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Key Takeaways

  • Not all nematodes found in the soil are detrimental. Some feed on soil pests, mineralize nutrients and decompose organic matter.
  • If you think nematodes are responsible for turf damage, proper sampling is essential to determine the species present and the population sizes.
  • Tolerance thresholds for plant-parasitic nematodes can vary greatly depending on the species of nematode, turf species and variety, soil type and condition, location and climate.
  • Cultural practices – particularly adequate irrigation and fertilization – may allow you to manage nematode issues under light-to-moderate pressure without the need for chemical applications.
  • Test control products on a small scale first to determine their effectiveness so you avoid wasting time and money on larger applications that may not work.
     

Nematodes are ubiquitous in soil and are a concern for turfgrass managers in many parts of the U.S., but not all nematodes are problematic on golf courses (Cobb, 1915). Some can be beneficial to turfgrass growth and around half of nematode species are not parasitic to plants. Nematodes that feed on algae, bacteria, fungi, protozoa and other nematodes, or parasitize insects and animals may help to control potential turfgrass pests. Nematodes can also help to mineralize nutrients and decompose organic matter. Golf course superintendents should keep these facts in mind as they plan control strategies for nematodes they believe are responsible for turfgrass issues.

Plant-parasitic nematodes typically range in size from 0.5-4.0 mm in length and are thinner than a human hair. They can move in a thin film of water, have a protractible spear-like structure called a stylet, and need a live host plant to survive and complete their life cycle. They feed on plants by penetrating their stylet into living cells, injecting digestive juices and feeding on their contents. Ectoparasitic nematodes live in soil and puncture the endodermis and cortex of roots to feed. Endoparasitic nematodes that live within roots can burrow through cells to reach new feeding grounds (migratory), or set up shop in a group of cells and live their life in one spot (sedentary). These distinctions have implications for control, so it’s important to know which kind of nematodes are causing issues.

Symptoms of nematode damage can vary, and damage caused by other pests or cultural issues can often be mistakenly diagnosed as nematode-related. In general, turfgrass experiencing nematode damage will have roots that are shorter and darker than normal. The roots typically lack fine feeder roots, and their ability to utilize nutrients and water is compromised. Cellular damage also diminishes the plant’s ability to defend against soil-borne pathogens. Infested turf areas can become thin, weedy, necrotic and may ultimately see widespread turf loss.

Dead and dying turf creates poor playing conditions, particularly on golf course greens where consistent ball roll is very important. Some areas may need to be regrassed when damage becomes too severe. Unfortunately, it can take weeks after planting to restore a smooth putting surface and nematodes can reinfest these areas, causing another round of decline. The first step in successfully managing nematode issues is knowing the species that caused the damage so you can choose the right control strategy.

Soil sampling methods

Proper sampling is necessary to determine if plant-parasitic nematodes are present in sufficient numbers to cause damage. During the winter, when roots have become inactive, most nematodes are overwintering as eggs and will not be counted in nematode assays. Dead grass will also not contain a lot of live nematodes and should be avoided when sampling. To determine if nematodes are a problem, cores should be taken from a stressed area when turf is actively growing. Another aggregate sample can be collected from an area that is not showing symptoms for comparison.

A single cup-cutter sample may give misleading results. It is better to collect 10-20 smaller samples – approximately 1 inch in diameter – to the depth of the roots and combine them together in a sealed plastic bag to retain moisture (Butler & Kerns, 2020). Hand deliver or ship the samples overnight to a nematode testing lab early in the week so they can process them before the weekend. Consider using a cold pack to keep nematodes cool enough to survive the process. It is also important to check with your testing lab to see if they have other requirements or recommendations for sampling.

Threshold levels

Tolerance thresholds have been developed to determine when populations of different nematode species become problematic. Thresholds are not carved in stone; they are estimates and do not always consider other nematodes that might be present, turfgrass cultivar, height of cut, soil compaction, root depth and health, fertilization, time of year, growing zone or disease pressure (Mitkowski, 2017). Some thresholds are developed in greenhouses by inoculating sterilized soil with a specific nematode to take other nematodes and stressors out of the equation.

