Earthworm community composition, seasonal population structure, and casting activity on Kentucky golf courses

Applied Soil Ecology 75 (2014) 116–123

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Earthworm community composition, seasonal population structure, and casting activity on Kentucky golf courses Carl T. Redmond, Adam Kesheimer, Daniel A. Potter ∗ Department of Entomology, S-225 Agriculture Science Bldg. N., University of Kentucky, Lexington 40546-0091, KY, USA

a r t i c l e

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Article history: Received 22 July 2013 Received in revised form 1 November 2013 Accepted 8 November 2013 Keywords: Lumbricidae Aporrectodea trapezoides Amynthas hupeiensis Turfgrass

a b s t r a c t Earthworms can be troublesome pests on golf courses when their soil-rich casts become abundant enough to disrupt the maintenance, aesthetics, and playability of putting greens and fairways. Management of the problem is hindered by lack of knowledge of earthworm community structure on North American golf courses. We surveyed communities of endogeic earthworms inhabiting golf course fairways and putting greens in central Kentucky and tracked the seasonal population structure and casting activity of the predominant species. Seven earthworm species, six of them non-native, were identified in varying proportions from fairways of the different golf courses. Aporrectodea trapezoides (Dugès) dominated, although Allolobophora chlorotica (Savigny), Diplocardia singularis (Ude), and Amynthas sp. also were abundant on some courses. Soil characteristics (pH, percentages of sand, silt, clay, and organic matter) at fairway sample sites were not good predictors of overall earthworm density or proportionate abundance of particular species. Ap. trapezoides was found in the upper 21 cm of topsoil throughout the year except when frozen ground precluded sampling. The Ap. trapezoides population consisted mainly of adults and cocoons in late autumn and winter, and juveniles in summer. Casting by Ap. trapezoides, which also occurs on soil-based greens, was greatest in late autumn and early winter, with a secondary peak in early spring. Amynthas hupeiensis, an east Asian megascolecid earthworm, was the only species found damaging sand-based greens. Prolific casting by Am. hupeiensis continued during summer after other species’ casting activity on fairways had waned. Am. hupeiensis is established along river banks in Kentucky and neighboring states, and is used as fish bait. We hypothesize that it may be introduced onto golf courses as cocoons in river sand used for course renovations, or from bait discarded by anglers fishing in golf course ponds. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Earthworms are important to the productivity of soil systems (Lee, 1985; Edwards and Bohlen, 1996) but they can become a significant problem when they deposit soil-rich piles of fecal matter, or casts, on the surface of low-cut golf course fairways and putting greens making it nearly impossible for golf course superintendents to maintain them in a desirable playing condition (Kirby and Baker, 1995; Potter et al., 2013). Earthworm casts may be so numerous that greens cannot be mowed without first dispersing them with a brush or drag lest they quickly dull the blades of reel mowers and upset the close tolerance of reel to bed knife required for an acceptable quality of cut. Casts muddy and smother the grass when smeared or compacted by tires or foot traffic, reducing water infiltration and providing a seedbed for weed establishment (Kirby and Baker, 1995; Potter et al., 2013). High earthworm populations may also promote activity of moles (Talpidae) (Edwards et al., 1999) whose unsightly tunnels and mounds disrupt playing

∗ Corresponding author. Tel.: +1 859 257 7458; fax: +1 859 323 1120. E-mail address: [email protected] (D.A. Potter). 0929-1393/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsoil.2013.11.005

surfaces and uproot the grass, causing it to dry out and die. Casts directly affect play by disrupting the smoothness and uniformity of putting surfaces, and by affecting shots hit from fairway surfaces that are more mud than turf (Kirby and Baker, 1995; Potter et al., 2013). Those problems affect players’ perception of course quality (Kirby and Baker, 1995; Potter et al., 2013) and create pressure for golf course superintendents to try to reduce the earthworm population. Prohibition of chlordane and other broadly toxic soil insecticides was followed by resurgence of earthworm casting problems on golf courses throughout the moist temperate regions of the world (Springett, 1987; Kirby and Baker, 1995; Backman et al., 2001; Ha et al., 2010; Potter et al., 2010, 2013). Presently no chemical pesticides are labeled for earthworm control on golf courses in North America, Europe, and most other countries where the game is played, nor is registration of new synthetic vermicides likely (Potter et al., 2010). Thus, golf and sports turf managers will need to rely on natural substances (Potter et al., 2010) or modified cultural practices (Kirby and Baker, 1995; Backman et al., 2001; Potter et al., 2013) that suppress earthworms and casting to tolerable levels. However, not all earthworm species respond similarly to such practices (Kirby and Baker, 1995; Potter et al., 2013).

