Soil Salinity and its Effects on Turfgrass Pests

Management of soil salinity and pests are among the most critical components of maintaining a healthy stand of turfgrass.^1,2 Salinity and pest management are increasingly severe issues for turfgrass managers. Individually, soil salinity and pests cause a great deal of damage to most turfgrass species; in combination, their impacts on turfgrass health are highly situational.^3,4 This article aims to introduce and inform turfgrass management professionals, extension agents, and research institutions about an unconventional relationship between soil salinity and turfgrass pest management.

Introduction

High disease pressure and poor-quality irrigation water are both significant factors affecting turfgrass growth and quality in the southeast region. Climatic conditions in the southeast are highly variable and, therefore, conducive to the growth of many turfgrass microbial pathogens.⁵ Furthermore, across the United States, high-quality irrigation sources are becoming scarce and more expensive for turfgrass managers, forcing use of lower-quality, non-potable or recycled wastewater for irrigation.⁶ One issue associated with use of poor-quality water is the potential for development of saline soils that impair turfgrass quality and health.

Increasing reliance on poor irrigation water quality has caused many turfgrass managers to alter their management practices to obtain desired turfgrass performance and soil health. Salinity also affects a wide array of abiotic and biotic factors beyond turfgrass growth and development.^1,3,4,7-9 Therefore, proper water and disease management are critical to effectively maintain turfgrass landscapes such as golf courses and athletic fields at the highest quality. Both issues of increased disease pressure and the use of saline irrigation water pose threats to turfgrass health. An abundance of research and information has been published on how saline irrigation and various pathogens impact turfgrass growth and development individually; however, limited research has been published on how the two factors interact with each other to affect turfgrass quality and performance.

Soil Salinity and the Environment

Saline soils are soils that contain high concentrations of soluble salts that can be detrimental to plant growth and are capable of imposing salinity stress on plants. These soluble salts contain cations such as sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) along with anions chloride (Cl^–), sulfate (SO₄ ^2-), nitrate (NO₃ ^–), bicarbonate (HCO₃ ^–) and carbonate (CO₃ ^2-).¹⁰ Soil salinity is caused by a variety of natural processes, including rock weathering and fluctuating depth of the water table. Weathering dissolves soluble salts from rocks, enabling solutes to move with water through the soil solution. The fluctuating depth of the water table determines where the soluble salts will be in relation to the root zone, directly impacting both plant growth and soil structure. Alongside the fluctuating depth of the water table, saltwater intrusion is a common cause of soil salinity in coastal regions.¹⁰ The most common anthropogenic causes of soil salinity include the use of salt-forming chemical inputs such as fertilizers, soil amendments, and pesticides.¹¹ Soil salinity can impose a variety of issues on both turfgrass and soil health. Cellular water loss, reduced water uptake, and disruption of ion balances leading to ion toxicity are the most common issues associated with turfgrass salinity stress.¹¹ While both soil chemical and physical properties can be negatively affected by excess salinity. Excess salts in soil solution may increase the soil electrical conductivity (EC) and sodium absorption ratio (SAR). Both of which are used to predict whether sodium-induced dispersion will more greatly affect certain soil physical properties such as infiltration, hydraulic conductivity, and surface crusting. Decreased water infiltration, decreased hydraulic conductivity (the ability of the soil to transmit water), and increased surface crusting are common effects that soil salinity has on soil health that may result in decreased plant productivity due to poor aeration and reduced water supply.

On the other hand, sodic soils are soils that have greater than 15 percent sodium ions (Na⁺) attached to their cation exchange sites and have a pH of 8.5 – 10.¹⁰ In contrast to saline soils, sodic soils do not have high concentrations of the other soluble salts. The high pH and amounts of Na⁺ in sodic soils are due to the hydrolysis of sodium carbonate (Na₂CO₃). High pH paired with the presence of CO₃^2- causes other cations, such as Mg²⁺ and Ca²⁺, to precipitate.¹⁷ Therefore, sodic soils tend to have poor soil structure and unfavorable physical properties such as poor water infiltration and air exchange that can reduce plant growth.¹⁰

Figure 1. Clay soils can either be flocculated if adequate Ca and Mg are present in the soil (left) or dispersed if too much sodium is present (right). This influences water movement through the soil column. Image credit: Dr. Dara Park and Dr. Sarah White, Clemson University.

