Wednesday, June 25, 2008

Landscape and Nursery - Foliar Nematodes

Plant parasitic nematodes are microscopic worms that are usually found in the soil attacking plant roots. There are some nematode species, however, that can cause damage on aboveground plant parts. The following is some information on these pests.

Foliar nematodes (Aphelenchoides spp.) have become a more common pest in herbaceous perennials over the past few years. Foliar nematodes move in films of water on plant surfaces and enter leaf tissues through natural openings in leaves called stomates. Like root-attacking nematodes, foliar nematodes have a needle-like structure called a stylet that they use to pierce plant cells and feed on the cell contents, resulting in cell death. Lesions caused by foliar nematodes are first chlorotic, then necrotic. Movement of the nematodes within leaf tissues is restricted by larger leaf veins, which gives the lesions their typical angular shape (see figures).

Foliar nematodes overwinter in plant debris. They survive for long periods of time in leaf tissues, and are spread by propagating infested plants and by splashing water (rainfall, overhead irrigation). The list of plants susceptible to foliar nematodes is quite large, and includes woody plants like azaleas as well as numerous herbaceous perennials (such as chrysanthemum, hosta, hellebores, ferns, begonias, salvia, anemone). The easiest way to manage foliar nematode problems is to avoid introducing the pest into the garden. Carefully inspect plants for foliar nematode symptoms before planting. If symptoms develop, remove and destroy affected plants.

Premature dying of foliage in the garden is symptomatic of foliar nematode but is easily overlooked or misidentified. Constant leaf wetness helps nematodes as they swim in a film of water and enter the leaves through stomata. Remove infected leaves and destroy them. We still do not have any effective chemical controls for the home or commercial landscape.

Information from Karen Rane, Plant Disease Diagnostician, Department of Botany & Plant Pathology, Purdue University and Bob Mulrooney, Extension Plant Pathologist, UD.

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