C.T. Redmond et al. / Applied Soil Ecology 75 (2014) 116–123 Table 1 Preliminary survey of earthworm populations (adults only) on central Kentucky golf course fairways, Fall 2011. Golf coursea

Fairway grassb

n

Arlington Champion Trace Gibson Bay Lexington CC Spring Valley % of total (n = 471)

Zoy CB CB PR PR

81 73 131 75 111

% of sampled earthwormsc AT

DS

AC

LR

AR

48.1 72.6 93.1 62.7 59.5 69.4

9.9 26.0 3.1 13.3 27.0 15.1

42.0 0.0 3.8 6.7 9.9 11.7

0.0 0.0 0.0 13.3 0.0 2.1

0.0 1.4 0.0 4.0 3.6 1.7

a GPS coordinates: Arlington (37◦ 45 36 N, 84◦ 18 42  W), Champion Trace (37◦ 58 25  N, 84◦ 37 57  W), Gibson Bay (37◦ 44 04  N, 84◦ 15 21  W), Lexington CC (38◦ 04 54  N, 84◦ 26 23  W), Spring Valley (38◦ 05 03  N, 84◦ 31 33  W). b Zoy = zoysiagrass, CB = creeping bentgrass, PR = perennial ryegrass. One of the sampled fairways at Lexington CC was creeping bentgrass. c AT = Aporrectodea trapezoides (Dugès), DS = Diplocardia singularis (Ude), AC = Allolobophora chlorotica (Savigny), LR = Lumbricus rubellus Hoffmeister, AR = Aporrectodea rosea (Savigny).

Development of sustainable tactics for managing excessive earthworm casting on golf courses is hindered by lack of knowledge of what species predominate, their site preferences, and their seasonal activity. Earthworm community structure and relationships with edaphic characteristics have been surveyed on golf course fairways in Great Britain (Binns et al., 1999; Bartlett et al., 2008), but there have been no comparable surveys in North America. Therefore, our objectives were to (1) survey endogeic earthworms communities in fairways of central Kentucky golf courses to determine rank abundance and diversity of species present and their possible relationships with soil characteristics, (2) monitor phenology and seasonal casting activity of Aporrectodea sp. (mainly Aporrectodea trapezoides, the predominant species, and (3) document observations on damage to sand-based putting greens by Amynthas hupeiensis (Michaelsen), an east Asian megascolecid species that was last reported as a golf course pest along the Atlantic seaboard some 60–80 years ago. 2. Materials and methods 2.1. Earthworm community structure in golf course fairways Earthworm populations were sampled on fairways of five and six central Kentucky golf courses in autumn (October to November) of 2011 and 2012, respectively (Tables 1 and 2). For the 2012 survey, one of the courses sampled the first year was dropped because of low casting activity, and additional ones not sampled in 2011 were added. Fairway grasses were either creeping bentgrass (Agrostis stolonifera L.), perennial ryegrass (Lolium perenne L.), or zoysiagrass (Zoysia japonica Steud.); those species are representative of the grasses used on golf course fairways in the United States’ transitional climatic zone (Beard, 2002). With one exception (Lexington CC 2011, Table 1) all fairways on a given course consisted of a single species of grass. Three fairways per course that had noticeable casting activity were selected for sampling. We excluded par-3 holes which typically have short fairways that may or may not be managed the same as those of longer holes, and included at least one fairway associated with the front (1–9) or back (10–18) nine holes on each course. For sampling, slabs of turf and soil (18 × 18 cm, 21 cm deep) were cut and removed with flat-blade spades, broken apart by hand, and sorted for earthworms in the field. We used digging and hand-sorting, rather than mustard extraction, because the latter method may be less efficient for assessing size and structure of earthworm populations (Bartlett et al., 2006) especially in the relatively compacted clay or silt–loam soils that are typical on Kentucky golf courses (authors’ unpublished data). Most samples were taken

