Trygve S. Aamlid’s research while affiliated with Norwegian Institute of Bioeconomy Research and other places

Red fescue (RF, Festuca rubra L.) is one of the most widely used turfgrass species in Europe. The subspecies Chewings fescue (CF) and slender creeping red fescue (SlCRF) are used on putting greens because they tolerate a mowing height of 4–5 mm. Previous research has shown CF to be more winter‐hardy than SlCRF, however, SlCRF has a greener winter color. Our objective was to find the optimal weight ratio of the two subspecies in seed blends for greens in contrasting climatic regions of the Nordic countries. Musica and Cezanne (reference varieties in SCANGREEN variety testing since 2012) were selected as representatives for CF and SlCRF, respectively. Seed blends including CF/SlCRF in weight ratios of 75/25, 50/50, and 25/75 were compared to pure CF and SlCRF at Sydsjælland GC, Denmark, NIBIO Landvik, Norway, NIBIO Apelsvoll, Norway, and Reykjavik GC, Iceland as an add‐on to SCANGREEN variety testing 2015–2018. Results showed the optimal blends to produce higher turfgrass quality and tiller density than monocultures of either subspecies at all sites except Apelsvoll where plots were killed during the first winter. The best‐performing CF/SlCRF blend was 50/50 at Sydsjælland and Landvik and 75/25 at Reykjavik. While this shows seed blends to have advantages compared with the pure subspecies, the study should be repeated with a focus on dollar spot ( Clarireedia spp.), which has become a major turfgrass disease in Southern Scandinavia since these trials were conducted.

The primary benefits of turfgrass sod include rapid greenery and soil coverage, but its production causes concerns about soil losses at production sites. Soil adheres to the grass root system during harvesting and is removed from the sod farm, which in the long run might lead to soil degradation on the sod farm. In this study, we investigated sod thickness and the removal of organic and mineral matter when harvesting 24 fields representing 12 Norwegian sod farms in 2022 and 2023. On each field, 10 sod strips were randomly chosen, and five sod plugs were collected from each strip. Sod thickness was measured using a sliding gauge. Sod mineral matter (SMM: soil and thatch mineral matter) and sod organic matter (SOM: soil and thatch organic matter) contents were quantified by loss on ignition at 550°C. Management and field properties were also documented. Results showed an average amount of mineral matter in the sod strips of 36 Mg ha ⁻¹ for all fields but with significant variation among fields ( p < 0.001). The average SOM content was 10 Mg ha ⁻¹ . Mean sod thickness was 15.4 mm and had a strong correlation with SOM ( r = 0.8) but only a moderate correlation with SMM ( r = 0.6). Soil water content and surface hardness at harvest affected sod thickness and SMM only slightly. Sod harvesters with twin heads harvested significantly thicker sod strips and removed more mineral matter than harvesters with single cutting heads. Soil texture did not have a significant impact on sod thickness or mineral matter removal.

Ice encasement (IE) is one of the big challenges in winter stress management on golf course putting greens in Northern Scandinavia. The turfgrass is damaged due to lack of oxygen (hypoxia or anoxia) and accumulation of toxic by‐products of anaerobic respiration. Breeding IE‐tolerant turfgrass species and varieties is the best defense against these challenges. A method to simulate ice encasement was tested to screen selected varieties of winter‐hardy bentgrass species and red fescue subspecies. Note that 32 varieties were chosen from the SCANGREEN trial seeded at NIBIO Landvik, Norway, in 2019. Samples were taken in December 2020, 2021, and 2022, vacuum sealed in plastic, and stored in darkness at 0.5°C for up to 77 days to test them for their tolerance to simulated ice encasement (SIE). Samples were incubated at different intervals; plants were potted, and tiller survival was tested after 4 weeks of regrowth. Lethal duration of ice encasement (LD 50 ) that is, the number of days under anoxia that kills 50% of the plant population for each species and variety was calculated. The results showed that the ranking of cool season turfgrass species for tolerance to SIE was velvet bentgrass > Chewings fescue > slender creeping red fescue = colonial bentgrass > creeping bentgrass. This ranking does not fully reflect the ranking found in field tests where velvet bentgrass was superior together with creeping bentgrass. SIE caused a more rapid development of anoxia than IE in the field, and we hypothesize that creeping bentgrass is less tolerant to these conditions compared to the other species tested. To make the SIE method more representative for IE in field, it should be further adapted with incubation at lower temperatures, and with acclimation conditions to be standardized prior to sampling. Within species, the best tolerance to IE was found in velvet bentgrass Nordlys, creeping bentgrass Penncross, Chewings fescue Lykke, and slender creeping red fescue Cezanne.

