Nematodes are microscopic worms that can have a significant impact on the health and vitality of turfgrass. They are plant-parasitic organisms that inhabit the soil and feed on the roots of turfgrasses. In the process, they cause damage to turfgrasses that affects overall growth and vigor. Nematode infestations can lead to symptoms such as chlorosis, lack of turf vigor, and restricted root development.

Accurate diagnosis of nematode problems requires careful sampling and analysis of soil and root samples. Understanding nematodes and their effects on turfgrass is crucial for effective management and maintaining healthy turf ecosystems.

Credit: PACE Turf

Causal agents

Plant-parasitic nematodes are microscopic roundworms that are obligate parasites of plants. They have complex internal organs that change throughout the nematode lifecycle. Nematodes use stylets, which are spear-like mouthparts, to penetrate plant cells and extract nutrients.

There are various genera and species of plant-parasitic nematodes that can affect turfgrasses. Some commonly reported genera of plant-parasitic nematodes on turfgrasses are listed in Table 15.6.1. The common names of these nematodes are based on their shapes, anatomical characteristics, or the symptoms they cause in plants. Taxonomy of nematodes can be complex, and modern diagnostic techniques are used to distinguish certain genera and species.

Nematodes found in turfgrass systems exhibit different feeding modes:

• ectoparasitism – feeding on the outer surface of plant roots
• endoparasitism – feeding inside plant roots

Appropriate management strategies must take feeding mode into account in order to minimize the damage caused by nematodes in turfgrass systems.

Primary Hosts

Plant-parasitic and saprophytic nematode species of diverse taxa are normal components of turfgrass ecosystems and are commonly present at high population densities in soil. Nematodes cause extensive losses in turfgrasses in warm temperate and subtropical regions and chronic debilitation of grasses in cooler regions. 

Disease Cycle

Nematodes have life cycles similar to insects. Females lay eggs that hatch into juveniles. Juveniles molt through four stages to become adults. Fertilization is required for reproduction in most species. Nematodes survive as eggs in the soil and become active when conditions favor turfgrass growth. They can spread through water runoff or infested soil/sod. Nematodes damage turfgrass roots, and coexisting pathogenic fungi can worsen the damage. The fungi thrive when plant fluids leak into the soil, causing more severe diseases. Identifying the primary cause of disease becomes challenging when multiple pathogens interact.

Epidemiology

Nematode activity is favored by optimal soil temperatures and moisture levels. Thatch provides a suitable environment for nematode proliferation, while dry or saturated soils restrict their activity. Compacted or heavy-textured soils are less favorable for nematodes compared to lighter soils. Cool-season grasses are most susceptible to nematode damage in spring and autumn, while warm-season grasses are affected during the active growth periods. Sting nematodes migrate below the root zone as soil temperatures rise, while root-knot nematodes remain in the upper soil layers. Symptoms of nematode feeding become prominent during unfavorable conditions and stress periods.

Symptoms

Nematode damage in turfgrasses shows symptoms resembling stress, including chlorosis, declining growth, thinning, wilting, and even death. These symptoms can be uniform, or they can appear as dispersed patches. Nematode damage is more severe under stressful conditions and can increase turfgrass susceptibility to fungal pathogens. Roots may exhibit reduced growth, lesions, swellings, or knots.

When aboveground symptoms persist despite proper management practices, nematodes should be considered as a possible cause. Additionally, if turf does not respond to soil aeration, nematodes should be suspected.

Signs

Nematodes are often difficult to identify, so a trained professional should be consulted. To accurately diagnose nematode problems, a nematode assay of soil and turf root samples is necessary. Diagnostic laboratories have specific procedures for collecting samples that fit their nematode enumeration method, and turfgrass managers should consult laboratory websites for the most up-to-date information on sampling techniques. It is important to collect samples from healthy turf or the perimeter of damaged turf, as severely damaged turf may not provide accurate analysis due to the biotrophic nature of nematodes. Developing a relationship with a single laboratory for analysis is recommended, as different laboratories may have varying preferred techniques and threshold values.

Nematode populations can vary significantly across turf plantings, so breaking the turfgrass swards into smaller areas and consistently sampling the same area(s) can provide more accurate assessments of nematode populations.

Credit: John Kaminski/Penn State University

Management

Management options for nematodes is limited. Generally, it is recommended to maintain a healthy turfgrass stand and select  nematicides that can effectively target the genera present at your location.

Cultural

No turfgrass cultivars are resistant to feeding by all nematode species. However, cultural practices that promote vigorous root growth can help suppress visual symptoms of nematode damage. Fertilization, the application of wetting agents, and the use of organic materials such as humates can assist in limiting nematode damage and reducing stress on turf plants. It is important to consult local extension specialists for current nematode management strategies specific to the nematode species and climatic region.

Chemical

Chemical fumigants or nematicides may be recommended when nematode counts exceed established thresholds and when turf shows symptoms consistent with nematode damage. However, the use of nematicides should be based on nematode assays and periodic sampling, as the efficacy of nematicide programs may not always result in a decline in nematode populations.

Fumigants are typically used before seeding due to their high toxicity to plants. Certain synthetic organic nematicides, such as abamectin, fluopyram, and furfural, are registered for use on turf, but their selection should be based on previous nematode sampling.

Timing of nematicide applications often coincides with turfgrass root growth, but it can vary in different climatic zones. Proper post-application irrigation is essential for the effectiveness of nematicides. It is important to note that there is limited data supporting the efficacy of biological materials for nematode management in turfgrass systems.

Nematicides and fumigants can be toxic to animals and should be used and handled strictly according to the instructions provided on their labels.