Daily air temperature (°F) and rainfall (inch) from 28 Jul to 13 Oct 2020.
Daily air temperature (°F) and rainfall (inch) from 2 Jul to 29 Sep 2021.
Normalized difference vegetation index (A) and leaf area index (B) as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and year (2020 and 2021) evaluated 60 d after seeding. The uppercase letters indicate significant differences between cultivars within the same year at P ≤ 0.05. The lowercase letters indicate significant differences between years within the same cultivar at P ≤ 0.05.
Normalized difference vegetation index (A) and leaf area index (B) as affected by plant growth-promoting microorganisms (PGPMs) and year (2020 and 2021) evaluated 60 d after seeding. The uppercase letters indicate significant differences among PGPM treatments within the same year at P ≤ 0.05. The lowercase letters indicate significant differences between years within the same PGPMs at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient (a.i.)/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Leaf area index as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and plant growth-promoting microorganisms (PGPMs) evaluated at 60 d after seeding. The uppercase letters indicate significant differences among PGPMs within the same cultivar at P ≤ 0.05. The lowercase letters indicate significant differences between cultivars within the same PGPM at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Leaf area index as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and plant growth-promoting microorganisms (PGPMs) evaluated at 90 d after seeding. The uppercase letters indicate significant differences among PGPMs within the same cultivar at P ≤ 0.05. The lowercase letters indicate significant differences between cultivars within the same PGPM at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient (a.i.)/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
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Slow seed germination and seedling growth cause the slow field establishment of kentucky bluegrass (Poa pratensis). Previous research showed that plant growth-promoting microorganisms (PGPMs) can enhance plant growth and stress tolerance. The objective of this research was to determine the effect of six commercial PGPM products on promoting kentucky bluegrass establishment in the field. Two kentucky bluegrass cultivars Kenblue (stress-sensitive) and Moonlight (stress-tolerant) were seeded at 3 lb pure live seed/1000 ft2 in Jul 2020 and 2021. Six PGPMs, Beauveria bassiana (strain GHA), Bacillus subtilis (strain GB03), Azadirachtin, Bacillus firmus (strain1-582), Trichoderma harizanum Rifai (strain T-22) combined with T. virens (strain G-41), and Bacillus subtilis (strain QST713), were applied in the field at seeding and every 10 days thereafter. The normalized difference vegetation index (NDVI) and leaf area index (LAI) were measured at 30, 60, and 90 days after seeding. The results showed that all six PGPMs had a similar or higher NDVI and LAI compared to those of the control (i.e., tap water), with the best results seen in B. bassiana (strain GHA) [colony-forming unit (cfu)/acre = 4.8 × 1013], T. harzianum Rifai (strain T-22) (3.4 × 109 cfu/acre) + T. virens (strain G-41) (7.2 × 108 cfu/acre), and B. subtilis (strain GB03) (1.1 × 1011 cfu/acre). The efficacy of PGPMs may be enhanced when stress-tolerant plants are used and/or under cool summer conditions. Our results suggest that PGPMs have the potential to accelerate kentucky bluegrass establishment in the field.
Kentucky bluegrass is a common cool-season turfgrass for golf courses, recreational areas, and home lawns in the northern region and the turfgrass transition zone of the United States (Huff 2003). Kentucky bluegrass has dense leaves, smooth and upright stems, and vigorous rhizomes (Christians 2011); however, it is slow in germination and initial growth. Kentucky bluegrass needs 115.6 degree-days (DDs) to reach 50% germination [base temperature (Tb) = 36.7 °F] compared with 63.9 DDs for perennial ryegrass (Lolium perenne) (Tb = 38.5 °F) and 43.8 DDs for red fescue (Festuca rubra ssp. littoralis) (Tb = 36.7 °F) (Larsen and Bibby, 2005). Braun et al. (2023) reported that the days to reach 50% germination of eight turfgrass species increased in the following order: perennial ryegrass (5.1), strong creeping red fescue (F. rubra spp. rubra; 6.4), slender creeping red fescue (6.7), hard fescue (F. brevipila; 6.8), chewings fescue (F. rubra ssp. commutate; 7.1), sheep fescue (F. ovina; 7.5), tall fescue (Schedonorus arundinaceus; 7.9), and kentucky bluegrass (9.2). The slow germination of kentucky bluegrass results in a high risk of weed invasion and domination by other species when used in a mixture during the establishment.
