Holly Bushes- Dieback and Decline

The client was concerned about 10 year old Soft Touch hollies, that are suffering from severe dieback and decline.

DIAGNOSIS / RECOMMENDATION

Samples sent to the Virginia Tech Plant Disease Lab, which diagnosed the problem as Black Root Rot (Thielaviopsis basicola), a fungus disease. The pathogen is soil borne, so any plants showing dieback should be removed. While a preventative soil drench (1) can be used on remaining plants or new transplants, consideration should be given to planting a different species that is not susceptible.

ADDITIONAL INFORMATION

Although Japanese holly (Ilex crenata) is a popular broadleaf evergreen in Virginia landscape plantings, dieback is a common complaint. The most common cause of dieback in Japanese holly is the root disease, black root rot, which gets its name from the masses of black fungal spores that form in and on infected roots. Japanese holly is especially susceptible to this disease; however, some other hollies, such as Ilex glabra (inkberry), I. x merserveae (Meserve holly), and I. opaca (American holly) can also be affected. English holly (Ilex aquifolium) and Chinese holly (Ilex cornuta) are highly resistant (3). Note that it is also advisable to avoid planting pansies, petunias, phlox, annual vinca, coral bells, and zinnias in soil where black root rot has been diagnosed because these herbaceous plants are also susceptible to the disease (2).

Plants initially turn off-color, but sections of the plant gradually turn brown, and eventually the whole plant dies. (2) A diagnostic sign is the blackened areas on the roots, which include the fungal spores (2). Plants with extensive root rot damage will usually decline and die during dry periods (4).

Virginia Tech has provided a Youtube video to provide additional information on this common disease in hollies (5).