Ice encasement is a major concern for turfgrass managers in cold climates; however, there is a lack of data about both which turfgrasses are best suited for survival under these conditions and the reasons behind the superior recovery of some grasses from long‐term ice encasement. In this study, we encased golf course putting greens‐height field plots of creeping bentgrass (Agrostis stolonifera L.), velvet bentgrass (Agrostis canina L.), annual bluegrass (Poa annua L. var. reptans Hausskn.), Chewings fescue (Festuca. rubra L. ssp. commutata Gaudin), and slender creeping red fescue (F. rubra L. ssp. littoralis (G. Mey.) Auquier) with ice for 90–120 days with the inclusion of CO2, O2, and temperature sensors at 2.5 and 12.5 cm depth to better understand environmental conditions under ice and factors related to winterkill. Velvet bentgrass had the best overall performance and recovery, while annual bluegrass did not survive. Differences in recovery among turfgrass taxa may have been affected by the length of the ice encasement period, higher CO2 levels (>40,000 ppm), and lower O2 values, particularly in the second experimental run. During the recovery period in both years, photochemical efficiency values began increasing 5–10 days before percent green cover, suggesting that visual performance of the turf surface is a lagging indicator of recovery. Overall, recovery from ice encasement was annual bluegrass < Chewings fescue < creeping bentgrass = slender creeping red fescue = velvet bentgrass. These results can guide turfgrass managers in making species selection decisions in areas where long‐duration ice encasement is a risk.

Winter damage of golf turf in northern environments is a persistent challenge, and reseeding is often necessary to promote recovery and to maintain adequate density and uniformity for play. However, adverse conditions associated with spring seedings can negatively impact reestablishment of creeping bentgrass ( Agrostis stolonifera L.) (CBG) on golf greens, tees, and fairways. The objectives of the research were to examine different strategies to promote rapid reestablishment of CBG in early spring, including cultivar selection, use of a synthetic cover, and application of plant health products. To assess the impacts of CBG cultivars and cover on reestablishment, 12 cultivars and two cover treatments (without or with a permeable synthetic cover) were established at two locations in 2021 (South Deerfield, A, and Saint Paul, MN). The effects of plant health products on CBG establishment were assessed in separate field trials at two locations in 2021 and 2022 (South Deerfield, MA, and Grimstad, Norway). Plant health product treatments were applied on a weekly basis following emergence and included: control (water), chitosan, silica, acibenzolar S‐methyl, glycine betaine, seaweed extracts (alone or together with humic substances), trinexapac‐ethyl, and gibberellic acid. Soil and air temperatures were monitored, and plots were visually assessed for changes in percent green turfgrass cover. The use of a permeable cover increased soil temperatures and decreased the time to achieve 50% turfgrass cover by 7–12 days, depending on location and regardless of cultivar. Compared to effect of covering treatment, most CBG did not significantly vary in spring establishment rates, except for Independence, which exhibited slower establishment. Among the various plant health products tested over 2 years and two locations, we did not identify any specific product that consistently enhanced early spring establishment of CBG.

Turfgrass winter kill due to freeze/thaw cycles and ice encasement (IE) is a problem on putting greens the Nordic countries. Our objectives were (1) to investigate how green coverage with impermeable plastic before IE affects soil temperature, O 2 and CO 2 concentrations, winter survival and spring recovery of creeping bentgrass (CRB), red fescue (RF), and annual bluegrass (AB) and (2) to explore how these turfgrasses are affected by snow and ice removal during the entire winter or parts of it. Six treatments were imposed on 5‐month‐old turf of the three species during the winters 2020/2021 and 2021/2022 at NIBIO Apelsvoll, Norway (60°42′ N). With an average soil temperature at 2‐cm depth of −0.9°C and the lowest O 2 concentrations around 5%, conditions under IE or plastic + IE treatments never became anoxic. On average for six treatments and 2 years, CRB and RF had significantly better winter survival (both 52%) than AB (25%). Turfgrass winter survival, spring color, and spring growth were significantly better (62% survival on average for species) with plastic between the grass and 10‐cm IE than with 10‐cm IE directly on the grass (23% survival). Snow and ice removal throughout the winter or before IE in early January improved turfgrass freezing tolerance in January but did not improve winter survival, green color, or spring growth compared with the control treatment with natural winter conditions. We conclude that putting greens in areas with unstable winters and risk for prolonged IE ought to be protected by impermeable plastic. Ventilation under the plastic may be necessary on old greens with more organic matter than in this experiment. On frozen uncovered greens, it is better to avoid prolonged IE by snow removal before rain or warm spell in December/early January than by mechanical ice removal in March.

