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L.E. Trenholm, R.N. Carrow and R.R. Duncan

Damage from traffic can seriously injure athletic field turfgrass, although fertility regimes can influence wear tolerance. While excess nitrogen (N) can reduce wear tolerance, moderate N has improved tolerance and hastened recovery from injury. Potassium (K) may enhance wear tolerance through regulation of turgor potential. This research was undertaken to determine shoot growth and wear tolerance of seashore paspalum (Paspalum vaginatum Swartz) to N and K application. Field studies were conducted in 1998 at the Univ. of Georgia Experiment Station, Griffin. Grasses were established on U.S. Golf Association specification greens in 1996. Fertility treatments were applied at annual N rates of 196 and 392 kg·ha-1 and K rates of 92 and 392 kg·ha-1. The higher N rate increased wear tolerance, shoot growth, shoot density, visual quality, and color of the two ecotypes, AP 10 and AP 14, but reduced their visible range spectral reflectance, indicating greater absorption of photosynthetically active radiation (PAR). Measured responses to K were minimal and no enhancement of wear tolerance in response to K treatment was noted.

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S.K. Braman, R.R. Duncan and M.C. Engelke

Turfgrass selections including 21 paspalums (Paspalum vaginatum Swartz) and 12 zoysiagrasses (Zoysia sp.) were compared with susceptible `KY31' tall fescue (Festuca arundinacea Schreb.) and more resistant common bermudagrass (Cynodon dactylon Pers.) and common centipedegrass [Eremochloa ophiuroides (Munro.) Hack] for potential resistance to fall armyworm [Spodoptera frugiperda (J.E. Smith)], an occasionally serious pest of managed turf. Turfgrass and pasture grasses annually suffer sporadic damage by this pest, often severe in the Gulf Coast states. Resistant grasses offer an alternative management tool for the fall armyworm, reducing the need for pesticide use. Laboratory evaluations assessed the degree of antibiosis and nonpreference present among more than 30 turfgrass genotypes to first and third instar fall armyworms, respectively. Zoysiagrasses exhibiting high levels of antibiosis included `Cavalier', `Emerald', DALZ8501, DALZ8508, `Royal', and `Palisades'. Paspalum selections demonstrating reduced larval or pupal weights or prolonged development times of fall armyworm included 561-79, Temple-2, PI-509021, and PI-509022.

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Geungjoo Lee, Ronny R. Duncan and Robert N. Carrow

Evaluation of turfgrass salt tolerance is a basic strategy for selecting grasses that can be grown in areas with salt-affected water or soils. Our objectives were to determine the relative salinity tolerances of 32 grasses and to evaluate potential shoot-based criteria for assessing salinity tolerance. Shoot growth responses to salinity of 28 seashore paspalums (Paspalum vaginatum Swartz) and four bermudagrass [Cynodon dactylon (L.) × C. transvalensis Burtt-Davy] cultivars were investigated under solution/sand culture in a greenhouse. Turfgrasses were grown in a sea-salt amended nutrient solution. Salinity ranges were 1.1 to 41.1 dS·m-1 based on electrical conductivity of the solution (ECw). Selection criteria to assess salt tolerance were absolute growth at 1.1 (ECw0), 24.8 (ECw24), 33.1 (ECw32), and 41.1 dS·m-1 (ECw40); threshold ECw; ECw for 25% and 50% growth reduction based on ECw0 growth; and leaf firing (LF) at ECw0 and ECw40 (LF0 and LF40, respectively). Significant variations among 32 entries were observed for all shoot responses except threshold ECw. Ranges of values for shoot parameters were: inherent growth at ECw0 = 0.10 to 0.98 g dry weight (10-fold difference); growth at 24.8 dS·m-1 = 0.11 to 0.64 g; growth at 33.1 dS·m-1 = 0.09 to 0.54 g; growth at 41.4 dS·m-1 = 0.06 to 0.35 g; threshold ECW = 3.9 to 12.3 dS·m-1; ECw25 % = 14 to 38 dS·m-1; ECw50% = 22 to 43 dS·m-1; and LF40 = 7% to 41%. Results in this study indicated substantial genetic-based variation in salt tolerance within seashore paspalums. When evaluation of salt tolerance based on shoot responses is attempted at wide salinity levels up to 40 dS·m-1, all seven criteria exhibiting a significant F test can be used. Five entries (SI 92, SI 93-1, SI 91, SI 93-2, SI 89) were ranked in the top statistical grouping for all seven-growth parameters, followed by SI 90 ranked in six out of seven, and three paspalums (SI 94-1, `Sea Isle 1', and `Taliaferro') were ranked in five out of seven categories.

