RE: Nematode link

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Entomopathogenic Nematodes Control Iris Borer

Iris borer, Macronoctua onusta, is a common pest of iris that kills plants by boring into the rhizomes. Eggs laid on foliage in the fall spend the winter on old leaves. In early spring the eggs hatch, bore into the leaves, often moving through stems and flower buds before they reach the rhizomes. The pinkish larvae have a brown head capsule and can be up to 2 inches long before they emerge as dull brown moths in late summer and early fall. Sanitation, or the removal of leaves in the fall does not always remove enough of the overwintering eggs to control the problem. Home gardeners and professional growers will often apply a systemic insecticide to get their desired level of control.

Research conducted at the University of Maryland indicates that entomopathogenic nematodes can control iris borer as well or better than the chemical alternatives. Commercial formulations of two nematodes, Steinernema carpocapsae and Heterorhabditis bacteriophora were used in the study along with two insecticides. Dimethoate (Cygon) was used because it is the standard insecticide used in the industry. Imidacloprid, a relatively new but popular insecticide was used because its systemic action has enabled it to provide lasting control for a wide variety of pests. The best control in the study (100%) was obtained by S. carpocapsae. Both insecticides and H. bacteriophora also provided good (87%) control.

Nematodes in this study were effective because they were applied properly. Application was delayed until soil temperature was above 50°F when nematodes are most active. Enough water was applied (1 quart/ft²) to allow the nematodes to swim close enough to the pest so that they were within their effective hunting range. Finally, the pest was in the larval stage so that the infective juvenile nematodes could enter the pest through the spiracles or anus and colonize them with insect-killing bacteria. Individuals seeking to try biological control for the first time are likely to find success with iris borer if they are given the correct guidelines.

Source:

Gill, S. A. and M. J. Raupp 1997. Evaluation of biological and chemical applications for control of iris borer. J. Environ. Hort. 15:108-110.