While most of the 25,000 species nematodes found in soils are beneficial, there are a few parasitic species that can cause crop losses. Northern root knot nematode, Meloidogyne hapla, is a major pest of some field-grown herbaceous perennials, such as Hemerocallis, daylilies (Fig. 1). The feeding of the nematodes causes wilting and plant stunting.
Figure 1. Meloidogyne hapla is a parasitic nematode of field-grown ornamental crops such as daylilies. Image on the left is a juvenile northern root knot nematode. Image on the right are adult female northern root knot nematodes in a daylily root (the pink round stains in the roots.)
As the northern root knot nematodes feed on the roots of plants, the plants form galls that can inhibit the flow of water and nutrients within the plants, cause unsightly gall development on the roots and render the plants unmarketable in bare-root sales. There are a few common methods of suppression including fumigation, crop rotation with non-hosts (monocots or grasses), hot water dips of transplants prior to planting and nematicides. However, these treatments are not sufficient and growers are still routinely losing 20 percent of their crop.
In order to reduce or eliminate the northern root knot nematodes on the transplants, the current standard treatment is dipping the rootstock in water that is 107 degrees Fahrenheit for one hour. After the hour, they are cooled down to 55 F for half an hour. However, this method can cause up to 50 percent mortality of the propagules on some varieties. Marisol Quintanilla and Kristin Poley, Michigan State University Department of Entomology, tested a variety of treatments to test if a different water temperature, dips in bleach, Fluopyram (Indemnify from Bayer), Oxamyl (Vydate from Dow-Dupont) or ultraviolet radiation would reduce or eliminate northern root knot nematodes on rootstock.