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Geungjoo Lee, Robert N. Carrow and Ronny R. Duncan

Seashore paspalum (Paspalum vaginatum Swartz) is a warm season turfgrass that survives in sand dunes along coastal sites and around brackish ponds or estuaries. The first exposure to salt stress normally occurs in the rhizosphere for persistent turfgrass. Information on diversity in salinity tolerance of seashore paspalums is limited. From Apr. to Oct. 1997, eight seashore paspalum ecotypes (SI 94-1, SI 92, SI 94-2, `Sea Isle 1', `Excalibur', `Sea Isle 2000', `Salam', `Adalayd') and four bermudagrass (Cynodon dactylon × C. transvaalensis Butt-Davy) cultivars (`Tifgreen', `Tifway', `TifSport', `TifEagle') were investigated for levels of salinity tolerance based on root and verdure responses in nutrient/sand culture under greenhouse conditions. Different salt levels (1.1 to 41.1 dS·m-1) were created with sea salt. Measurements were taken for absolute growth at 1.1 (ECw0; electrical conductivity of water), 24.8 (ECw24), 33.1 (ECw 32), and 41.1 dS·m-1 (ECw40), threshold ECw, and ECw for 25% growth reduction from ECw0 growth (ECw25%). Varying levels of salinity tolerance among the 12 entries were observed based on root, verdure, and total plant yield. Ranges of root characteristics were inherent growth (ECw0) = 0.20 to 0.61 g dry weight (DW); growth at ECw24 = 0.11 to 0.47 g; growth at ECw32 = 0.13 to 0.50 g; growth at ECw40 = 0.13 to 0.50 g; threshold ECw = 3.1 to 9.9 dS·m-1; and ECw25% = 23 to 39 dS·m-1. For verdure, ranges were inherent growth at ECw0 = 0.40 to 1.07 g DW; growth at ECw40 = 0.31 to 0.84 g; and ratio of yields at ECw40 to ECw0 = 0.54 to 1.03. Ranges for total growth were inherent growth at ECw0 = 0.72 to 2.66 g DW; growth at ECw24 = 0.55 to 2.23 g; growth at ECw32 = 0.54 to 2.08 g; growth at ECw40 = 0.52 to 1.66 g; threshold ECw = 2.3 to 12.8 dS·m-1; and ECw25% = 16 to 38 dS·m-1. Significant salinity tolerance differences existed among seashore paspalums and bermudagrasses as demonstrated by root, verdure, and total growth measurements. When grasses were ranked across all criteria exhibiting a significant F test based on root, verdure, and total growth, the most tolerant ecotypes were SI 94-1 and SI 92. Salinity tolerance of bermudagrass cultivars was relatively lower than SI 94-1 and SI 92. For assessing salinity tolerance, minimum evaluation criteria must include absolute growth at ECw0 and ECw 40 dS·m-1 for halophytes, but using all significant parameters of root and total yield is recommended for comprehensive evaluation.

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Yiwei Jiang, Robert N. Carrow and Ronny R. Duncan

