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Hosta Nematode Problem

June 19, 2006

On hosta, watch for symptoms of this foliar nematode problem, which seems to be increasing in landscape settings. Foliar nematodes also appear on other perennial hosts, including anemone, creeping phlox, ground ivy, windflower, and heuchera. Nematodes are microscopic round worms that are often associated with the soil; but in this case, the nematode is a foliar nematode, occurring in the leaves. You cannot see them with the naked eye, but they are visible when observed with a dissecting microscope. Symptomatic plants exhibit brown areas between veins. Because hosta has parallel veins, the necrotic tissue gives the plant a striped appearance, as seen in the image below.

On other plants, the brown areas in the foliage may take on various shapes, usually limited by veins. This problem does not cross veins as do fungal leaf diseases or environmental scorch.

The foliar nematode is in the genus Aphelenchoides. Nematodes are pathogens much like fungi or bacteria. They require moisture to infect; they live within the plant; and they are thought to overwinter in the crown. The nematodes move in and out of the leaves when moisture is present, so they can splash from leaf to leaf with rain or overhead irrigation.

Foliar nematodes on hosta are also relatively new to Illinois landscape, and we are not seeing a big problem; but the possibility is real. Disease management is not easy. Inspect new plants for symptoms; and do not buy plants with questionable necrotic tissue. Avoid close plantings, excessively wet foliage, and overhead irrigation of symptomatic plants. Discard contaminated stock. These nematodes can survive even the cold temperatures of Minnesota, so Illinois winters are not a threat.

Author: Nancy Pataky


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