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What Is Poa Annua And

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What Is Poa Annua And by STANLEY J. ZONTEK, Eastern Agronomist, USGA Green Section Over the last decade and a half numerous ther testing until finally it became widely articles have been written on the various means publicized and used by some superintendents, of controlling Poa annua. The earliest talked especially in the mid-west and Eastern areas. about literally cutting Poa annua plants out of During the 1960s, pre-emergent crabgrass kil- the putting greens. An article that appeared in lers (Balan, Dacthal, Pre-San, and Betasan) were The Bulletin of the Green Section of the United shown to control Poa annua seed germination. States Golf Association in July, 1922, stated They worked reasonably well and their use for that Poa annua was removed "with a knife, Poa control has now become rather extensive. with a hole cutter, with a chisel or any other I n recent years the growth retardant chemi- tool that may best suit according to the size of cals (Endothal and Po-San) have come into use the patch infested." for Poa annua control. Principally, their mode How then did Poa annua develop into such a of action is to limit seed head formation and major turfgrass species from its meager begin- thus reduce the potential for a re-growth from nings as a common weed? The answer princi- seed which is the primary means of Poa pally I ies in cutting height and water. With the annua's dissemination. advent of improved irrigation systems and the Finally, a relatively new material called Kerb desire for closer cut turf, Poa annua popula- is finding popularity for Poa annua control on tions increased and took over the major playing many bermudagrass fairways today. It has areas of the golf course. I n the beginning this performed very we". takeover was encouraged because Poa provided Whatever means of chemical control used, a beautiful playing turf for several weeks of the the goal of the user is the same-to erradicate year, usually in the spring and fall. The Poa Poa annua so its inherent weaknesses do not annua was the one grass species that could give the type of playing conditions that the thrive under the close cuts, excessive water and membership finds objectionable. As with most the compacted soil resulting from foot traffic chemicals, an understanding of how it behaves on continually moist soils. The heavy soils used is essential to success. in early construction techniques only aided its development. Therefore, when the Poa annua Poa Annua-The Weed turf thinned during the summer and member- Exactly what is Poa annua and why is it ship pressure dictated a green grass cover at all considered a weed? Annual bluegrass (Poa times, extensive study was given to means of annua L.) is a native plant of Europe. Over controlling Poa annua on large turf areas. centuries of emigration it has distributed itself over all the world as a contaminant in seed Poa Annua Controls mixtures. It is sometimes referred to as annual From the 1930s through the 1950s, lead meadowgrass, winter grass or simply Poa. Its arsenate was widely used for Poa annua control. leaves are I ight to yellowish-green in color; the The mechanism by which the arsenical selec- plant is low growing; it is capable of producing tively suppressed the Poa was not completely seed heads at various times during the growing understood at that time. Practical experience, season and at extremely low cutting heights. however, had shown that it did in fact work, so Poa annua has the unique abil ity to produce lead arsenate was used for Poa annua control on viable seeds capable of germinating only one to greens. On fairways its use was usually imprac- two days after pollination. It has been reported tical and was not extensive. that a single Poa plant has produced 360 seeds During the late 1950s the use of tri-calcium in a four-month period. arsenate was being tested and studied. Its Why then is Poa annua considered a weed? erratic early performance would result in fur- I n most areas and under certain conditions, JULY 1973 Comparative pictures of balls on putting greens. Excellent lie with a ball resting on Poa annua putting green turf. annual bluegrass is a weed. Simply defined, a the cool humid regions of the country. I n these weed is a plant that is out of place. areas, some refer to it as "failure grass." On putting greens in the South a heavy Poa Because Poa annua is classified as either a population during the transition months tends summer or a winter annual, once the plant has to shade the desired bermudagrass species and died there is no re-growth from its roots or slows its emergence from its winter dormancy. stems. The plant is dead. Any re-growth comes I n some cases this results in a painfully late and only when the seeds that were disseminated slow transition resulting in poor playing condi- earlier in its life cycle can germ inate and grow tions. I n the North it is considered a weed into mature plants. As stated before, the because of its competition with bentgrasses and undependable nature of the grass is its greatest Kentucky bluegrasses for the dominant grass Iiabil ity, but there are others. species on the main playing areas of the course Poa Annua is highly susceptible to almost all (greens, collars, tees and fairways). When Poa turfgrass diseases, both summer and winter. The annua is only a small percentage of the total extent of "winter kill" is also greater. In regard grass population on the course there are few to putting qualities, there are times when very problems. However when the population be- heavy seed head formation causes bumpy, un- comes a majority, the possibility exists that the even putting surfaces, especially late in the day Poa could be thinned out or entirely lost during after mowing. Varietal differences within the the summer stress period. This poor summer species have a similar effect. Different volunteer performance is the principal reason why Poa varieties have different growth rates, growth annua is considered a weed under most cool- habits, seeding habits, leaf widths, etc. These season turfgrass cultures. factors affect putting qualities. Although Poa annua may not thatch as heavily as bentgrass on greens, it does develop Other Poa Annua Weaknesses grain and puffy ness, especially at higher cutting Exactly what are other annual bluegrass heights. At lower cutting, it becomes more weaknesses? When subject to severe cold, difficult to hold during stress periods. This grass drought or heat, Poa annua has a difficult time does not take traffic as well as bentgrass, surviving. Unfortunately, two of these stress particularly during high temperatures. Recovery factors (heat and drought) often occur during from any kind of stress is also restricted in hot the summer at the height of the golf season in weather. Poa annua requires very critical and 2 USGA GREEN SECTION RECORD Bentgrass t :; also a fine lie. careful management at all times. Even then the prime seeding time, Poa annua can make success can swiftly slip away. one of the finest playing surfaces that we have today... if it can be kept from dying. See Poa Annua Strengths figures 1-5 on the comparative lies resulting With all these real and apparent weaknesses, from the various turf species grown in the why is so much Poa annua grown in the cooler cool-season regions. As the pictures illustrate, regions? Perhaps one reason is that when Poa Poa annua makes for excellent lies equal to or annua is right, it provides one of the best even better than the other grasses. Therein lies playing surfaces for golf that we have! A good the incentive for most superintendents who stand of Poa forms a fine textured turf of high have accepted the challenge to maintain it. shoot density, uniformity and quality under almost all cutting heights ranging from 1/8 inch Managing To Maintain Poa Annua to over one inch. Its leaves are usually shorter, Superintendents and their golf clubs often broader, softer and lighter green than most prefer Poa annua turf. They find renovation varieties of Kentucky bluegrass. This also makes programs too long, expensive, and painful to the grass easier to mow. Field data, along with play during the year. Therefore, the question research has shown that annual bluegrass has a has been asked, "What management practices root system comparable to Kentucky bluegrass can we perform to help the annual bluegrass in density and depth. It can survive and thrive survive and thrive the year-around?" Following under compacted soil conditions that deter the are some steps that we feel can be performed to growth of both bentgrasses and Kentucky help make this possible. bluegrasses. It produces a good supply of viable (1) Watering. Irrigate a lot, in fact every seed under all cutting heights assuring self-per­ day. In the heat of the summer, syringe once or petuation. It grows well in the sun or shade and twice a day depending on the temperature and is in fact one of the north's best shade grasses. humidity. With higher temperatures and higher It is quick to germinate and re-form a turf humidity, there is a likelihood of more kill. naturally when conditions are right. It affords Also, higher wind-blown spots generally require an excellent lie for golf balls due to its upright more watering. In this all-important syringing growth habit and strong blade that keeps the operation an automatic irrigation system would ball from nestling down into the turf.
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