Dying French Lilac

Question

I live in South East Tennessee. About 7 years ago I planted two Lilac bushes in my front yard. One is the regular purple kind, the other is called a French Lilac.

The purple one started to get too congested in the middle, so I cut out all the middle branches that looked dead. I also started getting Kudzu growing around it. This year it is doing better.

The French Lilac looks like half of it is dead and I don't know what to do. I planted both of these bushes the same year, but one is huge and the other is only half as tall as it was when I planted it. Maybe it is supposed to be that way?

I cut some of the branches down and the sucklings at the bottom. Now what?

It is planted in what became a low spot in my yard after having my yard dug up to have pipes from house to sewer replaced. They just filled in the yard and planted grass seed. It is no longer level. Could it be the drainage?

There is a greenish white spot where the stem meets the tree.

Answer 1

OP appears not to have revisited in just under a year and even some of the images provided at one time are no longer available so to patch together what facts we do have:

1. Terrain level has been effected by laying of replacement pipe – in particular, the location is now a low spot.
2. The tree was sold as French Lilac, so is presumably a Syringa vulgaris, since Galega officinalis, which shares the same common name, is a herbaceous plant.
3. It started getting Kudzu growing around it.
4. Kudzu seeds will successfully germinate only when soil is persistently soggy for five to seven days.
5. Kudzu modify the relative pore distribution in soil and hence freeing for plants even more water than in the original soil.
6. There is a greenish white spot where the stem meets the tree.
7. In late summer, lilacs can be attacked by powdery mildew, specifically Erysiphe syringae, one of the Erysiphaceae. Also: Microsphaera syringae is a fungus that can cause powdery mildew in lilac. (This is the same taxon as Erysiphe syringae.)
8. Powdery mildew causes leaves to fall off and the shrub to look unattractive.
9. Once established, lilacs only require occasional watering.
10. In the first picture (though not the second) the smaller lilac appears to be partially shaded by the larger.

When there is more rain or humid conditions we see more powdery mildew on our plants. The sudden change from wet or humid conditions to warmer, dry temperatures are perfect conditions for this fungus to grow. Warm temperatures and shady conditions encourage the fungus to grow and spread.

It seems at least plausible that the leaves have been shed in response to an attack of powdery mildew, brought about by an increase in soil humidity, probably attributable to the groundworks for the sewer replacement, and that poor drainage has contributed to poor growth (stunting) of the bush.

Application of Miracle-Gro may be exacerbating matters with the added nitrogen encouraging tender, and more susceptible, leaf growth.

There does not appear to be room within the property boundary for a sump at a lower elevation but one at the same elevation might alleviate the problem.