• Topics: Entomology and Nematology  | Athletic Fields  | Non-residential Lawns  | Commercial Turf Pest Nematodes  | Commercial Turf, Nursery, and Ornamentals  | Crow, William T 

Nematode Management for Non-Residential Lawns, Athletic Fields, Racetracks, and Cemeteries in Florida¹

Turfgrasses help beautify our environment, reduce water runoff and reduce water and air pollution. They are also essential components of many athletic fields, racetracks, and cemeteries. Just like any other crop, pest management is a key for growing healthy grass. Plant-parasitic nematodes are probably the least understood and most difficult to manage of the turfgrass pests in Florida (Figure 1).

Figure 1. 

Diagram of a typical plant-parasitic nematode.

What Are Nematodes?

Nematodes are unsegmented roundworms, different from earthworms and other familiar worms that are segmented (annelids) or in some cases flattened and slimy (flatworms). Nematodes living in soil are very small and most can only be seen using a microscope (Figure 2). There are many kinds of nematodes found in the soil under any turf. Most of these are beneficial, feeding on bacteria, fungi, or other microscopic organisms. There are even nematodes that can be used as biological control organisms to help manage important turf insect pests. Unfortunately, there are also a group of nematodes that feed on plants, these are called plant-parasitic nematodes (Figure 1).

Figure 2. 

Size comparison of a typical plant-parasitic nematode to a cotton thread.

All plant-parasitic nematodes have a stylet or mouth-spear that is similar in structure and function to a hypodermic needle (Figure 3). The nematode uses the stylet to puncture plant cells, and then inject digestive juices and ingest plant fluids through it. All of the plant-parasitic nematodes that are important turfgrass pests feed on roots. Some plant-parasitic nematodes remain in the soil and feed by inserting only their stylet into the root, these are called ectoparasitic nematodes (Figure 4). Others, using their stylet to puncture an entry hole in the root, feed with their body inside the root tissue. These are called endoparasitic nematodes (Figure 5). Of the major nematodes that cause damage to turfgrasses in Florida, sting, awl, stubby-root, sheath, sheathoid, and ring nematodes are strictly ectoparasites, root-knot nematodes are strictly endoparasites, and lance nematodes feed both endo and ectoparasitically.

Figure 3. 

A typical plant-parasitic nematode stylet resembles a hypodermic needle.

Figure 4. 

An ectoparasitic nematode feeding by inserting its stylet into a root tip.

Figure 5. 

Endoparastic nematodes burrowing within a root.

How Do Nematodes Affect Turf?

As plant-parasitic nematodes feed they damage the root system and reduce the ability of the grass to obtain water and nutrients from the soil. Roots may be abnormally short and appear darkened or rotten when damaged by plant-parasitic nematodes (Figure 6). Often the roots will appear “cropped off” an inch or so below the soil surface (Figure 7). Root galls or knots associated with certain nematode damage to other crops are usually not evident on grasses.

Figure 6. 

Healthy grass roots (left) and dark, rotting grass roots damaged by nematodes.

Figure 7. 

Healthy bermudagrass roots (right) and roots that have been cropped off at about 1/2 inch deep by nematodes (left).

When nematode population densities get high, and/or when environmental stresses such as high temperatures or prolonged low light occur, aboveground symptoms may become evident. Symptoms include yellowing, wilting, browning, or thinning out. Grass will die under extreme nematode and environmental stress. Often, as the grass thins out weeds, particularly spurge (Figure 8), sedge, (Figure 9) or Florida pusley (Figure 10) may become prominent. Nematode damage usually occurs in irregularly shaped patches that may enlarge slowly over time (Figure 11). Be aware that similar conditions may be caused by other factors such as localized soil conditions, fungal diseases, or insects.

Figure 8. 

Spurge, a weed often associated with turf, declining from nematode injury.

Figure 9. 

Sedge, a weed often associated with turf, declining from nematode injury.

Figure 10. 

Florida pusley, a weed often associated with turf, declining from nematode injury.

Figure 11. 

Typical nematode symptoms on a lawn; irregular patches of declining grass.