Previous research showed that plant growth-promoting microorganisms (PGPMs), including arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria (PGPB), can improve seed germination and field performance of many plant species. Gholami et al. (2009) evaluated the effects of six plant growth-promoting rhizobacteria (PGPRs) (Pseudomonas putida strain R-168, P. fluorescens strain R-93, P. fluorescens DSM 50090, P. putida DSM291, Azospirillum lipoferum DSM 1691, and A. brasilense DSM 1690) on seed germination, seedling growth, and yield of maize (Zea mays). The results showed that four PGPRs (P. putida strain R-168, P. fluorescens strain R-93, P. fluorescens DSM 50090, and A. brasilense DSM 1690) increased seed germination and seedling growth, and that all six PGPBs improved yield. Fatemeh et al. (2014) reported a higher final germination rate, faster germination speed, and lower mean germination time in the PGPM-treated Crataegus sp. seeds than those of the nontreated ones. Seed germination is promoted by PGPMs, which can help break down cellulose or hemicelluloses in the cell wall and soften the seedcoat (Fatemeh et al. 2014). Additionally, PGPMs can enhance the acquisition of water and nutrients, modulate plant hormone levels, regulate source-sink relations, energize the metabolism and synthesis of antibiotics, and improve systemic resistance in plants (Glick 2012).
Because microorganisms have multiple functions in influencing plant growth and development (Glick 2012), commercial PGPM products may be used for more than one purpose. For instance, Zhang and Rue (2024) reported that kentucky bluegrass treated with Beauveria bassiana (strain GHA) (biological insecticide) and Bacillus subtilis (strain GB03) (biological fungicide) showed similar or better growth under drought and saline conditions compared with that of the untreated ones. The objective of this research was to determine if the commercial PGPM products, which are registered for turf disease and insect control, can promote kentucky bluegrass establishment in the field.
This field experiment was conducted at the North Dakota State University Turfgrass Research Center (Fargo, ND, USA). Soil was Fargo clay (Fargo series, fine, smectitic, frigid Typic Epiaquerts) with pH of 6.7, 4.4 ppm NO3-N, 36 ppm phosphorus (P), and 645 ppm potassium (K). N-(phosphonomethyl) glycine (Glyphosate Plus, Control Solutions Inc., Pasadena, TX, USA) was sprayed in a kentucky bluegrass field plot on 6 Jul 2020 at 4 lb active ingredient (a.i.)/67 gal water/acre using a backpack sprayer. The plot was then rototilled to a depth of 3 inches and smoothed over with a heavy metal drag 1 week later. ‘Kenblue’ and ‘Moonlight’ kentucky bluegrass were seeded at 3 lb pure live seeds/1000 ft2 on 28 Jul 2020. A starter fertilizer (18–24–5) was applied at 1 lb P2O5/1000 ft2 at the seeding time. Light irrigation was applied seven times per day for 3 min each time through overhead irrigation during the first 2 weeks after seeding. Irrigation was then reduced to once daily or adjusted according to the environmental conditions to maintain adequate soil moisture. Six commercially available PGPM products were included in this experiment (Table 1). All PGPM products were applied at seeding and approximately 10-d intervals afterward, except Bacillus firmus (strain 1-582) (5 d before seeding and once per month thereafter) and Trichoderma harzianum Rifai (strain T-22) + T. virens (strain G-41) (at seeding and once per month thereafter) according to the suggested highest application frequency on the label. A no-PGPM treatment (i.e., tap water applied at seeding and 10-d intervals thereafter) was included as the control. All PGPM treatments, including the control, were applied with a CO2-pressurized sprayer in water equivalent to 230 gallon/acre. Mowing started 3 to 4 weeks after seeding with a walk-behind rotary mower (Toro Recycler; The Toro Company, Bloomington, MN, USA) at 1.5 inches and gradually reduced to 0.75 inches in 2 weeks. A Toro lightweight out-front rider (Toro Groundsmaster 7200; The Toro Company) was used thereafter at the same mowing height, 0.75 inches, until 13 Oct 2020. Clippings were collected and removed from the research area. Weeds were handpicked once per week starting 3 weeks after seeding and until the end of the experiment (i.e., 13 Oct 2020). The experiment was repeated from 2 Jul to 5 Oct 2021 in a new area that was 50 ft away from the research plot used in 2020. It was also a Fargo clay with pH of 7.2, 2.3 ppm NO3-N, 39 ppm P, and 545 ppm K. Management practices were identical in both years. A weather station was located approximately 45 ft away from the research plot to record precipitation and air temperature (Figs. 1 and 2).
Citation: HortTechnology 35, 1; 10.21273/HORTTECH05542-24
Citation: HortTechnology 35, 1; 10.21273/HORTTECH05542-24
The experiment was set-up as a split-plot design, with the whole-plot being cultivar-arranged in a randomized complete block design with four replicates and the sub-plot (5 × 5 ft) being the PGPM treatment. Turf coverage has been traditionally rated using a visual system, which is subjective to the evaluator’s judgment (Richardson et al. 2001). Therefore, turf coverage was quantified using a hand-held multispectral radiometer (model MSR16; CropScan, Inc., Rochester, MN, USA) at 30, 60, and 90 d after seeding (DAS). Reflectance was determined based on wavelengths centered at 450, 660, 710, 760, 810, 900, 950, 1200, 1480, and 1650 nm. The normalized difference vegetation index [NDVI = (R760 − R710)/(R760 + R710)] and leaf area index (LAI = R950/R660) were calculated because previous research has shown that the NDVI and LAI are closely correlated with color, density, and percent live cover of turf canopy (Bell et al. 2002; Bremer et al. 2011; Jiang and Carrow 2007). Canopy reflectance was taken between 1100 and 1300 HR central standard time on days with no cloud cover and the sensor held at 1.5 m aboveground level. If weather did not permit measurements, then measurements were taken the following day. Data were subjected to an analysis of variance using PROC GLIMMIX (SAS version 9.4; SAS Institute Inc., Cary, NC, USA). Least squares means were separated using the pdiff option at P = 0.05.
At 30 DAS, ‘Kenblue’ and ‘Moonlight’ had similar NDVI and LAI in both years when data were pooled across PGPM and year (Table 2). Similarly, no significant differences in the NDVI and LAI were observed among the PGPM products. In contrast, plants seeded in 2021 had higher NDVI and LAI than those of plants seeded in 2020. No treatment interactions were detected at 30 DAS.
