Answer: Based on your description I am not certain what is happening to your rhododendron. The browning could be due to winter damage and/or oscillating spring temperatures. New plants, and especially plants set out in the fall, are most susceptible to this type of damage. If there is healthy new growth, then I would suspect winter damage.
If the new growth is also affected, then it may be a disease problem such as a root rot. A disease is more likely to occur if the plant is growing in heavy clay type soil or in a poorly drained location. If you think this is a possibility, I would suggest you consult with your local Rutgers county extension to obtain a more specific diagnosis. They may appreciate an overall photo of the plant plus closeups of the affected foliage, and/or a freshly cut foliage sample enclosed in a clear plastic bag and kept cool so it stays fresh. Based on knowing their diagnosis, you can decide what to do. If a chemical control is needed, they will have the most up to date information on what to use, how and when is best to apply it for maximum results.
In the meantime, keep the soil evenly moist like a wrung out sponge, not sopping wet/saturated and not dried out. Use your finger to check the soil and see if you need to water.
Also use an organic mulch such as pine bark over the root area year round. Spread the mulch out in a flat layer to a depth of about two inches. Do not allow the mulch to touch the stems of the rhododendron. This will help keep the soil more evenly moist and will help feed the soil slowly as it breaks down.
Good luck with your rhododendron!
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