Salt? Not, I think, without some matching damage to the adjacent plants. The color matches an "evergreen" dead from winterkill of some sort.
As to phytophthora, perhaps. I
was thinking otherwise, but then my research found a lot of brown plants in the midst of totally green ones.
In the absence of more information from the OP, I'd say that was a decent guess.
"Symptoms/Damage
Diseased plants will commonly be found in heavy clay soils and poorly drained areas of the landscape. Affected plants will have reduced vigor and growth, yellowing of the leaves, then wilting, rapidly turning brown, resulting in death of the plant. Infected trees may decline slowly over a several year period
or they may suddenly wilt and die rapidly after the first warm weather period. Some species of Phytophthora will attack above ground portions of plants such as branches of rhododendrons or tree trunks as in sudden oak death.
"You will need to examine the root tissue several inches below the soil line. Using a knife remove the outer bark tissue to expose the inner wood. A diagnostic reddish-brown discoloration of diseased tissue with a sharp line separating the healthy white tissue will be observed. With advanced infection most of the smaller roots will have black, dead tissue and often times an unpleasant smell."
If the original poster will return and do some more diagnostics with us, we could perhaps discuss potential treatments to save the rest of the plants.
