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California Gardening

Sticky substance on leaves of Red Oak

17 years ago

We see a sticky substance on the leaves of our Red Oak. We think it is a disease of some kind - bees like the leaves, the sap from the leaves fall on cars parked underneath. We live in Sacramento and my husband thinks there should be some kind of spray so that this substance doesn't kill the tree. On occasions (not presently) I have noticed lots of ants on the trunk of the tree. However, our tree is about 35 feet high. What is this sticky substance? What do we do to help this tree - and how do we reach the tall leaves? Or do we not do anything until all the leaves fall off during the winter? What are the consequences if we did nothing? As you can tell, we are in a quandary about how to help this tree. Thanks in advance for your assistance.

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Comments (3)

wanda
17 years ago
Have you checked the tree for scale insects or aphids?
The sticky substance may be honeydew (a secretion from these insects). Seeing ants is another indication that this might be your problem as ants "farm" these insects to gather the honeydew. If honeydew is left on the leaves, you might start seeing a black sooty substance, known as "Sooty Mildew" on the leaves. This is the byproduct of decaying honeydew.

If aphids or scale is your problem, you can spray with a hose end sprayer and insecticide of your choice (horticultural oil, soap spray, malathion, etc.)

wanda
bryce5
Original Author
17 years ago
Thank you Wanda. Yes, there are some black substances on the leaves. How would we spray the leaves that are towards the top of the tree, esp. since it is so tall? What happens to the tree if insecticide wasn't used - would these scale insects hurt the integrity of the branches, tree? As you can tell, I don't know much about gardening; and I really appreciate yours and any other's advice.
Tahnk you.
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I've seen extensive damage to branch tips on a wide variety of trees due to squirrels. That's another possibility for you to consider. Nandina, do you remember the huge 'epidemic' of squirrel damage to the live oaks in Beaufort? Everyone (including me, probably) was convinced that it was some kind of fungal infection until Michael Murphy started investigating. It was a drought year, and the squirrels had been BUSY!!! I don't have any good ideas about the icky stuff dripping from the tree. I do not, however, think that it's from spittlebugs. I disagree with Ken that trees can withstand most anything that comes their way. Urban trees face circumstances that can set them up for failure, infestation, and infection. Such factors as compaction, street and sidewalk construction, poor soil, vehicle emissions, some street lighting, and an assortment of other 'trials and tribulations' can each (or all) take chinks out of a tree's natural armour. If these trees are valuable to you in terms of shade and/or added property value, I'd seriously consider finding a couple of ISA (International Society of Arboriculture) Certified arborists to come out for an evaluation and estimate on any needed work, if required. You might even be lucky and find that there is a well-informed certified arborist at your local extension office. That would be worth a phone call.
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wanda
17 years ago
Did you determine that it was definitely scale and not aphids?
Aphids are a less serious threat, esp. if your tree is deciduous. You could just try blasting off the aphids with water spray and putting tanglefoot around the base of the tree to keep off the ants.

If it is scale, then they are much harder to get rid of and pose a more serious threat. If the tree is too large to spray, then it might be more prudent to try a systemic that you water into the tree.

wanda

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