Red fescue ( Festuca rubra L.) is the preferred turfgrass species for low‐input golf course putting greens in Northern Europe. While it is well recognized that fescue requires less fertilizer than bentgrasses ( Agrostis spp.) or annual bluegrass ( Poa annua L.), the optimal fertilizer distribution throughout the growing season has not been investigated. Our objective was to determine the effects of three seasonal fertilizer distributions on turfgrass quality, seasonal growth rates, root development, and competition from annual bluegrass on a sand‐based red fescue putting green at the NIBIO (Norwegian Institute of Bioeconomy Research) Turfgrass Research Center, Landvik, Norway (58° N). All fertilizer treatments comprised weekly inputs of a complete, liquid fertilizer solution for a total of 11 g N m ⁻² year ⁻¹ , but the inputs were distributed with (1) the highest weekly rates from early May to mid‐summer (SPRING+), (2) equal weekly rate from early May through late September (FLAT), or (3) the highest weekly rates from mid‐August to late September (FALL+). SPRING+ fertilization resulted in higher turfgrass quality, deeper roots, and, in the second experimental year, less annual bluegrass than FALL+ fertilization. The advantage of FALL+ fertilization was faster green‐up and enhanced growth in September, October, and April, but this came at the expense of more annual bluegrass. Results are discussed in light of previously published data on temperature and fertilizer requirements for the growth of red fescue versus annual bluegrass.

On European golf courses, small lightweight robotic mowers have recently been introduced for fairway and rough mowing. In this study, turfgrass quality and the coverage of broadleaf weeds in three cool‐season grasses were compared in response to robotic and traditional fairway mowing. Experiments with pure swards of red fescue ( Festuca rubra L.), colonial bentgrass ( Agrostis capillaris L.), and Kentucky bluegrass ( Poa pratensis L.) were carried out at NIBIO Landvik, Norway, to evaluate differences between lightweight robotic mowing and reel mowing. In a mixture of the three species turfgrass quality and the coverage of broadleaf weeds were compared in response to robotic and reel mowing at yearly fertilizer levels from 0 to 120 kg N ha ⁻¹ . The results showed that both robotic and reel mowing were found to provide high turfgrass quality, while lower coverage of broadleaf weeds (predominantly white clover [ Trifolium repens L.]) was found with robotic mowing independent of grass species. In the mixed stand, higher turfgrass quality was found with robotic mowing regardless of N rate, but N rates above 60 kg ha ⁻¹ year ⁻¹ were necessary to keep the coverage of white clover in fall on an acceptable low level. Our results suggest that robotic mowing can decrease the spread of white clover at a fairway mowing height of 15 mm, but more research is needed to clarify at which mowing heights, mowing frequencies, and fertilizer levels we can get the best competitiveness against broadleaf weeds on fairways with robotic mowing.

In the Nordic countries, ice encasement of golf greens and agricultural grass fields under sunlight heat often leads to grass death due to oxygen depletion and accumulation of carbon dioxide and metabolites from anaerobic respiration under the ice layer. The phenomenon is termed 'isbrann' in Norwegian and it is a severe type of winter damage that may also affect germination and growth after reseeding. We have employed soil water metabolome analyses to differentiate and identify small, water-soluble metabolites produced in ice-encased grass for a better understanding of how ice and anoxic soils might affect grass plants. We employed a next-generation plant-metabolomics workflow to differentiate and identify metabolites related to ice-encased, anoxic soils in golf greens. Various organic acids and amino acids were upregulated or downregulated in water extracted from the thatch/rhizosphere soil layer, which could be related to root exudation and early stress responses in plants. Adenine for example, might have a role in promoting plant growth and recruiting beneficial microbial communities in the root zones. But some of these metabolites may also be produced by microorganisms. Butyric acid and acetic acid, which are produced by anaerobic microorganisms, were to our surprise detected at comparable levels in both ice-encased and control samples. The work forms a basis towards a better understanding of how the grass plants reacts to anoxic stress and the interplay between soil microorganisms and plant roots in an anoxic environment. Most of the grass (87%) in the ice-encased plots died due to the anoxic damage. However, the grass could be reestablished with new seeds and the concentrations of metabolites resulting from anoxia was not high enough to inhibit later germination and seedling growth.

This study quantifies golf course pesticide risk in five regions across the US (Florida, East Texas, Northwest, Midwest, and Northeast) and three countries in Europe (UK, Denmark, and Norway) with the objective of determining how pesticide risk on golf courses varied as a function of climate, regulatory environment, and facility-level economic factors. The hazard quotient model was used to estimate acute pesticide risk to mammals specifically. Data from 68 golf courses are included in the study, with a minimum of at least five golf courses in each region. Though the dataset is small, it is representative of the population at confidence level of 75 % with 15 % margin of error. Pesticide risk appeared to be similar across US regions with varied climates, and significantly lower in the UK, and lowest in Norway and Denmark. In the Southern US (East Texas and Florida), greens contribute most to total pesticide risk while in nearly all other regions fairways make the greatest contribution to overall pesticide risk. The relationship between facility-level economic factors such as maintenance budget was limited in most regions of the study, except in the Northern US (Midwest, Northwest, and Northeast) where maintenance and pesticide budget correlated to pesticide risk and use intensity. However, there was a strong relationship between regulatory environment and pesticide risk across all regions. Pesticide risk was significantly lower in Norway, Denmark, and the UK, where seventeen or fewer active ingredients were available to golf course superintendents, than in US where hundreds of pesticide active ingredients are registered for use on golf courses.