Best Technical Merit Answers- June 2003
Following the success of the Technical Merit Award 2003, sponsored by Tillers Turf. Pitchcare have started to publish some of the best answers submitted to the monthly scenario questions. This month we have the best of June's answers. Next week the best answers to the July's scenario question will be shown.
June Scenario Question:
June- Annual meadow grass (Poa annua) is not the most desirable species for a high quality sports surface. Describe all methods that you might employ to reduce Poa dominance in the sward.
1) Methods of Poa annua control and elimination. If, as I have, you enter the words Poa annua control in to a search engine on the Internet, you will find there are three thousand nine hundred pages available on the subject. This shows the amount of interest there is in finding a solution to the problem of controlling Poa annua. Control of this grass species can be narrowed down to two methods one being cultural and the other, chemical control. Prevention is better than cure.
Poa is so opportunistic and persistent once established; it is vital that the desirable grasses in a sward are kept in peak condition so as to avoid bare patches that Poa will almost certainly invade. High phosphate levels are generally believed to contribute to Poa infestation, as are alkaline soils. So a balanced level of nutrients coupled with a pH below 7.0 will be a good foundation for providing soil that discourages Poa annua. Good management of soil moisture content and nutrient levels can help to discourage Poa annua and encourage other species such as Agrostis and Festuca.
Compaction is also a significant factor Poa thrives under wet and compacted soil conditions. Due to its shallow root system, Poa can tolerate lower soil-oxygen levels, on which turfgrass stands tend to thin There is a theory, with which I agree, that the advent of automatic irrigation systems has contributed to an increase in Poa annua in poorly managed surfaces. Before the flick of a switch could produce water in vast quantities, irrigation was carried out on an as-necessary basis. This meant that the more drought tolerant species such as the Fescues and to a slightly lesser extent Agrostis spp. flourished rather than the moisture loving Poa.
With the advent of pop-up sprinklers, misguided and badly trained greenkeepers and Groundsmen have used the application of water as a cure-all for problems, which, more often than not were being caused by over-watering in the first place. Modern day irrigation systems, when used correctly can apply very precise amounts of water and can be an aid to Poa control rather than a cause of Poa invasion. The incorrect use of fertilisers, and in particular excessive applications of Nitrogen and Phosphate can also lead to problems from Poa annua. A high available-nitrogen supply encourages profuse Poa germination, growth and tillering. Research indicates lower annual nitrogen rates encourage more bentgrass and less Poa. A balanced application of water and nutrients along with a regular programme of aeration will provide conditions that are less favourable to Poa annua survival.
However, swards that do receive the highest levels of professional attention by outstanding turf professionals still suffer from Poa invasion. Chemical control. At a time when chemicals can be used to control and regulate so many other things it is testament to just how difficult selective control of Poa is. Although Poa is considered to be a weed by many, it a grass with a similar genetic make up to other grasses. It is therefore incredibly difficult to produce a chemical that will attack Poa and not other species. It has been common practice when trying to eliminate Poa to apply Glyphosate or a similar non-selective weed killer, kill off all vegetative matter and re-seed with desirable grasses. This form of "start from scratch" approach is often the only answer when Poa annua has become the overwhelmingly dominant species.
Recently a chemical called ethofumesate has been shown to be extremely effective in preventing Poa from establishing on newly sown turf, and controlling Poa that is present, but only minimally, in the sward. Poa annua in golf, croquet, bowls and other ball roll sports can, if managed well provide a good or even excellent surface. The story is different in sports where a consistency of ball bounce and pace are important, as is the case with cricket and lawn tennis.
In 1999 the Sports Turf Research Institute began a trial investigating the use of ethofumesate to control Poa annua in lawn tennis courts. The study was carried out over two years. Ethofumesate is the only chemical in the United Kingdom that is licensed for use as a control for Poa annua. The STRI investigation concludes that ethofumesate can be very successful in controlling Poa annua in grass tennis courts. (Andrew Newell, STRI January 2003) It also says however that the timing of application and application rates are critical to success and that there are unwanted side affects to the desired grasses after application of the chemical. There are five other chemicals that I know of which are being or have been used in trials for Poa control, all in America.
Also in America there is a product called Prograss, which has shown excellent Poa control results, and, unsurprisingly, the active ingredient in Prograss is Ethofumesate. It is extremely difficult to control this most opportunistic and tenacious of grasses. From a cultural control standpoint, although there are conditions where only Poa annua will survive, there appears to be few situations where it will not. Millions of dollars are being spent on producing chemicals to control it but despite these resources, only one appears to have had any significant success, and even ethofumesate has it's limitations. This is why millions of dollars are also being spent on developing a "user friendly" variety of Poa annua.