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along the sides of fairways, within 1–2 m from the edge and several meters apart. Sampling continued until 30 clitellate (adult) earthworms had been collected from that fairway, along with whatever juvenile (non-clitellate) earthworms were found. Most samples contained no more than two adults. At least four samples were excavated per fairway. If 30 adults were not found after 30 samples, or if no adults were found after 10 samples were taken, that partial collection was discarded and a different fairway was selected for sampling. The number of samples needed to reach 30 adults was recorded for each fairway. Samples were pooled within fairways, placed in containers with soil from the collection sites, and brought to the laboratory for identification. Earthworms were identified fresh when possible, or preserved in formalin-free fixative (Accustain, Sigma-Aldrich, St. Louis, MO) until they could be examined with a dissecting microscope and identified A soil sampling probe was used to extract 20 soil cores (2 cm diameter, 7.5 cm deep) from the same area of each fairway where the earthworms were collected. The first 6 cm of topsoil under the thatch–soil interface was broken off, consolidated in cardboard containers, dried, and analyzed at the University of Kentucky (UK) Regulatory Services Soil Testing Laboratory for pH, plant available micronutrients, and percentages of sand, silt, clay, and organic matter. Soil samples from the three fairways per golf course were consolidated in 2011, providing a composite analysis of the soil from each course. In 2012, once the extent of variation in earthworm assemblages on different fairways of the same course had become clear, separate analyses were done for each of the 18 sampled fairways to provide greater statistical power in testing possible relationships between earthworm abundance and site soil characteristics. Adult earthworms were identified using published and on-line keys (Olson, 1928; Schwert, 1990; Snyder, 2010). Aporrectodea sp. (Oligochaeta: Lumbricidae) are difficult to differentiate because of their morphological similarity and variability, so their phylogenetic relationships and nomenclature have long been debated (Reynolds, 1995; Edwards and Bohlen, 1996; Pérez-Losada et al., 2009; Fernández et al., 2012). Recent phylogenetic assessment based on mitochondrial and nuclear DNA sequences (Pérez-Losada et al., 2009) confirmed that what has been referred to as “Aporrectodea caliginosa species complex” consists of at least five valid species: Aporrectodea turgida (Eisen), Ap. trapezoides, Aporrectodea tuberculata (Eisen), Aporrectodea longa (Ude), and Aporrectodea nocturna (Evans). Of those species previously reported from Kentucky (Reynolds, 2008), Ap. trapezoides and Ap. turgida are common, whereas Ap. tuberculata occurs mainly at high elevation. Ap. trapezoides is more likely than Ap. turgida to be associated with casting (Reynolds, pers. communication). Earthworms that keyed (Schwert, 1990; Snyder, 2010) to A. caliginosa are herein referred to as Ap. trapezoides, recognizing the possibility that some Ap. turgida might also have been represented in that group. Individuals of an Amynthas sp. (Oligochaeta: Megascolecidae) were encountered in some fairways during the autumn 2011 survey but we did not collect them because all of them appeared to be juveniles. Subsequently we learned to recognize juveniles belonging to that genus by their distinctive greenish coloration and perichaetine setal arrangement (Reynolds, pers. communication), so they were included in the 2012 survey. 2.2. Seasonal variation in population structure of Aporrectodea trapezoides in Kentucky Earthworm population structure can provide insight about seasonal patterns of reproduction, development, and other activities in the soil (James, 1992). We monitored population structure of Ap. trapezoides in the topsoil, including overall abundance, proportionate representation of particular life stages, and cocoon

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Table 2 Survey of earthworm populations on central Kentucky golf course fairways, Fall 2012. Golf coursea

Fairway grassb

n

Arlington Champ. Trace Gibson Bay Kearney Hills Spring Valley UK Club % of total (n = 650)

