Boxwood Disease Management: Decline, Blight, and Nematode Control

Comprehensive Boxwood Disease Management

Boxwood faces a complex of diseases including decline, blight (caused by Neonectria pseudonaviculatum), leaf burn, leaf spot, nematodes, and Volutella blight. Effective management requires accurate diagnosis and integrated cultural and chemical strategies.

Decline

Stunted growth, dieback; young foliage grayish-green/bronze/straw; old leaves fall prematurely; middle/top branch death; sunken cankers at soil line or branch crotches (dead leaf accumulation); blackened wood under cankers. Caused by multiple fungi/nematodes adding to winter injury/stress damage, especially in poorly drained sites.

Management: Protect from winter injury/stresses. Prune dead branches well below cankers. Remove dead leaves from branches.

Blight (Boxwood Blight)

Neonectria pseudonaviculatum (asexual: Cylindrocladium pseudonaviculatum, formerly C. buxicola) causes lower leaf brown spots; straw-yellow/bronze leaves falling; long brown twig lesions; white fungal growth on leaves/twigs in wet conditions; kills young propagation plants. Susceptible: Buxus sempervirens, B. microphylla (littleleaf), var. japonica (Japanese), B. sinica var. insularis (Korean), B. colchica, and Pachysandra. Long-distance spread via infected nursery material. Sticky spores spread on tools/clothing/gloves.

Management: Remove/destroy severely affected plants. Don't compost infected leaves. Thin for air circulation. Apply fungicide with thorough top/bottom leaf/twig coverage.

Leaf Burn

Leaf tips/margins yellow/redden, premature fall. Caused by water stress and low temperature.

Management: Protect from drought and drying winds in autumn/winter.

Leaf Spot

Macrophoma candollei causes straw-yellow leaves with small black fruiting dots. Only winter-injured leaves infected.

Management: Protect from wind, salt spray, salt runoff.

Nematodes

Pratylenchus causes stunted growth, bronzed leaves, decline; small roots with brown dead areas enlarging to engulf root ends.

Management: No adequate controls once infected. If removed, don't replace with nematode-susceptible plant unless site thoroughly fumigated/aerated.

Volutella Blight

Volutella buxii (asexual of Pseudonectria rouselliana) causes spring branch tip tan/straw-yellow/bronze death; pink/salmon spore masses in wet conditions; dead branches have loose bark.

Management: Dry weather: prune dead branches, thin for air circulation. Remove all dead/fallen leaves. Apply fungicide for spring/fall new growth protection. Spray for thorough leaf/twig coverage.

Integrated Boxwood Health Program

Critical practices: winter protection; drainage improvement; sanitation (dead leaf removal, no composting infected material); tool/clothing sanitation (sticky spores); air circulation through thinning; targeted fungicide applications with thorough coverage; and accurate diagnosis (blight vs. Volutella vs. decline). The introduction of boxwood blight (Neonectria) has significantly increased management complexity for this staple landscape plant.