Native Plants

Q. Who is Mr. Smarty Plants?
A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.
Did you know you can access the Native Plant Information Network with your web-enabled smartphone?
Ask Mr. Smarty Plants
Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

rate this answer

Friday - September 19, 2008
From: Foristell, MO
Region: Midwest
Topic: Trees
Title: Sappy dew killing plants under oaks in Missouri
Answered by: Barbara Medford
QUESTION:
There is a sappy dew killing my perennials.I have several large oaks in my yard. I had different kinds of shade perennials around each base of the trees. But as years have gone by, the different varieties of perennials would eventually die out; as well as any grass under the tree out to the drip line. I was told that the oak trees produce a sappy dew to kill anything under the tree that would threaten the tree's nutrients. Is this true? What can I do to get my beautiful perennials and grass back under the trees?ANSWER:
There are five oaks that are native to Missouri, and we are assuming your oaks are one of these: Quercus alba (white oak), Quercus bicolor (swamp white oak), Quercus macrocarpa (bur oak), Quercus palustris (pin oak) and Quercus rubra (northern red oak). While the acorns and young leaves of oaks are usually mildly toxic, none of these were indicated to be very allelopathic. Allelopathy involves a plant's secretion of biochemical materials into the environment to inhibit germination or growth of surrounding vegetation. Allelopathy enhances tree survival and reproduction. In other words, the plant is protecting itself, its nutrition and water sources, as well as its space, by inhibiting other plants in competition with it.
We are inclined to believe that the failure of your grasses and perennials are more to be attributed to the shade of the oak, and the fibrous root system. Roots of oaks will often extend far beyond the drip line of the tree itself, and the majority of tree roots are in the upper 6 to 12 inches of the surface of the soil. Also, leaves of deciduous trees can accumulate and smother emerging plants, or promote mold and fungus diseases. Most grasses have difficulty in surviving in that environment, as well as flowering plants; the biggest disadvantage being the amount of shade cast by the mature oak. Basically, you will have to make a choice - big oaks providing shade for the property or flowering perennials? There are shade plants that can be planted under an oak, mostly low groundcovers, but even they have trouble competing.
So, back to the sappy residue you are experiencing in your yard. This sounds a whole lot like aphids, which generate a substance called honeydew, that will drip on lawns, houses, cars and people. It also can cause a sooty mold on the leaves and be very unattractive. This Colorado State University Extension article on Aphids on Shade Trees and Ornamentals will give you some information. They usually are not harmful, and you should avoid pesticides, which are more likely to kill the predators of the aphid than the aphids, themselves.
More Trees Questions
Is bald cypress native to Dallas area?
September 19, 2009 - There are 2 very large bald cypress trees growing beside one another at a park in North Dallas, and I was wondering if they were native or planted a long time ago by the settlers or something. They ar...
view the full question and answer
Shade tree for Southern California
November 14, 2013 - I had to cut down my huge ficus tree for several reasons, however it provided lots of shade, that we miss. Can you help me find a good shade tree with non-invasive roots that is good for growing and p...
view the full question and answer
Tree transplants having problems in Manchaca TX
April 03, 2010 - I have recently transplanted a Mexican Buckeye, Chinquapin oak, and Sandpaper tree that I have been raising inside since they were seedlings. They have now developed a browning of the tips of their l...
view the full question and answer
Chlorotic disease in scrub oak from Katy TX
July 04, 2013 - Please tell me how to treat my scrub oak as it has chlorotic disease. Parts of the tree are fine and others have yellow leaves. It has not been injured in any way.
view the full question and answer
Causes of death to Papershell pinion pine (Pinus remota)?
December 03, 2015 - Good afternoon. I did my best to review the site and have not found a comparable question - apologies if I have missed something. I own property equidistant between Leakey and Campwood off of HWY 33...
view the full question and answer
Support the Wildflower Center by Donating Online or Becoming a Member today. |