Zoy CB CB CB PR CB

107 110 98 99 109 127

a b c d

% of sampled earthwormsc AT 49.1 63.6 64.3 44.4 31.2 45.7 49.5

AC 12.0 0.0 15.3 52.5 16.5 52.8 25.4

DS 38.0 14.5 20.4 3.0 1.8 0.0 12.6

Am 0.0 20.9 0.0 0.0 50.5 0.0 12.0

AR 0.0 0.9 0.0 0.0 0.0 1.6 0.5

Simpson’s diversityd 0.60 0.53 0.53 0.53 0.61 0.52

GPS coordinates: Kearney Hills (38◦ 07 14  N, 84◦ 32 04  W), UK Club (38◦ 06 56  N, 84◦ 36 30  W), other courses, see Table 1. Zoy = zoysiagrass, CB = creeping bentgrass, PR = perennial ryegrass. AT = Aporrectodea trapezoides (Dugès), AC = Allolobophora chlorotica (Savigny), DS = Diplocardia singularis (Ude), Am = Amynthas sp., AR = Aporrectodea rosea (Savigny). Simpson’s Index of Diversity, pooled data from three fairways per course; value = probability that two individuals randomly sampled will belong to different species.

production, for 12 months (November 2011 to October 2012) in a 0.25 ha sward of creeping bentgrass maintained at fairway height at the University of Kentucky A. J. Powell Turfgrass Research Center [AJPTRC], Lexington, KY (38◦ 07 48 N, 84◦ 30 02 W). The underlying soil is a Maury silt loam (fine, mixed, mesic typic Paleudalf; pH 5.7) containing 3.9% organic matter and texture consisting of 22.9% sand, 54.5% silt, and 22.6% clay. Fifteen replicate plots were established, each with 12 subplots (1.0 m2 ) that were randomly assigned a sampling date so that each subplot was sampled only once during the year. Sampling consisted of cutting a slab of turf and soil (18 × 18 cm, 21 cm deep) from the center of each subplot and hand-sorting and counting all earthworm life stages present, including cocoons. Samples were brought to the laboratory for identification. In the laboratory, earthworms were cleaned of soil by washing in tap water, blotted to remove excess water, and allocated to one of four categories (McCredie et al., 1992) based on their sexual maturity: (1) juveniles without sexual features, (2) tubercula pubertatis, where only the tubercula pubertatis were visible as pale raised areas, (3) clitellum-developing, possessing the tubercula pubertatis and dorsal surfaces above that structure becoming smooth, continuous, and reddish-brown, and (4) clitellate (adult), possessing a creamy turgid clitellum. Earthworms were identified using the aforementioned keys. Immature specimens (except for Amythnas sp. which have distinctive juveniles) and most damaged adults were not identifiable.

2.3. Seasonal pattern of Aporrectodea trapezoides casting activity Earthworm casting activity was monitored on a 29 × 29 m stand of ‘Penncross’ creeping bentgrass (about 75%) and annual bluegrass, Poa annua L. (about 25%) established in 1978 and managed as a push-up golf putting green at the AJPTRC. The soil there is a Maury silt loam (fine, mixed, mesic typic Paleudalf) with a pH of 6.3. The soil type is homogeneous and original, and no sand topdressing has been applied. It was mowed five times per week at 4.0 mm height of cut during the growing season and as needed at other times, and irrigated from a permanent sprinkler system to prevent visible stress. Earthworms at the site are almost all Ap. trapezoides, with a relatively small number of L. terrestris also present (Potter et al., 2010). The site has a slight west to east slope which causes the upper portion to dry faster and have fewer earthworm casts than occur on the downside of the slope. Five plots (1.0 m2 ) with 1.0 m borders were established and marked on each end of the stand. Earthworm casts were counted bi-weekly for 52 weeks beginning in late August 2011. On each census date a frame (1 × 1 m) made from PVC pipe was placed over each plot and the number of casts within was counted. Counts were always taken one day after mowing. Only fresh casts, not ones that had been compacted and smeared by mowing activities, were

