Boxwood Troubles: It Might Be Nematodes

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Recently we received a sample of littleleaf boxwood (Buxus microphylla) exhibiting partial dieback of the stems and foliage, and swellings on many of the roots. Partial or sectional dieback of the foliage and branches suggests that phytophthora root rot and/or nematodes are good possibilities. In the case of this particular plant (one of several in a foundation planting), a moderate population of root-knot nematodes was identified by the NC Plant Disease & Insect Clinic and the N.C. Department of Agriculture and Consumer Services Agronomy Lab as the likely source of trouble. Management of this problem will rely on replacement with non-susceptible plant material. Ornamental grasses work well for this purpose, although due to flammability this is not the best choice for a foundation planting. The most obvious, direct replacement of the littleleaf boxwood would be dwarf yaupon holly (Ilex vomitoria), which is tolerant of root-knot nematodes. Reimagining the planting site as a herb and flower garden is another strategy. Certain marigolds are actually antagonistic to root-knot nematode populations, and other plants such as oregano and guara are very resistant to damage. Going right back in with replacement boxwoods, on the other hand, will just lead to more of the same trouble.
When landscape plants decline and die, it’s oftentimes worth the trouble to determine what happened – if possible – because this may determine whether or not you’ll have similar issues with replacement plants. Check with your local Extension office for diagnostic options.
 littleleaf boxwood

This pattern of damage, as seen recently on littleleaf boxwood, is typical of nematode damage to the roots.

boxwood roots

Up close, many of the boxwood roots were deformed and swollen, a typical symptom of root-knot nematode damage.