Sting nematodes are the most damaging of the plant-parasitic nematodes and can damage all types of turf grasses, even occasionally Bahiagrass. Lance nematodes can damage all types of turf but are the most common nematode causing damage to St. Augustine. Ring nematodes are common problems on centipede, but only rarely do they damage other grasses. Other common nematodes that occasionally damage turf in Florida are stubby-root nematodes, root-knot nematodes, awl nematodes, sheath nematodes, and sheathoid nematodes. Nematodes that are common but rarely damage turf in Florida are lesion, stunt, and spiral nematodes.

How Do I Know If Nematodes Are A Problem?

With any plant problem, having an accurate diagnosis is important to address the problem and to avoid wasting effort and unnecessary pesticide applications. The only reliable way to determine if plant-parasitic nematodes are involved in a grass problem is by having a nematode assay conducted by a professional nematode diagnostic lab. The Florida Nematode Assay Lab is such a facility and will assay nematode samples for a cost that is currently $20 for each sample from Florida and $25 for each sample from outside of Florida. Nematode sample kits (Figure 12) containing everything needed to collect and submit a sample, along with instructions, are available at your local county Cooperative Extension office.

Figure 12. 

The University of Florida Nematode Sample Kit.

Nematode analysis is a separate procedure and requires different sampling guidelines than those required for soil analysis or plant disease samples. Be aware that when a plant disease sample is submitted to most labs a nematode analysis is not normally performed unless you specifically request it. Nematode analysis often requires separate payment and may even be sent to a separate address. Familiarize yourself with the procedures required by the lab where you intend to submit the sample. The accuracy of the diagnosis depends on the quality of the sample that you submit. If you are taking a sample for submission to another lab, or if you are submitting a sample to the University of Florida lab without using our sample kits, following the guidelines below will help insure an accurate diagnosis:

1) A sample must consist of multiple soil cores. Nematodes are not evenly distributed in soil, but rather congregate in “hot spots.” Nematode populations may be high at one spot and low just a few feet way. By collecting multiple cores with a device such as a “T” type soil sample tube (Figure 13) an average population density can be measured. A good rule of thumb is to have a minimum of 20 cores per field. Cores should be taken to a depth of 3 inches.

Figure 13. 

A "T" type soil sample tube is ideal for collecting nematode samples from turf.

2) If damage is evident then sample near the margin of the affected area (Figure 14). Nematode populations will decline in severely damaged areas because they have nothing left to eat. Therefore, populations tend to be highest near the edges of a declining area where the grass is still alive. If damage is occurring in a number of areas in one field take a few cores from the border of several affected areas to make the 20 cores.

Figure 14. 

Collect cores for a nematode sample from the edges of declining areas.

When taking samples from turf that is not showing symptoms, or if sampling before planting, sample in a “zig-zag” pattern across the area (Figure 15).

Figure 15. 

When sampling healthy appearing turf, collect cores in a zig-zag pattern across the area.

3) Put the soil from each sampled area into a plastic bag and seal it. Nematodes require moisture to survive so drying the soil will kill them. This is different than submitting a sample for nutrient analysis where dry soil is preferred. Make sure that each bag is labeled with a permanent marker so that the diagnosis can be assigned to the correct area. If using a self-sealing bag seal it with tape also because the zippers often come open in transit.

4) Handle samples carefully. Do not expose samples to direct sunlight or heat. Nematodes are sensitive to high temperatures and UV light. Leaving samples on the dashboard or in the back of a pickup truck can kill them quickly and negatively affect the accuracy of the diagnosis. Keeping the nematode sample in a cooler is best.

The nematodes will be sandwiched between soil particles so rough handling will destroy them. For shipping and transport pack the samples well to minimized shifting.

5) Submit the sample right away. Next day delivery is best. One study found greatest nematode recovery from hand-delivered samples, the next highest from next-day delivery, and the lowest from regular postal delivery.

