Nematode Damage on Woody Ornamentals: Symptoms, Diagnosis, and Management

Nematode eggs.

Biology

Nematodes are soil-dwelling non-segmented roundworms, usually <0.5 mm (0.02 in.) long. Plant-parasitic species have a hollow spear-like stylet pushed into plant cells. Enzymes forced through stylet digest cell contents, which are drawn back into nematode's digestive system. Life histories and longevity vary greatly. Some live inside host tissue, produce 2+ generations/year; others live outside feeding on outer layers, 1 generation/year. Egg production varies from hundreds to few per season.

Genera causing damage on woody ornamentals: Meloidogyne (root knot), Criconemella (ring), Pratylenchus (lesion), Tylenchorhynchus (stunt), Paratrichodorus (stubby-root), Rotylenchus (reniform), Xiphinema (dagger). Often multiple species on a plant's roots; effects of mixed populations largely unknown.

First determine if problem is due to nematode activity. Many unrelated factors cause similar symptoms.

Symptoms

• Plant decline over several seasons.
• Chlorosis resembling iron deficiency.
• Foliage bronzing (characteristic of boxwood).
• Foliage death and drop.
• Branch dieback.
• Root systems small with necrotic/galled areas.
• Plants stunted.

In nurseries, symptomatic plants occur in scattered clumps. Nematodes may be in nursery soil, spread by tilling, soil movement, runoff. Can be introduced on rooted plants.

Management in Nursery

Field

Fumigate planting area with registered material before planting. Plant nematode-free material.

Containers

Use sterile potting mix. Avoid contaminating mix with untreated soil. Plant nematode-free material.

Management in Home/Commercial Plantings

• Plant nematode-free material.
• Known infested areas can be fumigated before planting.
• Post-plant chemical treatments by homeowners not recommended. Remove severely affected plants. Mildly affected: water, fertilize, protect from other stresses.

Xiphinema (dagger nematode) with stylet protruding; new stylet forming below. At molt, nematode loses stylet and must replace it.

Host susceptibility table (from Jones, Benson, Barker 1982, NCSU): HS=Highly Susceptible; S=Susceptible (some stunting but satisfactory growth); T=Tolerant (satisfactory growth); ?=Not tested.

Host Plant	Root Knot	Stunt	Lesion	Ring
Azalea	T	S	?	T
Aucuba japonica	HS	S	?	T
Buxus microphylla (Japanese Boxwood)	HS	T	?	?
Buxus sempervirens (American Boxwood)	?	T	?	?
Buxus sempervirens (English Boxwood)	?	?	HS	?
Camellia japonica	T	T	?	?
Camellia sasanqua	T	T	?	?
Gardenia jasminoides	S	T	T	T
Gardenia radicans	HS	T	T	T
Ilex cornuta (Chinese Holly) cv. Burfordi	T	T	?	T
cv. Rotunda	S	S	?	S
Ilex crenata (Japanese Holly) cv. Compacta	HS	T	T	S
cv. Convexa	HS	T	?	S
cv. Helleri	HS	S	?	S
cv. Rotundifolia	HS	S	?	S
Ilex vomitoria nana (Yaupon Holly)	T	T	?	T
Juniper sp. cv. Blue Rug	T	T	HS	T
cv. Shore Juniper	T	T	?	T
cv. Spiney Greek	T	T	S	T
Ligustrum (Privet)	T	T	?	T
Nandina domestica	T	T	T	T
Photinia fraseri (Red Tip)	T	T	?	T
Rose	S	S	S	T

Prepared by Gary W. Moorman, Professor of Plant Pathology.