What is the clear sticky substance dropping from my emory oak tree?
Our emory oak trees are dropping a clear sticky substance, when on the ground looks like little pieces of glass. What is it? It sticks to the feet of our dogs and then little stones stick to that - it is a big mess.
It sounds like the sticky substance is honey dew that is excreted in large volumes from the kermes scale. Kermes scale are tan, globular, and hard. They are easily mistaken for galls or buds. Oak is the only host. This species is not particularly injurious to host trees, but, if necessary, treat crawlers between late May
and mid-July or use a dormant oil in April.
Scale insects feed on plant sap. They have long, threadlike mouthparts that are six to eight times longer
than the insect itself. Scale feeding slowly reduces plant vigor; heavily infested plants grow poorly and may suffer
dieback of twigs and branches. An infested host is occasionally so weakened that it dies. Scales often secrete a sticky honeydew that is attractive to wasps and ants and which supports the growth of black sooty molds.
Scale insects are generally controlled by natural enemies, including tiny parasitic wasps and predators such as ladybugs. It is
very common for ladybugs to move onto a plant with a growing scale infestation. Before deciding on a treatment, look for adult
and immature ladybugs on plants. Dormant oil treatments can be used against almost all scale problems and are generally applied in
very early spring, before bud break. Summer oils can also be very effective against most scales, but as with dormant oils, some plants are
sensitive to these treatments. Check labels to make sure the plant is not harmed by the treatment being considered. Most other
insecticides, including insecticidal soaps, can be used only against the mobile crawler stage of scales since adult scales are protected from
insecticides by a waxy covering. These treatments are very effective, but must be carefully timed as crawlers are only active for a
You may have to look closely at the tree to see if you find scale.