The staff at the University of Florida Nematode Assay Lab will make a determination on whether or not nematodes are a problem based on which nematodes are found and how many of them there are. Not all plant-parasitic nematodes are equal in their ability to harm grass. For example, one sting nematode can cause damage equal to hundreds of individuals of some other types of plant-parasitic nematodes. The number of each type of nematode in 100 cc of soil from the sample that you submit will be used to determine the risk level for the turf species indicated (Table 1). The risk level will tell you if the turf is at low, moderate, or high risk of damage from plant-parasitic nematodes.

Be aware that different diagnostic labs may use different extraction techniques, use different quantities of soil, or use different thresholds. Because of this, samples submitted to separate labs may report different quantities of nematodes. Do not be alarmed by this, in most cases the different thresholds used are adjusted to account for the differences in methodology and local conditions. However, if you are using a lab in distant locations, your local conditions or regional variations in nematode aggressiveness may not be taken into account. Often your local labs will provide the most accurate assessments.

How Do I Manage Nematodes?

Before Planting

It is always preferable to avoid a potential problem than to deal with an existing one, so it is best to consider nematodes before planting or replanting. The first consideration, especially for an area that has had nematode problems in the past, is grass selection. Not all nematodes are equally damaging on all grasses. Generally bahiagrass is the most tolerant of all turfgrasses to nematodes and is a good choice for chronically affected areas. Usually centipedegrass is the most susceptible to damage from ring nematodes and should be avoided when these nematodes are prevalent. Cyst nematodes are only a problem on St. Augustinegrass.

Chemical management of nematodes before planting can be performed using the fumigant Dazomet. This product is sold under the tradename Basamid®. Dazomet is a granular material that releases gasses that are toxic to nematodes after it is incorporated with soil. This can be helpful in getting the grass to establish in nematode infested soils. However, Dazomet will not kill all of the nematodes, and they may build back up to damaging levels over time. Dazomet is a toxic poison, therefore only professional pesticide applicators with a special license may apply it. The product label must be strictly adhered to insure safety to the applicator and nonorganisms (plants, animals, children).

Contaminated planting material (sod or sprigs) are a means whereby nematodes can be spread into new areas. It may be worthwhile to have potential sod tested for the presence of large numbers of the more damaging turf nematodes (sting and lance nematodes) before purchase.

Established Turf

Cultural Practices

Turf can often exist with a given population density of plant-parasitic nematodes with no visible damage. Damage usually becomes evident when one of two things occur; 1) some other factor increases the susceptibility of the grass to nematode damage and/or 2) some factor causes nematode population densities to increase to damaging levels. Once the grass is planted, the best way to reduce the likelihood of nematode damage is to minimize these factors as much as possible.

Mowing:

Generally speaking the lower the grass is mowed the greater the stress the grass is under. Often raising mowing height slightly can reduce nematode damage considerably. Infrequent mowing should be avoided. The more foliage is removed at each mowing, the greater the stress that is put on the grass.

Fertility:

Excessive nitrogen fertilization can increase succulent root growth and encourage rapid foliage growth. Succulent root tips are more susceptible to nematode damage, and the proliferation of root tips (nematode food) can cause nematode population densities to rise dramatically. Rapidly growing foliage drains nutrient reserves from the roots that are needed to compensate for the nematode damage.

Under-fertilization should also be avoided. Roots damaged by nematodes will already have a reduced capability to extract nutrients from soil. This makes nutrient deficiencies more pronounced on nematode-infested plants.

Watering:

Deep, infrequent watering encourages deep root growth. A deep root system is more tolerant of nematodes than a shallow root system resulting from shallow, frequent watering. However, once nematode damage is extensive, frequent watering may be required to keep the grass from wilting. In this case water should be applied only often enough to avoid wilting and only enough to allow water penetration as deep as the root system.

Compaction and aeration:

Over-compaction reduces oxygen penetration to the root system and enhances susceptibility to nematode damage. Aeration encourages a healthy root system and thereby enhances tolerance to nematodes.

Soil amendments:

Generally anything that promotes healthy root growth can enhance tolerance to nematodes. Incorporation of colloidal phosphate has been shown to enhance bermudagrass tolerance to several nematodes. Some organic amendments such as composted municipal sludge or composted manures may also reduce nematode damage and speed the recovery process after damage has occurred.

