Nematodes

Ned A. Tisserat
   Extension Specialist, Plant Pathology

Symptoms

Plant parasitic nematodes may cause significant injury to zoysiagrass, and to a lesser extent, other warm-season grasses growing in sandy soils in Missouri and Kansas. Damage usually occurs in large irregular patches scattered across the sward. This is because the nematodes have a clumped rather than a uniform distribution in the soil. Turfgrass within the patches is thin, stunted and light green to yellow. Roots may or may not exhibit blackened lesions, excessive branching, swelling or clubbing of root tips. Nematode infested turfgrass may be more susceptible to environmental stresses and other diseases. Cool-season grasses, unaffected by the high nematode populations, often colonize the damaged areas of zoysiagrass. Care must be taken in diagnosing nematode injury since other factors including soil fertility problems, temperature damage, or excessive traffic may result in similar symptoms. Soil samples should be collected and sent to a diagnostic lab if nematodes are suspected as a cause of turfgrass decline.

The detrimental effects of nematode feeding on cool-season grasses in our region have been much harder to demonstrate. For example, it is not uncommon to find high parasitic nematode populations on apparently healthy bentgrass putting greens. Recent studies at Kansas State University indicate that high populations of lance nematodes may cause subtle adverse physiological effects to creeping bentgrass, but do not result in significant reductions in turf quality. Thus, nematodes may be only one of many stress factors that are associated with bentgrass decline. Nematodes may also occur in residential landscapes and athletic fields on cool-season grasses, but are not considered to be a significant problem.

Figure 1. Spear-like mouthpart of a plant parasitic nematode is called a stylet.

Figure 2. Nematode damage to zoysiagrass fairway.

Conditions

Nematode populations fluctuate during the year. As a general rule, nematode populations are highest when turfgrass growth is optimal. However, the effects of nematode feeding may be most apparent during periods of stress. Certain nematodes are favored by light textured soils. Sand-based putting greens and alluvial soils with high sand content can harbor high nematode populations. Nevertheless, relatively high populations of certain nematodes may be found on cool season grasses in heavier textured soils. Nematode populations are reduced in compacted or poorly drained areas.

Control

Nematodes are rarely a problem in most turfgrass settings and specific control measures are not needed. High nematode populations may occasionally be found on bentgrass putting greens and on warm-season grasses in sandy soils. In these situations, damage can be masked by nitrogen fertilization. Amendments to raise the organic matter content of the soil are also helpful in suppressing nematode damage. Currently, there are no effective nematicides labeled in our region.

Web updated 9/01/06
Web comments to jpierz@ksu.edu