We have been receiving a few reports this season (and last year) about privet hedges shedding leaves, though we have not been able to concretely identify the cause yet. Sometimes a thrips (a type of tiny sap-feeding insect) infestation contributes to defoliation, but other sources of stress could as well. A leaf spot, if present (as we've seen with some other questions submitted),  is probably not responsible, though even if a fungicide were warranted (we do not feel that it is in those cases), it won't be able to cure an existing infection. They can only help to prevent new infections as spores land on leaves. An insecticide is similarly not recommended, both because we can't positively confirm which pest (if any) is causing damage, and because most options would involve spraying foliage, of which there is not much left to bother treating, given the circumstances. Sometimes insect-damaged foliage is more prone to phytotoxicity (plant tissue damage from chemical exposure), meaning that if it were to happen, even more leaf lesions or leaf drop could occur after treatment.

For now, it is a wait-and-see situation with regards to foregoing treatment and monitoring the plants for indications of new symptoms if or when it leafs-out again. However, since all privets are invasive plants in our region (none are native anywhere in North America, and multiple species have colonized natural areas in Maryland), we have not studied their pest and disease issues extensively, and would recommend replacement over attempts at treatment when plants decline.

If you want to keep the hedge for now, you can try rejuvenation pruning, which is the drastic removal of all branches down to about a foot or two off the ground to force regrowth. If the root system is still healthy and vigorous, regrowth should gradually fill back in. If you have a leaf blower (since the fallen foliage is too small to rake out), blow out the fallen leaves and dispose of them to avoid having them harbor any pests or disease spores by lying under the shrubs. Keep monitoring the plants for watering needs, feeling the soil about six inches deep and watering thoroughly when it becomes somewhat dry to the touch at that depth.

If you prefer to replace them, we can share ideas for replacement plants if you can provide more information about the site conditions. (For example, how much direct summer sun they get, if deer browse in the yard, what mature size they need to stay without relying on pruning, and how well the soil drains.)

Miri