Live Oaks in North Texas
If you live in North Texas you probably have a live oak tree. If you don’t have one than I can guarantee someone on your block has one. Live Oaks, Quercus fusiformis are a common street tree in Grapevine providing shade after a few years. They are long lived and have very few insect or disease issues. They are ever green, keeping their green leaves year-around. They produce small acorns. Some years they will be heavy with acorns and some years they can be light producers.
The question I get most about live oaks is about galls that form on them. There are galls that form because of a disease, Agrobacterium, and there are galls that form because of very tiny wasps. Most of the questions are about the galls caused by wasps. There are several different tiny wasps that lay eggs and sting the area of the leaf causing the tree to react by producing a gall to cover up the eggs. The hedgehog gall wasp triggers leaf galls with orange fuzz, usually on the undersides of the leaves. The mealy oak gall wasp causes woody twig and stem galls on live oaks so if you see the balls on twigs, it is probably from the mealy oak gall wasp. If you look closely you can usually see tiny holes in the galls where the larvae escaped from the gall ball.
Galls are generally harmless, and treatment is not really necessary. Affected foliage may drop early. Heavy populations of large galls, such as the gouty gall, may cause some die back or limb drop. Insecticides that target gall-producing insects must be applied when the insects are laying eggs. But the use of an insecticide may harm beneficial insects that offer biological control. You can prune and discard infested parts if you like.
If your live oak has big knots in a limb, that is more likely burls. They are like a benign tumor on a person. They could be unsightly, but don’t hurt anything as far as tree growth. If your live oak has a big growth at the bottom of the trunk it could be Crown galls are growths instigated by Agrobacterium tumefaciens, a soil bacteria. These are also like tumors and can grow bigger, but probably won’t kill your tree unless they are so big they strangle off the water supply.
Occasionally, I get the odd call about “Spider webs all over the trunk of my live oak”. These look really strange but are nothing to worry about. This is bark lice. They really are lice, they are small foraging insects that actually helpful. The bark lice come in and basically clean off your bark of things like mold and algae and dead tissue, then move on to another tree. So if you see spider webs covering your bark just think of it as a live oak tree bark cleaning service.
An interesting fact from “Trees of Texas”:
Live oaks were once prized for their naturally curved limbs and trunk, used by shipbuilders in the 18th Century to fashion the ribs and planking of tall sailing ships, such as “Old Ironsides.” Refitting that ship in the 1980’s included specialty pieces cut from live oaks in Texas that had been killed by the oak wilt fungus.”