What's this sawdust/pollen/dirt under this tree? Disease or Normal?

Asked September 4, 2013, 8:24 AM EDT

This tree in my backyard that I cannot identify (though it may be an olive tree) keeps dropping fine sawdust or dirt or pollen to the extent that it is piling up in drifts.

I see no unusual insects on it, though at the tops of the branches there are a large number of tiny shoots.

This is north Texas, urban DFW. We have loads of insects around, mostly wasps, cicadas, crickets, spiders, ants, etc. No boring insects that I can identify, but I'm no entomologist.

Here is a gallery of pictures: http://imgur.com/a/i4kpl

Thanks!

Edit: I had some unexpected time off today so I cut down a limb and sort of cut off the top. As you can see from the last picture in my gallery it is pretty clear that something is boring in, and that it is making big tunnels. I still can't find the culprit though, and I wouldn't mind finding a way to stop it.

Thanks for your help!

Dallas County Texas trees and shrubs horticulture

1 Response

Many insects feed and make their homes in the bark, trunks and branches of shade trees and shrubs in Texas. Insect borers belong to several different insect groups including a variety of beetles, moths and horntail wasps. Most insect borers are attracted to weakened, damaged, dying or dead plants. These are referred to as “secondary invaders” because they attack only after a plant has been weakened by another stress. Secondary invaders are a symptom of other problems with the health of the tree or shrub, but may contribute to its decline. Secondary invaders include species from groups already mentioned, but also may include termites, carpenter bees and carpenter ants. Many other insects live in dying or dead trees, including natural enemies (predators and parasites) of the insect borers, sap or fungi feeders, or species which merely use the spaces provided by the tunnels and galleries as living quarters. Wood-boring insects that attack healthy trees and shrubs are called “primary invaders.” Primary invaders may eventually kill trees. Damage Borer infestations often go unnoticed until plants or parts of plants begin to die or show external signs of damage. Wood-boring insects often produce sawdust-like frass (excrement). Their holes are normally round, oval or semicircular and are found in a random pattern on the plant. Woodpecker damage is sometimes confused with that of wood-boring beetles, however woodpecker damage will not produce frass. One woodpecker, the yellow-bellied sapsucker, produces square holes in rows around a trunk or branch. Many borers damage plants by tunneling through the inner bark layer (cambium) into the sapwood (xylem) that transports nutrients and water to the leaves. These insects are called phloem feeders. When the cambium layer is completely girdled the plant eventually dies above or beyond the damage site. Partial girdling reduces plant growth and vigor above the site of attack. On occasion, tunneling makes the tree weak, causing limbs and branches to fall. Borer damage can severely affect the quality of lumber and can make trees susceptible to disease. Managing Wood-boring Insects Prevention Since most wood-boring insects are considered secondary invaders, the first line of defense against infestation is to keep plants healthy. Proper care of trees and shrubs discourages many borer pests and helps infested plants survive. Good sap f low from healthy, vigorously growing trees, for example, defends the plant from damage by many borer pests. Good horticultural practices include:

  • Selecting well adapted species of trees and shrubs that are not commonly attacked by wood borers in your area. Arizona ash, birch, cottonwood, locust, soft maple, f lowering stone fruits (such as peaches and plums), slash pines (in west Texas), willow and poplar are especially prone to borer attack.
  • Choosing and preparing a good planting site to avoid plant stress, freeze damage, sun scald and wind burn.
  • Minimizing plant stress and stimulating growth by using proper watering and fertilization practices.
  • Avoiding injury to tree trunks from lawn mowers, weed trimmers or construction.
  • Promptly caring for wounded or broken plant parts using pruning or wound paint during all but the coldest months of the year.
  • Properly thinning and pruning during colder months.
  • Removing and destroying infested, dying or dead plants or plant parts, including fallen limbs.
  • Wrapping tree trunks and limbs with quarter-inch hardware cloth spaced about 1 1/2 inches from the tree’s surface where woodpecker damage is likely.
To find more detail go to http://insects.tamu.edu/extension/bulletins/b-5086.html