If you send in soil samples because your turfgrass is declining and some nematode species are near or over established local thresholds, it may dictate some action. If you are just submitting seasonal samples for tracking purposes and have not had any issues with turfgrass quality, those same numbers may not be a real cause for concern. When in doubt, apply treatments – e.g., fertilizer, fungicides or nematicides – individually to small, straight-edged areas. This way you can determine if a product produced a positive result, as biotic issues rarely produce straight edges. If you decide to treat on a larger scale, try to leave some untreated areas for comparison.

An initial small-scale treatment approach is beneficial if you think nematodes are responsible for turf damage at your course because it:

  • Helps you confirm whether nematodes are actually causing the issue.
  • Allows you to test whether control products are effective.
  • Prevents you from applying large amounts of ineffective products.
  • Can save money and time, and minimize unwanted impacts.
  • Allows you to dial-in treatment rates before making larger applications.

 

Cultural management

Limiting nematode damage does not necessarily require chemical control. Cultural practices can play an important and effective role. Starting out by planting into sterilized soil and using “nematode-free” sprigs or sod gives you the best chance for success since effective nematicides are very limited and some species are very difficult to control. Testing plant material prior to delivery can help reduce the influx of nematodes. Planting nematode-resistant cultivars is also a good idea in areas prone to severe nematode damage. For example, ‘TifDwarf’ and ‘Emerald Dwarf’ are known to tolerate sting nematodes better than the ultradwarfs (Crow, 2020).

Proper irrigation may be the most effective way to manage light-to-moderate nematode infestations. Damage caused by nematodes directly impacts the ability of turfgrass to utilize water and nutrients, and wilting is normally the first symptom to develop as root systems become compromised. Regular syringing during hot days can sometimes be enough to manage marginal nematode levels.

Proper fertilization is also very important. Too much nitrogen can cause succulent growth and allow nematode numbers to rise excessively, while too little nitrogen will not be sufficient to feed the turf when its root system is compromised. Light and frequent nitrogen applications can help improve turf quality even though nematode numbers may rise due to increased rooting (Butler & Kerns, 2020). Foliar fertilization is more efficient when applying micronutrients – particularly when roots are compromised and soil pH is high – and can complement soil applications of nitrogen, phosphorous and potassium. Organic nitrogen derived from sewage – e.g., Milorganite – was found to reduce sting nematodes and increase root and leaf growth (Heald & Burton, 1968).

Mechanical practices like aerification and verticutting create a healthy environment for turf growth by reducing soil compaction and thatch concentration. Unfortunately, these practices, along with topdressing, can enhance nematode stress symptoms shortly after they are performed. Adding soil amendments that have either clay-containing colloidal phosphates or organic matter – e.g., Comand compost – increases nutrient- and water-holding capacity, which helps turfgrass tolerate nematodes (Crow, 2020). Raising mowing height also helps increase tolerance, and even a slight increase on golf greens can make a visible difference. Overseeding can increase nematode numbers and transition problems if not managed properly (Crow et al., 2005).

Chemical control

Nematicides may be needed when cultural practices are not enough to adequately manage nematode stress. Chemical nematicides for use in turf are currently limited and effective biological products are even scarcer. Any product claiming to be a nematicide requires an EPA registration number and approved label. To get these the seller needs to conduct experiments that show sufficient efficacy. Products only claiming plant health benefits are not subject to this scrutiny. If products without EPA registration are considered, it is best to apply them on a small scale at first to determine if larger-scale applications are warranted.

Chemical control of nematode populations is generally best done early in the year when numbers are lower, some endoparasitic nematodes are outside of roots, juveniles are more abundant, and sting nematodes are closer to the surface. Bionematicides, such as Zelto, will also typically have the greatest impact at this time (Crow, 2020). Nematode control programs often start with biologicals around the time of egg hatching and chemical nematicides are applied afterward if conditions warrant.

Current chemical nematicides basically contain one of these active ingredients: 1,3-dichloropropene, abamectin or fluopyram, and they all belong to different chemical classes (Crow, 2020). Check labels for efficacy on specific nematode species and rotate products to prevent resistance.

A sound fungicide program can complement nematode control programs by reducing the chance for soil-borne diseases to enter damaged roots and infect turfgrass. Fungicides that are effective on pythium and take-all root rot are particularly beneficial. Iprodione and thiophanate-methyl have low levels of nematicidal activity and can be inserted into disease-control programs at a timing similar to biological products. Be cautious using SDHI fungicides if nematodes are an issue since fluopyram is also in Group 7 and nematode resistance may become an issue.

