Figure 5. Galls produced by root-knot nematode on roots
of Japanese holly cv 'Helleri'. (Courtesy of R. Jones, North Carolina State
University).Nematodes are microscopic worms that feed on the feeder root system of plants. Generally, damaging populations of these pests are limited to sandy or sandy loam soils. Several species of the root-knot and ring nematode are know to attack Chinese and Japanese holly. Serious nematode damage on holly is rarely seen in the landscape, though some damage is sometimes seen on field-grown holly. Generally, container grown holly will be largely free of damaging nematodes.
Typical symptoms of nematode injury such as yellowing of the leaves, slowed growth, and poor response to fertilizers or irrigation usually don't appear until the roots have been badly damaged. Damage related to poor soil fertility, improper plant establishment, drought, and similar disorders can easily be mistaken for nematode injury. On root-knot damaged holly, numerous, small galls or swellings will appear on the feeder roots (Figure 5).
Figure 5. Galls produced by root-knot nematode on roots
of Japanese holly cv 'Helleri'. (Courtesy of R. Jones, North Carolina State
University).
Often, established hollies will tolerate some nematode damage without any noticeable injury to the plant.
In the landscape, a little planning will go a long way towards minimizing the risk from nematodes. Since damaging nematodes are most likely to occur in the soils of old vegetable gardens, a nematode assay should be run on soil from these areas before any plants are established. Before planting any field for balled and burlapped (B&B) holly production, a nematode soil assay should be run. If root-knot or lesion nematode are found in landscape beds, plant a holly cultivar resistant to that nematode. In field nurseries, do not plant holly in those fields known to be infested with damaging nematodes.
The yaupon and 'Burford' Chinese holly are resistant to the ring nematode while cultivars of the Japanese holly are not. The 'Burford' Chinese holly is, however, sensitive to attack by the southern root-knot nematode, the most common nematode pest of vegetables and ornamentals. The reaction of other hollies to plant parasitic nematodes is largely unknown. Additional watering, mulching, and fertilizing to need may improve the health and restore the beauty of nematode-damaged plants. Adding compost to landscape beds may also help plants recover from nematode damage. Severely stunted plants will rarely respond to better care and should be replaced with a nematode resistant plant. See Extension Circular ANR-689, "Nematode Pests of Flowers and Woody Plants," for more information on nematode resistant woody plants.
Holly fanciers and nursery operators should not propagate holly in non-sterile field soil. Preferably, holly cuttings should be rooted in a bark mix using the same precautions already described under Pythium and Phytophthora root rot control. If field soil is used, make sure that it has been heat or steam sterilized. Avoid rooting cuttings in ground beds, regardless whether or not the soil can be sterilized.