Turfgrasses are often exposed to different shade environments in conjunction with traffic stresses (wear and/or compaction) in athletic fields within stadiums. The objective of this study was to assess the effects of morning shade (AMS) and afternoon shade (PMS) alone and in combination with wear and wear plus soil compaction on `Sea Isle 1 seashore paspalum (Paspalum vaginatum Swartz). The study was conducted using two consecutive field trials under sports field conditions from 9 July to 10 Sept. 2001 at the Univ. of Georgia Experiment Station at Griffin. “T” shaped structures constructed of plywood on the sports field were used to provide §90% morning and afternoon shade, respectively, and were in place for 1 year prior to data accumulation. A wear device and a studded roller device simulated turfgrass wear (WD) and wear plus soil compaction (WSC), respectively, to the shaded plots. Only minor differences in turf color, density, or canopy spectral reflectance were found between AMS and PMS under no-traffic treatments in both trials. Grasses under WD generally recovered faster than those exposed to WSC across all light levels, including full sunlight (FL), AMS, and PMS. AMS combined with WD treatment had an average 9% higher rating of color, 11% higher density, and 28% less tissue injury than that of PMS with WD at 7 days after traffic treatment (DAT). Compared to PMS with WSC treatment at 7 DAT, AMS with WSC had 12% higher rating of color, 9% higher density, and 4% less tissue injury. AMS with WD treatment exhibited 11% higher normalized difference vegetation index (NDVI), 4% higher canopy water band index (CWBI), and 13% lower stress index than that of PMS with WD at 7 DAT. AMS with WSC, relative to PMS with WSC, demonstrated 8% higher NDVI, 3% higher CWBI, and 8% lower stress index at 7 DAT. Re sults indicated that AMS (i.e., afternoon sunlight) had less detrimental influences than PMS (i.e., morning sunlight) on turfgrass performance after it was subjected to wear stress or wear plus soil compaction.

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Yiwei Jiang, Robert N. Carrow and Ronny R. Duncan

Traffic stresses often cause a decline in turfgrass quality. Analysis of spectral reflectance is valuable for assessing turfgrass canopy status. The objectives of this study were to determine correlations of narrow band canopy reflectance and selected reflectance indices with canopy temperature and turf quality for seashore paspalum exposed to wear and wear plus soil compaction traffic stresses, and to evaluate the effects of the first derivative of reflectance and degree of data smoothing (spectral manipulations) on such correlations. `Sea Isle 1' seashore paspalum (Paspalum vaginatum Swartz) was established on a simulated sports field during 1999 and used for this study. Compared to original reflectance, the first derivative of reflectance increased the correlation coefficient (r) of certain wavelengths with canopy temperature and turf quality under both traffic stresses. Among 217 wavelengths tested between 400 and 1100 nm, the peak correlations of the first derivative of reflectance occurred at 661 nm and 664 nm for both canopy temperature and turf quality under wear stress, respectively, while the highest correlations were found at 667 nm and 820 to 869 nm for both variables under wear plus soil compaction. Collectively, the first derivative of reflectance at 667 nm was the optimum position to determine correlation with canopy temperature (r > 0.62) and turf quality (r < -0.72) under both traffic stresses. All correlations were not sensitive to degrees of smoothing of reflectance from 400 to 1100 nm. A ratio of R936/R661 (IR/R, Infrared/red) and R693/759 (stress index) had the strongest correlations with canopy temperature for wear (r = -0.63) and wear plus soil compaction (r = 0.66), respectively; and a ratio of R693/R759 had the strongest correlation with turf quality for both wear (r = -0.89) and wear plus soil compaction (r = -0.82). The results suggested that the first derivative of reflectance could be used to estimate any single wavelength simultaneously correlated with multiple turf canopy variables such as turf quality and canopy temperature, and that the stress index (R693/R759) was also a good indicator of canopy stress status.

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J. Wolpert, E. Weber, R. Duncan, D. Hirschfelt and M. Anderson

Petioles were gathered at bloomtime in four trials, one each of `Chardonnay and `Zinfadel' and two of `Cabernet Sauvignon' over 2 years, 1993 and 1994. In each trial, scions were grafted onto 12 to 14 rootstocks. Petioles were analyzed for NO3-nitrogen, NH4-N, K, P, and Mg. NO3-N levels differed among rootstocks by as much as 16-fold (126 to 2064 μg·g–1), NH4-N by as much as 4-fold (253 to 1-28 μg·g–1), K, P, and Mg by about 3-fold (9.7 to 30.6 mg·g–1, 1.8 to 6.3 mg·g–1, and 2.9 to 7.5 mg·g–1, respectively). `Freedom' had the highest levels of NO3-N. `Salt Creek' had moderate levels of NO3-N, but had the highest levels of NH4-N. The rootstock 420A Mgt was consistently low in NO3-N, NH4-N, and K. Freedom was among the highest in K content. The rootstock 44-53 Malègue' had high levels of K and low Mg. Implications for vineyard fertilization programs will be discussed.