At 60 DAS, year, cultivar, and PGPM products interactively influenced the NDVI and LAI (Table 2). ‘Moonlight’ outperformed ‘Kenblue’ in both years, except for LAI in 2020 (Fig. 3). ‘Kenblue’ had higher NDVI and LAI in 2020 than those in 2021, whereas ‘Moonlight’ performed similarly in both years. The averaged NDVI of Beauveria bassiana (strain GHA), Trichoderma harzianum Rifai (strain T-22) + T. virens (strain G-41), Bacillus subtilis (strain GB03), and Azadirachtin was 0.51 in 2020, which was 13.9% higher than that of the control (Fig. 4). The LAI of turfgrass treated with B. bassiana (strain GHA) and Azadirachtin was 12.07, which was higher than the average value (9.02) of B. subtilis (strain QST713), B. firmus (strain 1-582), and the control. In 2021, however, Azadirachtin-treated turfgrass showed consistently lower NDVI and LAI than those of other PGPM treatments. Comparing the results of 2020 to 2021, turf under the T. harzianum (strain T-22) + T. virens (strain G-41), Azadirachtin, and B. subtilis (strain GB03) (LAI only) treatments performed better in 2020 than in 2021. When the interaction of cultivar × PGPM was detected in the LAI at 60 DAS (Table 2), ‘Kenblue’ treated with T. harzianum + T. virens performed better than other PGPM treatments (Fig. 5). In ‘Moonlight’, B. bassiana (strain GHA) and B. subtilis (strain GB03) treatments had higher LAI than that of B. firmus (strain 1-582), Azadirachtin treatments, and the control. ‘Kenblue’ treated with B. subtilis (strain QST713), B. bassiana (strain GHA), and B. subtilis (strain GB03) had lower LAI than that of ‘Moonlight’, while no cultivar differences in the LAI were observed in other PGPM treatments.
Citation: HortTechnology 35, 1; 10.21273/HORTTECH05542-24
Citation: HortTechnology 35, 1; 10.21273/HORTTECH05542-24
Citation: HortTechnology 35, 1; 10.21273/HORTTECH05542-24
At 90 DAS, no two-way or three-way interactions were detected in NDVI (Table 2). ‘Moonlight’ had a better NDVI than that of ‘Kenblue’ when data were pooled across PGPM treatment and year. Turfgrass also had a higher NDVI in 2020 compared to that in 2021. No differences in NDVI were observed among the PGPM treatments. Similarly, the LAI was higher in 2020 compared to that in 2021 (Table 2). However, the cultivar × PGPM interaction was detected in LAI at 90 DAS. ‘Moonlight’ showed a higher LAI than that of ‘Kenblue’ in all PGPM treatments, Differences in LAI between the two cultivars ranged from 4.7% with Azadirachtin treatment to 40.5% with B. bassiana (strain GHA) treatment (Fig. 6). In ‘Kenblue’, Azadirachtin treatment had the highest LAI, which was 17.4% higher than the average (9.31) of B. bassiana (strain GHA), B. subtilis (strain GB03), and B. firmus (strain 1-852). In contrast, B. bassiana (strain GHA) treatment showed the highest LAI for ‘Moonlight’, whereas Azadirachtin was among the four PGPM treatments that resulted in low LAI (Fig. 6).
Citation: HortTechnology 35, 1; 10.21273/HORTTECH05542-24
The Association of Official Seed Analyst suggested that a 59/77 °F (night/day) temperature regime should be used to test kentucky bluegrass seed germination (Association of Official Seed Analysts 2016). However, research has shown that kentucky bluegrass can germinate well at much higher temperatures. Van’T Klooster (2007) evaluated kentucky bluegrass germination on a temperature gradient plate (41 to 95 °F) and the results showed that the optimal germination temperatures ranged from 70 to 91 °F, depending on the cultivar. Similarly, Giolo et al. (2017) reported that the kentucky bluegrass seed germination rate and speed were similar or slightly increased as the temperature increased from 68/86 °F to 79/97 °F (night/day) before a significant decrease at 84/102 °F, and limited germination was observed at 90/108 °F. In this study, the averaged air minimum/maximum temperatures by 30 DAS were 61/81 °F and 64/86 °F in 2020 and 2021, respectively, which should not interfere with the kentucky bluegrass germination (≤30 DAS) (Figs. 1 and 2). The high temperature in 2021 might help fulfill the high thermal requirement of kentucky bluegrass, resulting in higher NDVI and LAI observed at 30 DAS in 2021 than those in 2020 (Table 2). Our previous research showed a high growth rate of ‘Kenblue’ at the seed germination and seedling growth stage (≤30 DAS) under the controlled environment (Yang and Zhang 2019; Zhang and Rue 2024); however, these previous findings did not translate into the field observations in this study. One possibility is that turfgrass was quantified as tissue biomass under the controlled environment, while the surface coverage was evaluated in the current field study.
