Golf Course Management

DEC 2018

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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74 GOLF COURSE MANAGEMENT 12.18 to growing Poa in the two native soils, but Poa annua growing in the greens mix was shorter, had fewer seedheads, seedhead branches and seed, and it took longer for the plants to pro duce a first seedhead. ese differences were likely due to the overall lower initial soil fertil ity of the greens mix. Although the plants were fertilized uniformly during the experiment, background soil fertility was not adjusted at the start of the experiment. Shoot weight and total seed weight in creased as the phosphorus rate increased. Ad ditionally, as the phosphorus rate increased, seedheads appeared earlier. When no phospho rus was applied, it took 127 days for a seedhead to appear, compared to 119 days to seedhead emergence when any phosphorus was applied. All of the other measured variables — number of seed, weight of that seed, number of seed head branches and germination of harvested seed — were largely unaffected by soil type or phosphorus rate. In general, Poa annua plants that were grown in soil with a high sand con tent and received no or lower rates of phos phorus were smaller and took a week longer to produce a visible seedhead. ese results could affect decisions about growth regulator appli cations intended for Poa annua seedhead sup pression. Sources: Guertal, E.A., and J.S. McElroy. 2018. Soil type and phosphorus fertilization affect Poa annua growth and seedhead production. Agronomy Journal 110:1 6. Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn Univer - sity in Auburn, Ala., and president-elect of the Crop Science Society of America. She is a 20-year member of GCSAA. Beth Guertal, Ph.D. guertea@auburn.edu Twitter: @AUTurfFert T is for turfgrass, and P is for Poa (verdure) Hate it, love it or tolerate it, Poa annua is a persistent plant in the turfgrass landscape. In fact, it is the only nonnative flowering plant species found in every continent in the world. Now, that is a plant that can adapt. Given its ubiquity in the landscape, turfgrass research ers have been studying Poa annua for a long time. Early work that examined soil character istics found that Poa annua was negatively af fected by high soil phosphorus or by low soil pH. at work was often conducted with a goal of keeping Poa annua in the landscape. However, in the southeastern United States, Poa annua is usually considered a weed, and research is conducted with a goal of reducing Poa annua populations. In 2010, scientists at Auburn University revisited phosphorus fertil ization effects on Poa annua, this time with a goal of determining whether phosphorus could be used to control Poa annua, rather than to encourage its growth. e researchers grew pots of Poa annua from seed, with the seed placed into three different soil types: a USGA type sand/peat greens mix (90/10 v/v), a clay soil, and a loamy sand soil. Before seeding, five rates of phosphorus (ap plied as triple superphosphate) were mixed into the pots of soil: 0, 0.5, 1.0, 2.0 and 4.0 pounds of phosphorus/1,000 square feet (0, 25, 50, 100 and 200 kilograms/hectare). After germination and two weeks of growth, plants were thinned so that there were five Poa plants in each pot, and they were allowed to grow until seedhead production and maturity. As the Poa annua grew, the number of days until the emergence of a seedhead was recorded. Once a seedhead matured, it was clipped, and the following in formation was collected for each seedhead: 1) number of branches on a seedhead, 2) number of seed on each branch, and 3) weight of the seed from each branch. After all the seedheads were harvested from a pot, the total number of seedheads, branches and seed, and the weight of those seed were calculated for each phos phorus rate/soil type treatment. Randomly se lected seed were then used in an experiment to measure percent germination. All of that clipping, sorting and weighing revealed that soil type and phosphorus fertil ization each affected the growth of Poa annua. ere were generally no differences attributed When no phosphorus was applied, it took 127 days for a seedhead to appear, compared to 119 days to seedhead emergence when any phosphorus was applied.

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