Chemicals

Even the best managed turf can suffer from nematode injury. In order to kill nematodes in soil, nematicides are toxic at low levels and are water soluble in order to move down to where the nematodes are. Many of the effective nematicides used in the past have been withdrawn from the market during the last 25 years for environmental and health reasons until only a handful remain. There are no nematicides labeled for use on racetracks or athletic fields in Florida. Fenamiphos is the active ingredient in Nemacur® 10%, this product is labeled for use on cemeteries, golf courses, and industrial grounds. Other formulations of Nemacur® cannot be used on cemeteries or industrial grounds. Nemacur is currently under a phase-out and will no longer be produced as of May 2007. However, sales of existing stock may continue through May 2008. Additionally, Nemacur can no longer be used on certain areas defined on the label which states "After May 31, 2005, do not apply to hydrologic soil group A soils that are excessively drained and predominately sand or loamy sand such as soils in the suborder psamments with shallow water tables (less than 50 feet deep). These classifications and soil taxonomy refer to USDA definitions. If you are unsure of the type of soil you are treating, please consult with your county's extension agent or the product manufacturer." See the Bayer Procentral website for more information regarding the phase-out of Nemacur.

Curfew Soil Fumigant has 24(c) labeling and can be used for nematode control on athletic fields and racetracks in Florida and is a very effective nematicide. Curfew Soil fumigant can be applied only by an approved commercial applicator using specialized application equipment. The fumigant is injected as a liquid 5 to 6 inches deep in the soil using tractor-mounted slit-injection equipment (Figure 16). After injection, the active ingredient moves through the soil as a gas and kills nematodes upon contact. Curfew Soil Fumigant now has 24(c) labeling for use on golf course and athletic field turf in Florida, Georgia, South Carolina, North Carolina, Alabama, and Mississippi. According to the product label, Curfew cannot be used on areas with Karst geology (including much of Miami-Dade County). Curfew has a 24 hour reentry restriction as well as a 100 ft. buffer zone to buildings and wells.

Figure 16. 

Equipment used for applying Curfew Soil Fumigant to turf.

Because of the lack of nematicides labeled for use on athletic fields, racetracks and cemeteries, a great deal of emphasis is being placed on finding less-toxic nematode control products. Many of these are “biological derivatives" of plants or microorganisms or “biological control" products. Others are non-biological, but are marketed as “non-toxic" or "organic." These types of products often are safe, but do not need to be proven to be effective to be labeled.

Faculty at the University of Florida are committed to testing as many of these products for efficacy as possible. Additionally, we network with researchers at other institutions to gather their experience working with these products. While we have data on many of these products, we do not have data on all of them. Feel free to contact us for information on our experience with specific products.

Summary

Nematode management can be a daunting task. Expectations for pristine turf are high and nematodes are notoriously difficult to control. The best management practices for turfgrass with nematode problems are: 1) avoid other stresses on the grass as much as possible, 2) monitor nematode populations by sampling frequently, 3) apply chemicals only when needed.

The University of Florida is committed to bringing you the most current information possible. Consequently this document will be modified with each breaking development. The most current version of this document may be obtained at your county Cooperative Extension office, or found on line at the University of Florida's Electronic Document Information System (EDIS) website at http://edis.ifas.ufl.edu/.

For additional information regarding nematodes, nematode management, or help interpreting nematode assay results contact:

Dr. W. T. (Billy) Crow, Landscape Nematologist, Entomology and Nematology Dept., PO Box 110620, Gainesville, FL 32611, (352) 392-1901 ext. 138, FAX (352) 392-0190, Email: wtcr@ufl.edu

For information on submitting samples to the University of Florida Nematode Assay Lab or to check on the status of a sample you submitted contact:

Mr. Frank Woods, Senior Biologist, Nematode Assay Lab, PO Box 110820, Gainesville, FL 32611, (352) 392-1994, FAX (352) 392-3438, Email: nemalab@ifas.ufl.edu

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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