Phytophthora

a form of water mold that infests the roots of plants and destroys root tissue; caused by poorly-draining soil and overwatering; frequently found on ornamentals and plants surrounded by mulch with low levels of aeration; can live in soil for extended periods without host; identified by branch die-back, reduction in shoot growth, small leaves, and thinning crowns; diseased roots are reddish-brown and brittle