Greenhouse and Nursery - Foliar Nematodes

It is important to check overwintering plants in greenhouses and nurseries for signs of diseases. The following is a good article on foliar nematodes in overwintering perennials from the University of Maryland.

Your herbaceous perennials are tucked into overwintering houses in February and you may not be giving much thought to pests on your plants. We thought so also until last week when the UMD Plant Diagnostic Lab received samples of heuchera with leaf spots on the foliage. These symptoms could easily be mistaken for a fungal leaf spot disease. Turns out it was not – it was foliar nematode. These microscopic roundworms move in films of water on plant surfaces and enter leaf tissues through 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 cell contents, resulting in cell death.

Lesions caused by foliar nematodes are first chlorotic, then necrotic. Early symptoms can appear as small speckles or spots, which look very similar to fungal leaf spot diseases or chemical injury. Movement of the nematodes within leaves is restricted by larger leaf veins, resulting in necrotic lesions with an angular shape.

Foliar nematodes overwinter in plant debris, or on infected perennial plants. They survive for long periods of time in leaf tissues, and are spread by propagating infected 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 hosta, heuchera, hellebores, ferns, begonias, salvia, and anemone).

The easiest way to manage foliar nematode problems is to avoid bringing them into your facility. Carefully inspect new plants for foliar nematode symptoms. If symptoms develop, remove and destroy affected plants. Pylon is registered for controlling foliar nematodes, but this treatment will only knock down populations, not completely eradicate them. Sanitation is key to keeping this pest in check.

Heuchera with small lesions on foliage caused by foliar nematodes. Photo by Selin Balci.

Article reprinted from the February 6, 2009 issue of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension Central Maryland Research and Education Center.