remain green. What is this and how do we treat it?
This is bark lice—also called "tree cattle" or psocids (SOSS-sids). They're harmless scavengers feeding on lichens, fungi, dead bark, and organic debris, not living tree tissue. Common on oaks along the Gulf Coast from Texas to South Carolina.
Fine silken webbing with a silvery sheen covers trunks and large limbs (not twigs/leaves). Underneath, hundreds of tiny insects may cluster. Populations peak in fall, decline in winter. The webbing is protective, distinct from destructive caterpillar webs.
Do not spray insecticides. Bark lice perform valuable cleanup. If webbing is objectionable, a strong water blast dislodges them. On trees regularly sprayed for other pests, psocids rarely appear. For more information and photos, visit Auburn University's bark lice bulletin.
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