Fry and Huang (2004) reported that the optimal temperatures for shoot growth of cool-season turfgrass, such as kentucky bluegrass, were 64 to 75 °F, and temperatures out of this range negatively affect turf growth and performance. In this study, the average air maximum and minimum temperatures from 31 to 90 DAS were 80 and 57 °F in 2021 and 71 and 49 °F in 2020, respectively. Furthermore, there were 44 d (including 14 d above 86 °F) and 22 d (including 3 d above 86 °F) with a maximum air temperature above 75 °F from 31 to 90 DAS in 2021 and 2020, respectively (Figs. 1 and 2). Although no leaf wilting was visually observed, the higher air temperatures in 2021 from 31 to 90 DAS compared with those in 2020 might have inhibited turfgrass growth and development, resulting in lower NDVI and LAI at 60 and 90 DAS (Table 2, Figs. 3 and 4). Compared with ‘Moonlight’, ‘Kenblue’ is more sensitive to heat, drought, and salt (Lewis et al. 2012; Li et al. 2014; Qian 2003; Yang and Zhang 2019; Zhang and Rue 2024), which may contribute to the lower NDVI and/or LAI at 60 and 90 DAS observed in this study (Table 2, Figs. 3, 5, and 6).
Because the short shelf life of PGPMs is a limiting factor for their commercial use, consumers are interested in identifying their other potential use in addition to what they are registered for (mostly biological fungicides or biological insecticides). In the current study, six commercially available PGPMs were evaluated to determine their efficacy for improving kentucky bluegrass field establishment. Our results showed no effect on promoting seed germination and early seedling growth among the PGPM treatments at 30 DAS (Table 2), which might be attributable to time requirements for the bioagents to colonize in the soil and plants. However, all PGPM treatments showed similar or better results compared with those of the control when evaluated at 60 and 90 DAS in both years, except Azadirachtin (Table 2, Figs. 4–6), thus providing evidence that these PGPM products could be effective for improving kentucky bluegrass field establishment after they successfully colonized the soil and plants. Three PGPM treatments, T. harzianum + T. virens, B. subtilis (strain GB03), and Azadirachtin, showed a lower NDVI and/or LAI in 2021 than those in 2020, particularly in the treatment of Azadirachtin (Fig. 4). It is possible that these biostimulants are more effective under low temperatures. For example, the application of Azadirachtin is recommended at temperatures above 70 °F (Ring 2019), but application at temperatures above 90 °F should be avoided (United States Environmental Protection Agency 2012). The results also showed that these PGPM products were better for promoting the growth of ‘Moonlight’ than for promoting that of ‘Kenblue’ (Figs. 5 and 6). Long-term field studies are needed to further evaluate the efficacy of PGPM products for turfgrass establishment and performance.
Slow field establishment is one of the factors that limits the use of kentucky bluegrass. The six commercially available PGPM products evaluated in the present study showed promise for improving kentucky bluegrass field establishment, especially in the treatments of B. bassiana (strain GHA) (4.8 × 1013 cfu/acre), T.harzianum Rifai (strain T-22) (3.4 × 109 cfu/acre) + T. virens (strain G-41) (7.2 × 108 cfu/acre), and B. subtilis (strain GB03) (1.1 × 1011 cfu/acre). The stress tolerance of turfgrasses and the applying conditions, such as temperature, may affect the efficacy of PGPMs.
Daily air temperature (°F) and rainfall (inch) from 28 Jul to 13 Oct 2020.
Daily air temperature (°F) and rainfall (inch) from 2 Jul to 29 Sep 2021.