counted. Counts were not taken if the ground was frozen or snow covered. Rainfall and air temperature data were obtained from a University of Kentucky Weather Center Station at the AJPTRC study site. Data are reported in biweekly increments as mean daily averages. The soil green upon which casting was monitored and the adjacent fairway-height turf (Section 2.2) received supplemental irrigation from April through October 2012 as needed to prevent visible drought stress. 2.4. Observations of Amynthas hupeiensis in sand-based putting greens In summer 2012 we received reports of very heavy casting on two sand-based greens at the AJPTRC and on most greens at a nine-hole rural golf course in Powell County, KY (37◦ 51 52 N, 83◦ 54 01 W), about 66 km east of Lexington, KY. Casting by the ubiquitous Ap. trapezoides is usually not a problem on putting greens with high-sand root zones built to United States Golf Association specifications (Potter et al., 2013; authors’ observations), nor does it normally extend into summer. We visited the sites in July and August 2012 and collected 30-earthworm samples from both AJPTRC greens and three sand-based greens at the golf course by removing 15-cm deep cores with a golf cup cutter positioned over fresh casts. All of the earthworms were muddy green in color, appeared to be a single morphotype, and keyed to the genus Amynthas. Additional samples of adults were collected from the same sites in May 2013, after casting had resumed, and from fairways of two of the golf courses (Spring Valley and Champion Trace) in the main survey where the greenish Amynthas sp. juveniles had been found. We observed the casts in situ and interviewed the golf superintendent about the history of the problem at the Powell County site. Members of the golf course grounds crew told us of a site along banks of the nearby Red River, <2 km from the course, where local anglers dig “green stinkworms” for catfish bait. We accompanied them to that site and collected about 30 adult specimens. We also returned in late summer 2013 to two of the golf courses (Spring Valley and Champion Trace) where Amynthas sp. juveniles had been found in the 2012 survey and collected adult specimens from the same fairways. Those earthworms, together with specimens of the adult Amynthas collected from sand-based putting greens at the Powell County golf course and the Red River bank were sent to specialists (G. Damoff, Stephen F. Austin State University, Nacogdoches, TX; B. Snyder, Kansas State University, Manhattan KS; and S. James, University of Iowa, Iowa City, IA) who identified them. 2.5. Data analyses Relative abundance of earthworm species was tabulated by course and fairway in each year. Simpson’s diversity index [1 − D;

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where D = pi 2 and pi = the proportion of individuals in the ith species] was calculated for the pooled fairway samples from each golf course in 2012, and relative dominance of particular species was clarified by rank–abundance analysis (Magurran, 2004). Relationships between site soil characteristics and earthworm abundance or prevalence of particular species from the 2012 survey were tested using linear regression analysis. Analyses were done with Statistix 9 (Analytical Software, 2008). Data are reported as means ± standard error (SE).

3. Results 3.1. Earthworm community structure in golf course fairways Seven species of topsoil-dwelling earthworms were identified in varying proportions from the different golf courses from a total sample of 471 and 651 identifiable specimens in 2011 and 2012, respectively (Tables 1 and 2). The communities were dominated by Ap. trapezoides. Only a few L. terrestris were represented, doubtless because that deep-burrowing species would not have been

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collected by our sampling method. Diplocardia singularis and Am. hupeiensis belong to the families Acanthodrilidae and Megascolecidae, respectively, whereas all of the other found species belong to the family Lumbricidae (Reynolds, 2008). All of the species other than Ap. rosea had previously been reported from Kentucky (Reynolds, 2008), although not in association with golf courses. Proportionate abundance of Ap. trapezoides was similar across golf courses (one-way ANOVA with fairways as replicates; F = 0.58, df = 5, 12; P > 0.70; 2012 survey data), as was Simpson’s Index of Diversity (Kruskal–Wallis test, P > 0.9), but the percentages (of total individuals) comprised of Al. chlorotica or Amynthas sp. differed from course to course (Kruskal–Wallis test, P < 0.05). Species composition often varied on different fairways of the same course (Fig. 1). Soil characteristics for the 18 golf course fairways sampled in 2012 were as follows (mean ± SE (range)): 24.8 ± 1.4% sand (19–39); 58.8 ± 1.9% silt (40–68); 16.4 ± 1.0% clay (12–29); 7.5 ± 0.3% organic matter (5–10); 5.8 ± 0.1 pH (5.0–6.8). Analysis of variance for slope of linear regression showed no significant relationships between overall earthworm density and any of those parameters (F1,16 ≤ 0.13, P > 0.73). Although there weak

Fig. 1. Variation in proportional abundance of four earthworm species in samples from fairways of six central KY golf courses, 2012. AT = Aporrectodea trapezoides (Dugès), AC = Allolobophora chlorotica (Savigny), Am = Amynthas sp., DS = Diplocardia singularis (Ude).

