Lilac bush and dogwood turning brown
I planted a new dogwood tree in full sun in the front yard. It wilted almost immediately. I may have overwatered in response . It now has mostly brown leaves. I also planted a new lilac bush this spring the backyard that had something that looked like powdery mildew. I sprayed it with neem oil and the leaves started turning brown and dying. Was it a fungus that I did not treat suffiently? Was this the neem oil? Should I dig up the dirt when it dies as it seems to be trying to do? Thanks in advance.
We viewed your photos. You have several issues that you may be dealing with.
Lilac - You may be dealing with poor planting techniques watering issues as well as powdery mildew, a fungal disease. This fungal disease is usually not lethal to lilacs, but is certainly not attractive. Control begins by selecting powdery mildew resistant varieties. There are different species of lilacs and the reblooming lilacs (Bloomerang series) that are resistant.
Check the label registration on horticultural oil products for powdery mildew control listings. If severe, you can spray once a month as soon as you notice the mildew. However, this disease will not kill the plant and you do not have to spray. Make sure there is good air circulation and is located in full sun. http://extension.umd.edu/hgic/powdery-mildew-trees-and-shrubs
Neem and horticultural oil can subdue the mildew. It will not control anything that is already there. Do not spray in high temperatures. This can affect the foliage.
Be sure to keep the shrub well watered during dry periods. Check the soil moisture at least once a week up until the ground freezes. Make sure mulch is no thicker than several inches and away from the base of the shrub. The shrub is struggling to establish itself. Make sure it is not planted too deeply. See the publication below. Scratch the branches with your fingernail and look for green tissue. If you see it, then it is still viable.
Dogwood - Wilting can occur if plants are under or overwatered. The tree also looks like it may have been planted too deeply and there is too much mulch around the base of the trunk. At this point, remove the excessive mulch from the base of the trunk. Mulch should be no thicker than several inches and keep away from the base of the trunk. You should be able to see the flare at the base of the trunk where it joins the root system. If not visible, then the tree may be planted too deeply. If so, you can carefully remove the soil from the circumference of the trunk to the point where the trunk flares out into root growth. See our publication on this http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG86%20Common%20Abio...
Check the moisture once a week up until the ground freezes. Soil that is moist is fine. You may need to probe with a screwdriver. In general, dogwoods grow best in morning sun and afternoon shade. In full sun, they will need more moisture in dry periods. Here is our dogwood publication http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG12_IPM_Series_Dogwood.pdf
and our Planting Process for trees and shrubs http://extension.umd.edu/hgic/trees-and-shrubs/planting-process