Answer: Rhododendrons are very sensitive to any kind of root disturbance. They also appreciate having shade at their roots to help keep the soil cool and moist. So you may have disrupted the rhododendron during the clean up, especially if you used any type of herbicide beneath it or around its perimeter.
On the other hand, this past winter/spring was very difficult for many plants due to the oscillating temperatures and uneven precipitation. This may have stressed your plant as well.
Finally, there are a number of insect and disease problems that can affect a rhododendron and they are more likely to affect a plant that is stressed than one that is not stressed.
I would suggest you consult with your Rutgers county extension and see if they can help you diagnose the dieback more specifically and based on knowing that, determine what to do for it. Good luck with your rhododendron!
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