Surface roots compete with the lawns and ground-cover plants for moisture. As the tree gets larger, the other plants don't get enough light in the shade of the tree and they die from lack of water and light. With fewer plants protecting the soil, it will erode away when there is wind or rains, further exposing the roots.
Replacing the soil is OK to level things off and adding mulch helps to keep it from eroding. The problem comes when too much soil is added on top of the roots. They are growing at the surface where they can get oxygen, so adding more than six inches of soil will have a good chance of killing the roots. Heavy, thick mulch will compound the problem. Don't install any soil or mulch against the tree trunk.
If you add soil but don't protect it, it will erode away again. After adding the soil and mulch, plant a ground cover and keep it watered until it is growing well. Don't use grass, as it needs too much light to grow well under a tree.
Q: We live in South Florida and our St. Augustine lawn was recently diagnosed with "take-all patch." We would like your opinion about how to go about treating this problem. We have lost some large patches of grass. We have an irrigation system but did not use it frequently during a dry spell last winter (due to the high cost of city water). Could this have affected the lawn? Should we treat it chemically first or remove the dead areas and re-sod? We also have a Labrador retriever, who is often on our lawn, so we don't want to treat with chemicals that could hurt him.
A: If this was an accurate diagnosis, you will have some tough work ahead of you. There is no simple effective chemical control for this disease. What lawn care have you done recently? Have you applied lime? Does the lawn have compacted soil? Has the lawn been aerated recently?
This disease tends to form on grass growing on soil that has a high pH, that is compacted and over-watered or has poor drainage for when it does get watered. Using an acidic fertilizer will help lower the pH. Doing a core aeration will help relieve compaction and help with the drainage. Further work may need to be done with the drainage. The core aeration should have cores taken every 2 to 3 inches apart and as deep as possible, but not less than 4 inches deep.
All of the dead areas should have the grass and soil removed a couple of inches deep, being sure not to spill it on healthy grass. This disease comes in during cool fall weather and the symptoms don't show up until the weather turns hot and dry months later. I don't think your restraint on watering last winter had any effect. To prevent further spread this fall, you may want to spray the lawn with a fungicide.
Q: I planted a Bartlett Pear tree fifteen years ago. It is 20-25 feet tall and has a great rounded shape. It is close to perfect in this regard.
My question is as follows. Beginning in June about one-third of the leaves on the north side of tree developed only a light-green color. The remaining two-thirds of the leaves are bright green. May this signal a problem? I would imagine the root system would develop outwardly as the tree grows, so is there a missing ingredient(s) that I can add on the surface that may help?
A: Even though the roots and top do connect in a mostly regular fashion, the trunk has enough sideways connections spreading water and nutrients around the tree that I don't think this is going to be a soil problem.
Follow the branches with the off-color leaves back toward the trunk and see if they all go to a single origination point. My suspicion is that there is a point where the branch or trunk has been damaged. It could be from all kinds of manmade or natural sources. It may even be that the tree has constricted a branch with other branches, which is common on pears that have a lot of parallel trunks growing side by side. If you can find a hole, crack or other obvious problem, let me know and we can deal with that. (Pictures will help.)
If you can't see any source of the problem, a licensed arborist may be necessary to look at the tree with a trained eye.