Lowering ph around mature dogwood
We have a mature Dogwood that is looking stressed. We think it's due to a number of factors including some significant leaf loss from last spring's hailstorm. But we also ran a soil test and found that the ph is higher than dogwoods prefer. Close to 7.0. The level of phosphorus Is also low. If we used elemental sulfur to top dress this area, how much should be used, when should it be applied, and where? Should I follow the drip line?
Montgomery County Maryland
A flowering dogwood can tolerate a pH range of 6-7. According to the soil test the pH is within the range and we do not recommend lowering the pH.
When subject to drought, poor planting techniques, poor soil drainage, excessive mulch, etc. the trees can be susceptible to insect and disease issues.
Dogwood trees are susceptible to numerous problems. Most of the diseases are evidenced by discoloration of the foliage such as powdery mildew, spot anthracnose, and cankers. Boring insects - look for cracked bark along the base of the tree. The tree is already suffering by the time you see the symptoms. You can look for this.
See our publication on dogwood for more information http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG12_IPM_Series_Dogw...
You can send us digital photos of the tree, around the base of the tree, and affected foliage so we can see what you may be dealing with.
In general, mature trees do not require fertilization. The soil test report should have indicated how much phosphorus to apply, if low.
Photos are attached. We have only lived in the house for one year, so we don't know much about the history of the tree. However, we have seen some branch die-back in the outer and upper extremeties of the tree and significantly smaller leaves this year than last.
Your dogwood has powdery mildew, which is a very common problem in these trees. It can be present all through the summer and it reduces the vigor of the tree, resulting in symptoms such as smaller leaf growth. It also looks like there is a problem at the base of the tree trunk. Dogwoods are susceptible to boring insects and cankers. This type of damage can result in branch dieback. https://extension.umd.edu/hgic/cankers-trees-and-shrubs
The powdery mildew will likely be a persistent problem. Chemical control of the pathogen would require spraying at bud break an regularly all season. Most people don't want to do this amount of maintenance. There are some powdery mildew resistant varieties that are starting to come onto the market, but they are difficult to find.
The best you can do is keep the tree watered during very dry periods and prune out any branches that die back. You can also apply a thin layer of mulch at the base of the tree (no more than three inches and don't put it directly against the trunk). This will help to conserve moisture and will also provide some additional nutrients as the mulch breaks down. There is no need to add any additional fertilizer.