The use of saline irrigation water and recycled wastewater has been widely studied for its effects on soil properties and turfgrass growth. Higher sodium content in irrigation water results in a higher pH and more alkaline soil conditions. Extractable Na⁺ from soils increased 200% or more when turfgrasses were irrigated with recycled wastewater.¹ An accumulation of large sodium ions disrupts the forces that bind the clay particles together, resulting in shrinking, swelling, and soil dispersion (figure 1).⁸ When the sodium induced dispersion occurs and the soil is repeatedly wetted and dried, it reforms and solidifies to plug soil pores and reduce soil permeability. Decreases in soil permeability create adverse effects on certain soil physical properties such as water infiltration, aeration, and root penetration/growth that may hinder plant productivity.⁸

High soil salinity is also associated with reduced turfgrass shoot growth due to salt accumulation in the rhizosphere, hindering the roots’ ability to withdraw water from the surrounding soil.¹¹ Salinity levels greater than 3.2 dS/m caused a 25% reduction in shoot growth in salt-sensitive cultivars of Kentucky bluegrass in fine-textured soils.¹ The same study indicated turfgrass recovery from traffic, biotic, and other abiotic stressors decreased as soil salinity increased. Along with the reduced quality of mature turfgrass, high soil salinity is known to lower seedling emergence rates during overseeding practices, as cotyledons are highly sensitive to salt during emergence.⁷

In addition, many environmental and soil physical and chemical properties affect how a particular soil type accumulates salts and the relative susceptibility of turfgrass species to salinity stress. Environmental factors affecting salinity tolerance include temperature, water status, light, soil depth, soil particle fineness, timing, and depth of irrigation. Hot, dry conditions make turfgrasses more sensitive to saline conditions as increased evapotranspiration rates favor salt uptake. Salt accumulation occurs more rapidly in soils with thick thatch layers. Clay-dominant soils can have low permeability and become compacted when clay particles become dispersed when too much Na is present, in contrast with calcium and magnesium, ions that help aggregate the soil (figure 1). Therefore, soils that have a clay-dominant texture tend to accumulate soluble salts and hinder plant salinity tolerance to a greater extent when compared to sand-dominant soils.¹¹

Soil Salinity and Turfgrass Quality

Soil salinity typically reduces turfgrass growth and health. However, turfgrass species’ response to salinity exposure varies depending on genetics and expression of certain tolerance mechanisms. Only a few dozen grass species from the Poaceae family are used as turfgrasses, and these turfgrasses vary from salinity-intolerant to halophytes (salt-loving/tolerant plants) interspecifically (between different species) and intraspecifically (between individuals of the same species).¹¹ Saline conditions induce a wide variety of physical and chemical responses inside the plant. Most of the detrimental effects of salinity are due to cellular water loss and reduced water uptake. Additionally, the disruption of ion balances, various ion toxicities, and leaf chlorosis creates adverse effects on plant metabolic processes.¹² Therefore, plant growth and development are often limited or inhibited while under salinity stress.

Turf Pest Interactions with Salinity

The direct effects of soil salinity on most turfgrass species’ physiological functions are well documented. However, due to the complexity of plant-pest and salinity interactions, the indirect effects of soil salinity on turfgrass health remain unclear. The outcome of a salinity × pest interaction is highly specific to both turfgrass species and pest salinity tolerance relative to each other. No generalization about whether soil salinity suppresses or enhances pest activity in turfgrass can be made. Prior studies have indicated both instances of pest activity and suppression in saline conditions. A review of common turfgrass pests and diseases associated with saline conditions follows below.

Rapid Blight

Labyrinthula spp. are slime molds that have previously only been associated with marine organisms. Labyrinthula zosterae historically caused the wasting disease of eelgrass (Zostera marina) in many marine estuaries.¹³ More recently, research has suggested that Labyrinthula terrestris causes rapid blight in cool-season turfgrass species.

Rapid blight primarily affects a broad range of cool season turfgrasses and typically shows increased severity of symptoms as soil salinities increase. Soil salinity problems are likely to increase in the future as competition for high-quality water, increased use of recycled water on golf courses, and drought conditions occur. As a result, turf managers need to develop management strategies that cope with the potential for increased soil salinization.¹³ The rapid blight pathogen (Labryinthula terrestris) induced increasingly severe disease symptoms on perennial ryegrass (Lollium perenne cv. Brightstar SLT) as irrigation water salinity increased.⁹ When perennial ryegrass seedlings were irrigated with 0.5 dS/m water, plants were infected but not symptomatic, even though the pathogen was present in the irrigation water. However, salinities from 0.8 to 8.0 dS/m caused symptoms to develop and increased in severity as salinity increased.⁹ Increasing salinity within irrigation water encouraged faster symptom development and lower visual turf quality as time progressed after inoculation.⁹ Symptoms of rapid blight are likely to occur in susceptible turf irrigated with water having a salinity of 0.8 dS/m and higher.