To summarise, Poa annua once established is almost impossible to control and for this reason, turf managers have learned to work with it to produce excellent surfaces. If you can keep on top of it, it can be subdued and the methods mentioned above can help achieve that.
2) The dominance of Poa annua in a sward depends on the management practices employed according to the type of sward required. Bents and Fescues have different requirements than Poa annua, and to a lesser degree so does perennial ryegrass.
An understanding of the different requirements of individual grass species is important, and can be utilised to formulate a management program that favours the desired grass species.
Here is a list of management practices that can reduce/ control Poa annua in a sward: 1. Correct water management: Poa annua has shallow roots, so watering should be carried out heavily and infrequently to encourage deeper rooting from the Bents and Fescues, and weaken the Poa annua with drought stress. If irrigating light, frequently it is worth pointing out that Poa annua, can absorb water quicker than its rivals, so watering lightly on a hot day is only likely to Favour one grass species. Spiking before irrigation, with either a sarrel roller, or something deeper, to increase the infiltration rate of any precipitation and again encourage the deeper rooting species to dominate.
2. Correct fertiliser management: Adding unnecessary fertilisers is not only bad for the environment, but also bad for the sward. Fertilising the surface of the sward will only encourage shallow rooting and Poa annua. A correct informed approach to soil fertility will ensure that the desired grasses have sufficient for their needs. The amount of Phosphorous in a soil has been proven over 100 years ago to be related to the persistence of Poa annua in swards. Correct analysis of this macronutrient will be necessary to ensure that the correct levels are maintained. With golf, in particular Bents and Fescues it is worth remembering that they thrive on poor soils. What might be a deficiency for perennial ryegrass is not necessarily one for Bents and Fescues. It is necessary for perennial ryegrass to be fertilised more than Bents and Fescues, by spiking before application you can reduce the amount of nutrients that Poa annua can absorb. A final point would be that clay soils retain more nutrients than sandy ones.
3. Removing worm casts: During the winter months switching should always be carried out before mowing, especially on fine turf such as golf greens. Smearing bare patches into the sward will provide the perfect seed bed for Poa annua. Surfaces that are not required to be cut so short during the winter months can have their worm casts controlled using a light raking technique. During the winter months on the cricket squares I prepare, I always once a fortnight push a Sisis "lawnman" over the square will the rake attachment when conditions are favourable. Not only does this control casting it also prevents the accumulation of thatch and drags out any weak growth (such as that of Poa annua). Less thatch more air movement a drier sward, could there be another benefit?
4. Regular aeration- reduces compaction: Annual meadow grass copes better with compaction than finer grasses. Remove the competitive advantage!
5. Renovate bare areas as soon as possible: Bare areas can be a result of wear, disease, mowing faults, worm casts, etc; these should be over-seeded at the earliest opportunity. Any bare area will soon be utilised by Poa annua, unless the desired sward is sown first. Broad-leaved weeds can be controlled by herbicides, but weed grasses are more difficult. Prevention is better than cure!
6. Reduce rate of compaction: Avoid working on areas when they are too wet. Walkways and traffic routes should be marked, to avoid damaging other areas. Use machines with either low ground pressure tyres, or are lightweight.
7. Boxing off clippings: Collect clippings, collect seed heads! The surface of the sward can also be swept to collect seed heads, or raise them for removal with mowers. 8. Buying good quality seed: Poa annua can be present in bought seed, therefore it is important to know exactly what is in the seed bag before it is purchased, read the seed certification! It is possible to buy seed with little Poa annua seed in it, however it is more expensive.
9. Top dressing with suitable materials: Top dressing materials should be sterilised before being applied to any sward, to prevent weed and weed grass seeds from contaminating the sward. Ensure that the top dressing is compactable and that it has the right pH, not alkaline - especially for Bent and Fescue swards.
3) There are a few proven ways to reduce Annual meadow grasses on the greens. One way we use is to hollow tine, top dress and then over seed with high quality pure bent grass seed, by doing this it encourages stronger grass species to grow which are more resistant to drought and disease.
Another way is to verti-cut while the annual meadow is seeding and mow the seed heads off this stops the Poa Annua from spreading. Other techniques can include keeping the ground dry and not over watering in summer as the annual meadow does not like dry/drought conditions.
One method which is still being tested, I believe is to improve bacteria and AM fungi in the soil. This can be done by many products now available with organic matter, which is full of the bacteria (bio-organic fertilisers) proven to encourage stronger species of grass such as the bents.
This also helps with resistance to disease and therefore saves money and time on applying fungicides