Plants affected
Many herbaceous plants, such as Japanese anemone (see picture), Penstemon, Chrysanthemum and shrubs including Weigela and Buddleja.
Symptoms
Symptoms are seen mainly in late summer and autumn. The foliage
becomes yellow and eventually brownish-black. In the early
stages, the affected parts appear as discrete zones bounded
by the larger veins. In time the entire leaf is invaded and
becomes discoloured. Older leaves are attacked first and then
symptoms spread up the stems. On Buddleja
there may be no obvious leaf discoloration but the flower
spikes are small and contain many aborted flowers as a result
of eelworms feeding within the developing flower buds
Cause
Microscopic nematodes or eelworms live within the foliage and buds, spreading internally between the larger leaf veins. Nematodes can spread more rapidly when the foliage remains wet, such as when there is persistent rain, heavy dew or overhead watering. Under these conditions the nematodes emerge from the leaves and spread more quickly over the leaf surface and up the stems. As the foliage dries, the eelworms re-enter the leaves and set up new points of infestation.
Control
There are no effective chemical control measures available to home gardeners. Badly infested plants should be removed and destroyed.
Eelworm-free chrysanthemum cuttings can be propagated from moderately infested plants if the material is hot water-treated first. Lift chrysanthemum stools when fully dormant and remove stems, foliage and soil. Immerse the stools for five minutes in water at 46oC (115oF), then cool them in cold water. Grow these on in clean compost and take cuttings from the subsequent growth. The duration of treatment and temperature of the water is critical; too much heat will damage the plants while insufficient allows nematodes to survive.