A 2006 greenhouse study examined the effect of soil salinity and rapid blight severity on cool season grasses [perennial ryegrass, Kentucky bluegrass (Poa pratensis L.), and slender creeping red fescue (Festuca rubra spp. littoralis)] with differing susceptibility to the disease.⁴ Plants were irrigated daily with solutions of 0.2, 1.3, 2.5, 3.6, and 4.8 dS/m, with or without inoculation with rapid blight. Disease severity was assessed as a percent of leaf chlorosis. Leaf chlorosis due to rapid blight was minimal on the grasses irrigated with water with salinity ≤ 1.3 dS/m. However, at salinities ≥ 2.5 dS/m, rapid blight affected each turfgrass species differently. Perennial ryegrass and Kentucky bluegrass had substantial rapid blight-induced leaf chlorosis, while slender creeping red fescue was minimally affected, exhibiting only leaf chlorosis.⁴ For all species, when the salinity of irrigation was 4.8 dS/m or more, even with no rapid blight inoculation, chlorosis was like that of rapid blight-impacted turf exposed to 2.5 dS/m.⁴ The mechanisms imparting salinity tolerance may be similar to those of rapid blight tolerance, and turf species with natural salinity tolerance may be less susceptible to rapid blight infection.

Pythium Blight

Figure 2. Symptoms and signs of pythium blight on bentgrass. Image credit: Dr. Joseph Roberts, Clemson University.

Pythium blight is a serious issue on many putting greens and can be disastrous to any golf course due to its rapid onset (figure 2). Soil salinity accelerated the onset and development of pythium blight pathogen (Pythium aphanidermatum) on ‘Penncross’ creeping bentgrass (Agrostis stolonifera) and broadened the temperature range in which the disease can occur.³ Salinity levels up to 7.1 dS/m slightly stimulated pathogen growth but decreased zoospore (spore that allows movement in water) production. Soil salinity and pythium blight exhibit a synergistic relationship, with salinity stress enhancing pythium symptom development.

Nematodes

Saline irrigation and soil salinity impact plant parasitic nematode populations. Nematodes are one of the most common turfgrass pathogens of bermudagrass (Cynodon dactylon) and seashore paspalum (Paspalum vaginatum). Seashore paspalum is a halophyte that can withstand high levels of soil salinity and salt concentration in irrigation water. The use of saline irrigation water on seashore paspalum is common in subtropical coastal areas. However, it remains unclear whether salinity directly affects nematode population health or pathogenicity.

Populations of common plant parasitic nematode species, sting (Belonolaimus longicaudatus) and lance (Hoplolaimus galeatus), were studied in seashore paspalum at increasing levels of irrigation salinity. Population density of lance nematodes declined as salinity increased, while sting populations increased when salinity exposures were moderate (10 and 15 dS/m).¹⁴ Root stunting of seashore paspalum was observed when salinity levels ranged from 0 to 10 dS/m, but at higher salinity concentrations (15 to 25 dS/m), seashore paspalum roots were similar, regardless of plant exposure to sting nematodes. On the other hand, lance nematodes caused no symptoms of damage on seashore paspalum at any salinity level.¹⁴ Nematode species may differ in their salinity tolerance. Irrigating seashore paspalum with saline water may help mitigate pressure from pathogenic nematodes.

Effects of Soil Salinity on Pest Management Practices

Plant-pest interactions are heavily moderated by outside environmental factors, such as soil salinity, that can shift such interactions in favor of the plant or pest if conditions are altered. The direction and impact of this shift depend on each organism’s relative salinity tolerance and physiological responses to higher levels of salinity. Therefore, information about the salinity tolerance of common turfgrasses and the pest species infesting them is critical to ensure quality impacts are assigned to the correct abiotic (salinity) or biotic (pest) stressor.

Identification and Management of Salinity-Pest Interactions

Symptoms of salinity stress and pests/diseases on turfgrass leaves and roots are often contrasting, and the relative magnitude of damage due to each stressor should determine which management practices are implemented. Salinity stress on most turfgrass species causes reduced metabolic function due to fluctuations in symplastic (within the cell) osmotic pressure and disturbances in ion balances.¹¹ Therefore, plant growth and development are often limited or inhibited while under salinity stress. Soil salinity issues can be identified in severe cases through the accumulation of salts on the soil surface. Saline soils appear with a white crust on the surface alongside water-stressed plants, while sodic soils may have a black powdery residue on the soil surface paired with poor soil drainage.¹⁰