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Fig. 2. Upper graph: Changes in the population structure of Aporrectodea trapezoides (Dugès) under fairway-height creeping bentgrass in Lexington, KY during 2011–2012; J = juveniles, TP = tubercula pubertatis visible as pale raised area, CD = clitellum developing, C = clitellate adults. Middle and lower graphs: Seasonal fluctuation in density of earthworms and cocoons in the upper 21 cm of soil.

correlations for Al. chlorotica to be proportionately less abundant at sites having more relatively more acidic or sandy soils (P = 0.05, 0.10; r2 = 0.22, 0.16, respectively), and for D. singularis to be slightly more abundant in relatively more acidic soils (P = 0.02, r2 = 0.27), none of the soil physiochemical parameters was a strong predictor of earthworm community composition. There also were no significant relationships (P ≥ 0.25) between overall earthworm density or proportionate abundance of particular species and individual soil elements (Ca, P, K, Mg, Zn; data not shown). 3.2. Seasonal variation in population structure of Aporrectodea trapezoides in Kentucky Earthworms were found in the upper 21 cm of topsoil throughout the year except for January when the frozen ground precluded sampling (Fig. 2). Relative proportions of juvenile, semi-mature (i.e., with tubercula pubertatis, but still lacking fully-developed clitellum), and adult earthworms changed during the year. The population consisted mainly of adult (fully clitellate) and semimature individuals in late autumn and winter, and juveniles in summer (Fig. 2). Cocoons were scarce during summer, becoming more abundant in October and coinciding with an upsurge of casting in autumn (Figs. 2 and 3). Although cocoons were found throughout late autumn and winter, they were most abundant in March, coinciding with heavy casting in late winter and early spring on a nearby soil-based putting green (see below). The dip in

Fig. 3. Seasonal casting activity by Aporrectodea trapezoides (Dugès) on a soil-based creeping bentgrass putting green in Lexington KY (upper graph) in relation to biweekly mean temperature and precipitation.

numbers of earthworms and cocoons in the April samples (Fig. 2) probably reflects the unseasonably hot and dry weather preceding the early April sample date (9 days with ≥24 ◦ C air temperature between 15 and 30 March; only 2.8 cm of rain from 18 March to 3 April, mostly on 23 March). 3.3. Seasonal pattern of Aporrectodea trapezoides casting activity Casting was greatest in late autumn and early winter, with a secondary peak in early spring (Fig. 3). Almost no casting occurred during summer (June to September) despite the soilbased green upon which casting was monitored having received regular irrigation to maintain turf vigor. Casting activity, when summarized biweekly, more closely tracked soil and air temperatures than rainfall, but during those months when it occurred there usually was an upsurge in casting for 1–2 days after rains. The greatest activity occurred when soil temperatures were 5–12 ◦ C (Fig. 4a). 3.4. Observations of Amynthas hupeiensis in sand-based putting greens All specimens associated with heavy casting on sand-based greens were identified as Am. hupeiensis, (formerly Pheretima hupeiensis Michaelson), a species that was first reported from Kentucky by Gates (1963, as P. hupeiensis) and that also occurs in other Midwestern states (Reynolds, 2008). We observed Am. hupeiensis to produce casts by both day and night and during all four

