Spiral Nematodes

Nematodes can be a threat to turfgrass, and have been found in golf courses, parks, and lawns in the San Francisco Bay Area. Spiral nematodes (Helicotylenchus spp.) are one of many nematode species that are found in the soil. Spiral nematodes have a wide host range, and do not cause excessive damage, but they can reduce the vigor of plants in a monoculture host like turf grass. Mature spiral nematodes are up to 1.2 mm long, and are so named because they curl up into a spiral when dead or relaxed. They are ectoparasites, meaning they feed outside the cell, although some may act as partial endoparasites—inducing growth of a food cell in which they bury their head to feed for long periods of time, before moving on to create a new food cell. These food cells do not grow like a gall, but the cell composition does change.

Spiral nematodes are all females, reproduce without mating, and lay individual eggs in the soil (unlike the root rot nematode that lays an egg mass). The first molt occurs within the egg (J1). If moisture is present in the soil when the egg hatches (J2), the nematode is motile and works its way to a plant root where it can feed. The nematode undergoes three more molts (J3 and J4), before becoming a mature adult. Populations are highest in late summer and early fall and lowest in spring when cold temperatures inhibit reproduction.

Spiral nematode turf damage is associated with bluegrass and Bermuda grass. Above ground symptoms include stunting, reduced plant vigor, yellowing or brown patches in the turf, and areas that succumb to weeds. There is typically a “hot spot” or dead zone, which is heavily infested. These symptoms can have other causes, so soil analysis is required to diagnose the problem: http://youtu.be/taW-VM-4IRw

For management tips, see the Integrated Pest Management(IPM) site. Prevention is the best approach, but strategies like crop rotation are difficult for turf. Chemical treatments exist, but some of them cause damage to turf, or must be repeated, since they also kill beneficial organisms that keep other diseases at bay. See UC IPM Pest Management Guidelines: Turfgrass (page 72) for additional information.