Symptoms of disease on turfgrass vary greatly depending on the pathogen species. Many diseases, including rapid blight and pythium blight, cause irregular patches of discolored (grey, brown, red/bronze) and weak turfgrass with occasional signs of fungal mycelium on leaf tissue. Disease occurrence can be provoked through improper management practices such as overfertilization, improper irrigation scheduling, and poor soil management practices.¹⁵

Well-designed integrated pest management and salinity monitoring programs should be used to decrease the onset of disease and may prevent such salinity-pest interactions described previously in this article. In severe cases, effective management practices can be employed for both pest control and salinity mitigation when one can correctly identify the causal agents of both stresses. Contact a local Extension office for recommendations on best management practices for soil salinity mitigation and disease control when unsure of which stressor is contributing to poor turfgrass health. The Clemson University Cooperative Extension website (clemson.edu/extension/co) has contact information for county offices.

Soil Salinity Monitoring and Management

In areas prone to soil salinization, turfgrass managers should develop and implement a soil salinity monitoring plan. This involves using an EC meter to measure the soil salinity at consistent intervals over time (e.g., daily, weekly, bi-weekly, monthly, depending upon the salinity of irrigation water). These readings, when tracked over time, can be used to determine when to employ salinity management practices. Salinity management practices include applications of gypsum, use of leaching programs, and small core hollow-tine aerification when soil salinity exceeds 2.7 dS/m.²

Irrigation and Pesticide Efficacy

Irrigation and salinity management are always critical components of any disease management program. Some turfgrass pests are affected by saline irrigation water and soil salinity. Effective salinity management is needed to ensure pesticides applied can retain biocidal activity, as high soil salinity can increase the rate of pesticide degradation.¹⁶ Additionally, the activity of some pesticides can be influenced by the carrier water quality. The pH, presence of metal cations, and hardness of the carrier water can dramatically affect pesticide efficacy. Extreme pH values can alter the charge and affect the stability of the pesticide, while cations in the water can complex with the anionic herbicides to reduce its absorption into the plant.¹⁸ More information about the effect of carrier water quality on pesticide efficacy can be found on the label of the pesticide or by contacting a local professional.

References Cited

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3. Rasmussen SL. Effect of salinity stress on development of pythium blight in Agrostis palustris. Phytopathology. 1988;78(1495).
4. Camberato JJ, Peterson PD, Martin BS. Salinity and salinity tolerance alter rapid blight in Kentucky bluegrass, perennial ryegrass, and slender creeping red fescue. Applied Turfgrass Science. 2006;3(0).
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8. Pearson C, Basics of salinity and sodicity effects on soil physical properties. Bozeman (Montana): Montana State University Extension; 2003 [accessed 2023 March 9]. https://waterquality.montana.edu/energy/cbm/background/soil-prop.html.
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10. Sonon LS, Saha U, Kissel DE. Soil salinity testing, data interpretation and recommendations. Athens (GA): University of Georgia Cooperative Extension; 2022. Circular 1019. 6 p.
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13. Stowell LJ, Martin SB, Olsen M, Kohout M. Rapid blight: a new plant disease. St. Paul (MN): The American Phytopathological Society; 2005. APSnet Features. 11 p.
14. Hixson AC, Crow WT, McSorley R, Trenholm LE. Saline irrigation affects Belonolaimus longicaudatus and Hoplolaimus galeatus on seashore paspalum. Journal of Nematology. 2005;37:37–44.
15. Lamborn A. Turfgrass disease identification key. Gainesville (FL): University of Florida IFAS Extension Service; 2014. 3 p.
16. Kaur R, Singh D, Kumari A, Sharma G, Rajput S, Arora S. Pesticide residues degradation strategies in soil and water: a review. International Journal of Environmental Science and Technology. 2023;20(3):3537–3560.
17. Sparks DL. The chemistry of saline and sodic soils. Environmental Soil Chemistry. 2003;2:285–300.
18. Chahal G, Roskamp J, Legleiter T, Johnson B. The influence of spray water quality on herbicide efficacy. West Lafayette (IN): Purdue University Cooperative Extension Service, Purdue Weed Science; 2012. https://ag.purdue.edu/btny/purdueweedscience/wp-content/uploads/2021/02/Water_Quality.pdf.

Additional Resources

Barton M, Moss JQ, Taghvaeian S. Salinity management in home lawns. Stillwater (Oklahoma): Oklahoma State University Extension. 2017 [accessed 2023 April 17]. https://extension.okstate.edu/fact-sheets/salinity-management-in-home-lawns.html.

Pace M, Johnson P. Growing turf on salt-affected soils. Logan (Utah): Utah State University Extension. 2002 [accessed 2023 April 17]. https://extension.usu.edu/yardandgarden/research/growing-turf-on-salt-affected-sites.