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Fig. 4. (A) Prolific casting by Amynthas hupeiensis (Michaelson) on a sand-based putting green in Powell Co., KY; (B) Sinuate form of Am. hupeiensis cast on sand-based putting green. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

seasons, including summer, the highest activity occurring from mid-spring until autumn well after casting by Ap. trapezoides had waned (Fig. 4a). After greens were mowed in the morning, dispersing the casts, substantial numbers of new casts were produced by that afternoon. Am. hupeiensis casts on sand-based putting greens were sandy and typically more sinuate (Fig. 4b) than the piles of smooth compact pellets deposited by Ap. trapezoides on the moist native soils of Kentucky golf course fairways. The “green stinkworms” collected along banks of the Red River, and the adult Amynthas sp. collected in late summer 2013 from fairways two of the golf courses where Amynthas juveniles were found in the 2012 survey were identified as Am. hupeiensis. 4. Discussion With the exception of D. singularis all of the earthworms we found on central Kentucky golf courses are exotic peregrine species. Ap. trapezoides and Al. chlorotica which were spread from northern and western Europe by human activities in the past few hundred years, are among the dominant earthworms of agricultural and pastoral soils throughout moist temperate regions of the world (Lee, 1985; Edwards and Bohlen, 1996). Both are endogeic species that make continuous, extensive, subhorizontal burrows in the upper 10–15 cm of soil (Edwards and Bohlen, 1996). Aporrectodea sp. also are a major component of the earthworm communities inhabiting golf course fairways and other grassland soils in Great Britain (Binns et al., 1999; Bartlett et al., 2008), New Zealand (Springett, 1987), and Australia (McCredie et al., 1992). D. singularis, one of three Diplocardia sp. known to occur in Kentucky (Reynolds, 2008), had previously been recorded only from the western extremes of the state. This

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is the first report of D. singularis inhabiting golf courses. Tu et al. (2011) found an unidentified Diplocardia sp. casting on a creeping bentgrass tee box in North Carolina. Lumbricus terrestris, an anecic species that casts on the surface around the burrow entrance also occurs on Kentucky golf courses (authors’ observations) but because of its deep-burrowing behavior it would not have effectively been collected by digging and handsorting, our sampling method. However, L. terrestris was also much less abundant than Aporrectodea sp. in earlier studies in which irritant drenches, including formalin, mustard, or tea seed saponins, were used for sampling (Potter et al., 1990, 1994; Kunkel et al., 1999; Potter et al., 2010; Larson et al., 2012). Also, nearly all of the casts we observed on fairways and on the soil green were much smaller, with a narrower burrow opening, than is typical for L. terrestris. Our observations, including sampling beneath casts, indicate that endogeic earthworms, especially Ap. trapezoides, are responsible for most of the casting problems on fairways of Kentucky golf courses. Ap. trapezoides, Al. chlorotica, and the other endogeic earthworm species found in our surveys thrive in moist soils that are rich in organic matter (Lee, 1985), so their rates of reproduction in golf course fairways are likely to be high. Allowing for latitudinal differences, the seasonal activity of Ap. trapezoides in Kentucky is similar to that reported for endogeic Aporrectodea sp. in English pastures (Evans and Guild, 1947), with main casting periods during cool moist periods from autumn to early winter, and from late winter to mid-spring, and cocoons abundant in winter and spring but scarce in summer. It is possible that the decline in Ap. trapezoides abundance, particularly that of mature individuals, in the summer months may have been partly due to the larger adults moving deeper into the soil profile than 21 cm. Presence of cocoons throughout the year, especially during all months when there is heavy casting, is probably one of the reasons why populations rebound relatively soon after suppression by short-residual pesticides (e.g., Potter et al., 1990, 1994). Edaphic factors including pH, or percentages of sand, silt, clay, or organic matter were not good predictors of overall earthworm density or proportionate abundance of particular species inhabiting fairways of central Kentucky golf courses. Bartlett et al. (2008), in contrast, found a strong inverse relationship between sand content of fairway soils and overall earthworm density on five English golf courses, but there the levels of sand and range in sandiness (45–88%) were much higher than the 19–39% sandiness we found in central Kentucky golf course fairway soils. Soil moisture doubtless limits earthworm spatial distributions on golf courses, but all of the sampled fairways were under irrigation. Similarly, all of the fairways were regularly mowed, with clippings returned, so food in the form of soil organic matter is unlikely to have been limiting. Aporrectodea sp. and Allolobophora sp., peregrine species that have become dominant in agricultural lands, pastures, turf, and gardens throughout much of the temperate world (Lee, 1985), are unlikely to be constrained by the relatively favorable characteristics of central Kentucky golf course fairway soils. Amynthas sp., which have been exported from eastern and southeastern Asia to North America and other regions of the world (Reynolds, 1994; James and Hendrix, 2004; Hendrix et al., 2008), are the main surface-casting species impacting golf courses in South Africa (Mostert et al., 2002) and in South Korea (Ha et al., 2010), and also are dominant members of the earthworm fauna of Taiwan (Tsai et al., 2000) and Japan (Blakemore, 2003). Two Amynthas species, Am. corticis (Kinberg) [formerly Am. diffringens (Baird)] and Am. hupeiensis (Michaelsen) had previously been reported from a few widely-distributed Kentucky counties (Reynolds, 2008). Both of those species have also been reported from neighboring states (Reynolds, 2008).