Normalized difference vegetation index (A) and leaf area index (B) as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and year (2020 and 2021) evaluated 60 d after seeding. The uppercase letters indicate significant differences between cultivars within the same year at P ≤ 0.05. The lowercase letters indicate significant differences between years within the same cultivar at P ≤ 0.05.
Normalized difference vegetation index (A) and leaf area index (B) as affected by plant growth-promoting microorganisms (PGPMs) and year (2020 and 2021) evaluated 60 d after seeding. The uppercase letters indicate significant differences among PGPM treatments within the same year at P ≤ 0.05. The lowercase letters indicate significant differences between years within the same PGPMs at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient (a.i.)/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Leaf area index as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and plant growth-promoting microorganisms (PGPMs) evaluated at 60 d after seeding. The uppercase letters indicate significant differences among PGPMs within the same cultivar at P ≤ 0.05. The lowercase letters indicate significant differences between cultivars within the same PGPM at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Leaf area index as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and plant growth-promoting microorganisms (PGPMs) evaluated at 90 d after seeding. The uppercase letters indicate significant differences among PGPMs within the same cultivar at P ≤ 0.05. The lowercase letters indicate significant differences between cultivars within the same PGPM at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient (a.i.)/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Contributor Notes
We thank United States Golf Association and ND Hatch Project (ND01509) for funding this project.
Q.Z. is the corresponding author. E-mail: qi.zhang.1@ndsu.edu.
Daily air temperature (°F) and rainfall (inch) from 28 Jul to 13 Oct 2020.
Daily air temperature (°F) and rainfall (inch) from 2 Jul to 29 Sep 2021.
Normalized difference vegetation index (A) and leaf area index (B) as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and year (2020 and 2021) evaluated 60 d after seeding. The uppercase letters indicate significant differences between cultivars within the same year at P ≤ 0.05. The lowercase letters indicate significant differences between years within the same cultivar at P ≤ 0.05.
Normalized difference vegetation index (A) and leaf area index (B) as affected by plant growth-promoting microorganisms (PGPMs) and year (2020 and 2021) evaluated 60 d after seeding. The uppercase letters indicate significant differences among PGPM treatments within the same year at P ≤ 0.05. The lowercase letters indicate significant differences between years within the same PGPMs at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient (a.i.)/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Leaf area index as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and plant growth-promoting microorganisms (PGPMs) evaluated at 60 d after seeding. The uppercase letters indicate significant differences among PGPMs within the same cultivar at P ≤ 0.05. The lowercase letters indicate significant differences between cultivars within the same PGPM at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
Leaf area index as affected by kentucky bluegrass cultivar (Kenblue and Moonlight) and plant growth-promoting microorganisms (PGPMs) evaluated at 90 d after seeding. The uppercase letters indicate significant differences among PGPMs within the same cultivar at P ≤ 0.05. The lowercase letters indicate significant differences between cultivars within the same PGPM at P ≤ 0.05. PGPM treatments: control (i.e., tap water); 4.8 × 1013 colony-forming units (cfu)/acre of Beauveria bassiana (strain GHA) (BotaniGard 22WP; BioWorks, Inc., Butte, MT, USA); 1.1 × 1011 cfu/acre of Bacillus subtilis (strain GB03) (Companion; Growth Products Ltd., White Plains, NY, USA); 0.02 lb active ingredient (a.i.)/acre of Azadirachtin (Molt-X; BioWorks, Inc., Victor, NY, USA); 2.7 × 1012 cfu/acre of Bacillus firmus strain 1-582 (Nortica 10WP; Bayer Experimental Science, Research Triangle Park, NC, USA); 3.4 × 109 cfu/acre Trichoderma harzianum Rifai strain T-22 + 7.2 × 108 cfu/acre of T. virens strain G-41 (RootShield PLUS+ WP; BioWorks, Inc., Victor, NY, USA); and 1 × 1012 cfu/acre of Bacillus subtilis strain QST713 (Serenade; Bayer CropScience LP, Research Triangle Park, NC, USA).