Plant-parasitic nematodes and their control

The following is a list of the primary plant-parasitic nematodes that are a concern to golf course turf managers along with recommendations for control. Control products and strategies differ considerably depending on the nematode species, so proper sampling and identification is a critical first step in successful management.

Sting

Nematodes referred to as “sting” in the United States are typically Belonolaimus longicaudatus and are considered the most damaging to turfgrass. They are native to the sandy coastal plains of the Southeast but are currently also found in areas like Kansas, Ohio, New Jersey and Southern California in soils containing at least 80% sand and less than 10% clay.

Pasteuria bacteria are natural enemies of sting and root-knot nematodes and can affect populations (Young & DiGennaro, 2018; Giblin-Davis, 1990). Zelto (Burkholderia spp. strain A396) is currently labeled for sting nematode control and is most effective when nematode pressure is low (Crow, 2020). Indemnify (fluopyram) is usually highly effective against sting nematodes and can provide several months of control. Curfew (1,3-dichloropropene) is highly effective against sting and other ectoparasitic nematodes. Abamectin has a high affinity for organic matter and tends to stay in the thatch, so applications made in cooler months give you the best chance for control of sting nematodes since that is when they are closer to the surface (Crow, 2017).

Lance

These semi-endoparasitic nematodes tunnel in and out of roots and are major pests of both warm- and cool-season turf. Hoplolaimus galeatus can be found in the northern U.S. and is the most common species found in Florida (Crow, 2020; Mitkowski, 2017). When inside roots, lance nematodes and their eggs are protected from contact nematicides. Lance nematodes are most exposed just before spring greenup when bermudagrass starts to produce new roots (Crow, 2017).

Zelto, Curfew and abamectin-based products have some level of efficacy on Hoplolaimus galeatus outside of roots, while Indemnify is not effective. The most recent systemic nematicide with efficacy against lance nematodes was Nimitz (fluensulfone) but it is not currently for sale. Repeat applications of abamectin and fluopyram are associated with increases in lance nematodes, which is most likely due to reduced competition from other nematode species (Crow, 2021).

Root-Knot

Considered to be the most important plant-parasitic nematodes in the world because of their impact on crop production, Meloidogyne spp. are major pests in crops and turfgrass. In turfgrass, they are in the top three for concern along with sting and lance. They are initially slender and motile but grow fatter as they mature. Females migrate until they find a feeding spot within a group of root cells, creating swollen roots, and then they become sedentary. Roots typically die off below infection sites and do not go much deeper than the thatch layer since that is the area typically infected. Dr. Billy Crow from the University of Florida developed a mist-extraction method for identifying these nematodes in turfgrass, but it requires a slightly different sampling method (Crow, 2020).

Abamectin-based products are effective when repeatedly applied during the summer. Indemnify is also effective and the best results are obtained with at least two applications. Curfew only provides control when contact occurs outside of the roots.

Cyst

The endoparasitic cyst nematode (Heterodera spp.) is similar to root-knot nematodes and creates galls when they settle in root cells. Thresholds and control are also similar for cyst and root-knot nematodes.

Spiral

This is one of the most commonly found nematodes on plants, particularly since numerous species are classified as spiral nematodes. The main criterium is that they curl into a spiral when relaxed or dead. Spiral nematodes found in the northern U.S. typically only cause droughty symptoms. However, Helicotylenchus pseudorobustus ‘Type E’ can cause major damage to ‘TifDwarf’ bermudagrass and seashore paspalum.

Indemnify does not control most spiral nematodes but has good efficacy on Helicotylenchus. Curfew is also effective, and abamectin is labeled for control of spiral nematodes.

Stubby-Root

Found in most states, and named for the damage they cause to turfgrass roots, stubby-root nematodes (Nanidorus spp.) are the only plant-parasitic nematodes with a solid, curved stylet. Current nematicides do not appear to be as effective as older chemistries, and populations have been known to rebound after fumigant applications since they are often found deep in the soil (Crow, 2014).