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During the 1930s to 1950s, outbreaks of an earthworm reported as Pheretima (=Amynthas) hupeiensis and referred to as the “Oriental earthworm” “tropical earthworm” or “stinkworm” caused significant damage to golf courses along the Atlantic seaboard from Connecticut to Virginia (Anonymous, 1948; Schread, 1950a,b, 1952). The earthworms were active during warm moist weather and their prolific casting during both daylight and night made it nearly impossible to maintain putting greens in a desirable playing condition. The pest was unresponsive to control with mowrah meal, mercury compounds, lead arsenate, DDT, and most other substances used for earthworm control at that time, but was eventually controlled by high rates of the now-defunct pesticides chlordane, aldrin, toxaphene, or parathion (Schread, 1950b, 1952). There apparently have been no published accounts of Am. hupeiensis as a golf course pest since the 1950s. Our observations of Am. hupeiensis infestations on sand-based putting greens in Kentucky are generally consistent with early accounts of the problem from Connecticut (Schread, 1950a,b, 1952). The superintendent and staff of the Powell County, KY golf course where we observed the most egregious casting by Am hupeiensis (Fig. 4a) first noticed the problem about 6–12 months after the greens were renovated with sand dredged from banks of the Ohio River (personal communication). Invasive Amynthas spp. are dug, sold, and transported as fish bait and may become established around river banks as a result of anglers discarding unused bait (Callaham et al., 2003, 2006). They are sometimes purposely introduced to establish bait populations convenient to such areas (Callaham et al., 2003). Am. hupeiensis, which is favored for catfish bait in the central United States, is easy to find at public river access sites and near road bridges (James, 2011). We hypothesize that Am. hupeiensis cocoons may have been transported in the river sand used for course renovations. Most Amynthas are parthenogenetic so even a single cocoon or individual could establish a population (Hendrix et al., 2008). Although we do not have access to the Ohio River dredge sites, we readily collected Am. hupeiensis from banks of the Red River, at a site frequented by local anglers, a short distance from the Powell County golf course. Am. hupeiensis or other Amynthas species might also be introduced by anglers fishing in golf course lakes, ponds, and streams. Critical experiments are needed to test those hypotheses, but if supported, further research may point to ways to avoid introducing these troublesome Asian earthworms onto golf courses. Acknowledgments The authors thank G. A. Damoff (Stephen F. Austin State University, Nacogdoches, TX), B. A. Snyder (Kansas State University, Manhattan KS), and S. W. James (University of Iowa, Iowa City, IA) for identifying specimens of Amynthas hupeiensis, and three anonymous reviewers for constructive criticism. J. W. Reynolds (Oligochaetology Laboratory, Kitchener, Ontario) provided valuable advice about earthworms in Kentucky. We also thank D. W. Williams (University of Kentucky) and the Kentucky golf course superintendents who granted access to study sites. This is paper number 13-08-078 of the Kentucky Agricultural Experiment Station. References Analytical Software, 2008. Statistix 9.0. Analytical Software, Tallahassee, FL. Anonymous, 1948. The tropical earthworm. U.S. Golf Assoc. J. Autumn. Backman, P.A., Miltner, E.D., Stahnke, G.K., Cook, T.W., 2001. Effects of cultural practices on earthworm casting on golf course fairways. Int. Turfgrass Soc. Res. J. 9, 3–7. Bartlett, M.D., James, I.T., Harris, J.A., Ritz, K., 2008. Earthworm community structure on five English golf courses. Appl. Soil Ecol. 39, 336–341.

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