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Jason A. Ferrell, Timothy R. Murphy, Ron R. Duncan and William K. Vencill

The usage of seashore paspalum (Paspalum vaginatum Swartz) as a recreational turf has increased in recent years. On similar species, such as bermudagrass (Cynodon ssp.), plant growth regulators (PGRs) are used to decrease mowing frequency. However, no data currently exists for the use of PGRs on seashore paspalum. Therefore, field experiments were conducted over 2 years to determine the effects of trinexapac-ethyl and paclobutrazol on seashore paspalum. Paclobutrazol was non-injurious to turf when applied sequentially, 4 weeks apart, at rates as high as 0.56 kg·ha-1 of a.i. However, these same treatments failed to reduce vegetative growth. Conversely, trinexapac-ethyl treatments produced unacceptable injury (>15%) when applied sequentially, 4 weeks apart, at rates higher than 0.19 kg·ha-1 of a.i. As trinexapac-ethyl rates were reduced to ≤0.14 kg·ha-1 of a.i., injury was reduced to ≤ 12% while vegetative growth was suppressed to ≥59%, relative to nontreated seashore paspalum. Therefore, trinexapac-ethyl can serve as an effective option for those managing seashore paspalum turf areas. Chemical names used: 4-(Cyclopropyl-α-hydroxymethylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); (+/-)-R *,R *-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazol-1-ethanol (paclobutrazol).

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S.K. Braman, R.R. Duncan, W.W. Hanna and W.G. Hudson

Bermudagrass (Cynodon sp.) and paspalum (Paspalum vaginatum) genotypes were evaluated in laboratory, greenhouse, and field experiments for potential resistance to the common turfgrass pests, tawny mole cricket (Scapteriscus vicinus Scudder) and southern mole cricket (Scapteriscus borellii Giglio-tos). Potential resistance among 21 seashore paspalums to both insects in an environmental chamber at 27 °C, 85% relative humidity, and 15 hours light/9 hours dark) revealed that Glenn Oaks `Adalayd' was least tolerant of cricket injury, while 561-79, HI-1, and `Excalibur' were most tolerant. Nymphal survival was not influenced by turfgrass type. Plant selections that maintained the highest percentage of their normal growth after 4 weeks of feeding by tawny mole crickets over three separate greenhouse trials were 561-79, HI-1, HI-2, PI-509018, `Excalibur', SIPV-1 paspalums, and `Tifeagle' and `Tifsport' bermudagrasses. Although none of the tested genotypes was highly resistant to tawny mole cricket injury, `TifSport' bermudagrass and 561-79 (Argentine) seashore paspalum were most tolerant.

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T.J.K. Radovich*, R.C. Pratt, L.A. Duncan, N. Welty and M.D. Kleinhenz

Cucurbita maxima and C. pepo are difficult to hybridize, and it was our objective to generate F1 hybrids between ornamental cultivars of the two species. C. maxima `Lakota' and C. pepo `Jack O'Lantern'; and `OZ'; were selected as parents. `Lakota' (L) is an heirloom, hubbard-type cultivar producing pear-shaped, red-orange fruit with dark green mottling, `Jack O'Lantern'; (J) is an open-pollinated Halloween-type pumpkin cultivar and `OZ' is a Halloween-type hybrid. Sixteen plants of each cultivar were greenhouse-grown in a CRB design during the period July-Sept. 2003. Interspecific crosses were made in both directions, with intraspecific crosses (J × O) and selfs (L) serving as controls. Fruits were harvested about 20 d after pollination. Embryos were excised under aseptic conditions and grown on either full strength Murashige and Skoog (MS) media with 6% sucrose (S6), full strength MS media with 6% maltose (M6), or half strength MS media with 3% sucrose (S3). Fruit set was generally greater in the intraspecific crosses (33%) and selfs (67%) than in the interspecific crosses (15 %), with the notable exception of the interspecific combination L × J (85% fruit set). Embryos of interspecific and control crosses were about 1.5mm and >1cm long, respectively. Hypocotyl and root growth 10 d after plating was better on S3 (3.2 and 1.7 cm) than on S6 (1.6 and 0.25 cm) or M6 (0.35 and 0 cm), and a greater number of functional hybrids were obtained from embryos grown on S3 (6 plants) than on S6 (2 plants) or M6 (2 plants). The interspecific plants were backcrossed to one of the parents and novel combinations of shape, color and variegation in hybrid fruit were observed.