Ring

Although damage from ring nematodes (Criconemella spp.) is relatively rare, they are often found in damaged areas with spiral, stubby-root and stunt nematodes in the Midwest, and with stunt, spiral and lance nematodes in the Northeast (Walker, 2002; Wick, 2012). Distinct rings around their body is what gives them their name. Mesocriconema ornatum moves upward in the soil profile during the summer making them more available for control (Crow, 2017). All products in Table 1 are labeled for control of ring nematodes but the level of control may vary depending on the species present and their depth in the soil.

Stunt

Ectoparasitic stunt nematodes (Tylenchorhynchus spp.) are mostly a problem when turf is under stress, but significant damage can occur when found with lance nematodes in northeastern putting greens (Wick, 2012). If needed, Curfew and Indemnify are the most effective products for control of stunt nematodes.

Needle

Only 30 ectoparasitic needle nematodes (Longidorus spp.) per 100 cubic centimeters of soil can prevent turfgrass seed from establishing (Wick, 2012). Sometimes found in finer native soil, needle nematodes can cause significant damage alone or when found with ring and lesion nematodes (Warner, 2013). Curfew and Indemnify are the most effective products for control of needle nematodes.

Stem-Gall

Anguina pacificae are found on Poa annua greens near the coast of California from the Monterey Peninsula to San Francisco on some very high-profile golf courses. Stem-gall nematodes are found at the base of the turf crown and symptoms usually become noticeable around midsummer. Damage from these nematodes can create pits in the putting surface that greatly affect ball roll. Golf course managers were dependent on products containing azadirachtin after the loss of Nemacure, but are now able to use abamectin and fluopyram in their control programs.

Summary

Correct sampling and identification of nematode populations helps determine the best management practices. Use thresholds mostly as a guide and determine the best course of action by evaluating the entire situation. Sometimes reducing stressors can be enough to manage nematode infestations. If not, small-scale treatments can confirm whether nematodes are causing an issue and which products are effective. If treatment with nematicides becomes necessary, try to rotate products to avoid developing resistance.           

References

Butler, L., Kerns, J., & Galle, G. (2020). Nematodes in turf. North Carolina State Extension Publications. 

Cobb, N.A. (1915). Nematodes and their relationships. (1914 Yearbook of the Department of Agriculture). U.S. Government Printing Office.

Crow, W.T. (2014). Stubby-root nematode. UF-IFAS (EENY-339). University of Florida.

Crow, W.T. (2015). Lance nematode. UF-IFAS (EENY-234). University of Florida.

Crow, W.T. (2020). Nematode management for golf courses in Florida. UF-IFAS (EENY-008). University of Florida.

Crow, W.T. (2021). Managing lance nematodes in warm-season turfgrass. Golf Course Management, 89(10), 60-64.  

Crow, W.T., Lowe, T., & Lickfeldt, D. (2005). Overseeding and nematicides affect sting nematodes in bermudagrass fairways. USGA Green Section Record, 43(6), 8-11.

Crow, W.T., Becker, J. O., & Baird, J. (2017). New golf course nematicides. Golf Course Management, 85(7), 66-71.  

Dyrdahl-Young, R. & DiGennaro, P. (2018). Pasteuria penetrans (Bacilli: Bacillales: Pasteuriaceae). UF-IFAS (EENY-718). University of Florida.

Giblin-Davis, R.M. (1990). Potential for biological control of phytoparasitic nematodes in bermudagrass turf with isolates of the Pasteuria penetrans group. Proceedings of the 103rd Annual Meeting of the Florida State Horticultural Society, (pp. 349-351). University of Florida Press.

Heald, C.M., & Burton, G.W., (1968). Effect of organic and inorganic nitrogen on nematode populations in turf. Plant Disease Reporter, 52(1), 46-48.

Mitkowski, N.A., (2017). Nematodes on northern turfgrasses. Golfdom, 73(7), 32-35.  

Walker, N.R., Goad, C.L, Zhang, H., & Martin, D.L. (2002). Factors associated with populations of plant-parasitic nematodes in bentgrass putting greens in Oklahoma. Plant Disease, (86)7, 764-768. http://dx.doi.org/10.1094/PDIS.2002.86.7.764

Warner, F. (2013). Importance of nematodes on turfgrass and landscape plants.  National Plant Diagnostic Network National Meeting, Washington, DC. 

Wick, R. (2012). Nematodes on golf greens. UMass Extension Turf Program.