Tag Archives: GDD

May 28th

Hi All,

Spare a thought…

You’ve got to feel sorry for the grass plant at the moment :(….On Friday, it got blasted by cold, northerly winds with a windchill temperature of just 5°C and to add insult to injury, cold rain as well, that dropped the soil temperature down from 13.5°C to under 10°C. Saturday was a gentle reprieve, but for many a slight ground frost started the day…by Sunday, the same, but the wind was picking up and starting to exert an E.T stress, that by Monday had risen to 4mm a day in hot, dry, gale force, southerly / south-westerly winds. So it’s not surprising that it isn’t up to much in terms of greens growth, particularly when we’re cutting low to provide consistency of surface, ho hum 🙁

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Haven’t we been here before ?

I have a certain sense of déjà vu typing this blog, particularly when I look at where we were a year ago, jet stream and hence weather-wise. As you can see from the graphic below with the two months placed side-by-side, the jet stream is still prone to slipping south and hence letting cool, wet air follow it. The difference for me is that this year instead of it staying put, it keeps fluctuating from this to a peak and back again, and so we have the scenario described above in terms of wildly fluctuating weather. I know things must be bad weather-wise because I’ve taken to listening to The Verve and Morrisey again ! 🙂

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General Weather Situation

Well for this week, we’re in a trough again for most of the week, so that means staying cool and with the ever constant threat of rain, with a lot of places receiving a dollop – 20mm + on Tuesday. Friday looks a better day (hence I’m taking it off) before the weekend slips back again into that trough, but there may be better news round the corner, so read on 🙂

For Wednesday, we still have that Atlantic low pressure in charge so a cool, wet day for some, with that rain band from Tuesday still lingering in a horizontal line (-) from above the Thames Estuary to Wales. Above and below that, it’ll be drier and brighter, but for the south of the U.K, that’ll only last till mid/late morning when that rain band will slowly sink south and give more rain before fizzling out. Ireland should be much better with a sunny day in prospect after the clouds break in the morning 🙂 After lunch, a new front of rain pushes into the north east of England / south-east Scotland and tracks south-west into The Midlands and Wales / South-West England later on in the day to conclude with rain. For Thursday, we have another nice sunny day for Ireland, whilst the dry start in the U.K is temporary with a rain front extending from Edinburgh to Eastbourne (sunshine capital of England apparently, but not this day Andy !) during the day and only the east and west coasts of the U.K staying dry. On the bright side, temperatures will be a bit better for Wednesday and Thursday, reaching mid-teens during the day, and remaining up at night, so that means thumbs up for greens growth (but also disease I’m afraid). Winds will be from the north, peaking on Thursday. Friday sees that trough in the jet stream temporarily dissipate, allowing warmer air across the U.K and Ireland, though the winds will remain from the north. The skies will brighten and by mid-morning, most areas should see the sun, yes, the sun, that’s the yellow thing. Ireland will have a duller day and some light showers, particularly across Leinster. Later on Friday, cloud cover will build again and that may bring some light rain overnight across the north of England and The Midlands, but this should clear on Saturday morning, the first day of June (already!!???) and not a bad day in store for Saturday with hazy sunshine and reasonable temperatures for many, though they’ll be more cloud cover and the risk of light showers across Ireland and Scotland, later in the day. Sunday looks if anything slightly better, particularly for the west and Ireland with more sunshine and nice, pleasant temperatures…smart. Crucially for me, we’ll keep good night temperatures, so that means greens growth should kick off in the latter part of this week.

Weather Outlook

Next week, looks like starting off dry and settled for many with high pressure, yes that’s high pressure (!) building, light westerly winds and temperatures moving up into the 20’s, I think. There’s still a threat of rain towards the end of the week, particularly to Ireland and the west, but at this stage, things look appreciably better for the start of June than they did for the start of May ! Now wouldn’t it be nice to have some dry and settled weather for a change 🙂

Agronomic Notes

Growth-Degree-Day Data and its interpretation

Got the nod on Friday night that the blog and more importantly the GDD data was a subject of discussion (thanks Matt, Claire) on the BIGGA forum and wanted to tackle the subject matter / questions raised whilst it was still fresh in my mind.

The question related to the unit of measurement of growth-degree-days on the vertical axis, as unfortunately in last week’s blog, the graph wasn’t the clearest due to the limitations of the WordPress layout (the software I use to do my blog).

Before I do,  please remember there’s a comment option on each blog that I publish, so you can ask a question, raise an issue, whatever and I do read and answer every one of them. If you prefer to, email me directly, the same comment applies in terms of answering, with the only exceptions being whilst fly fishing, riding my mountain bike or blatting along on my VTR 🙂

Growth-Degree-Days (GDD) are a method of measuring / quantifying the plants growth potential, year-on-year and rose to prominence originally I think in agriculture, but later, they were adapted for turfgrass growth, primarily for the timing of PGR’s with respect to seedhead suppression. An excellent article written by Karl Danneberger on GDD’s is available here who explains GDD’s better than I can, except to say that the model I have created starts on January 1st of each year, (because the grass plant is easily capable of growing in January, as has been shown the last 3 years), is calculated in °C and I use a base air temperature of 6°C for my calculations, as I believe this is required for the initiation of shoot growth on our resident grass species.

GDD’s are calculated using the following formula ;

( (Maximum air temperature + Minimum air temperature) / 2 ) – Base Temperature

(with base temperature fixed at 6°C)

So, if a day has a maximum air temp of 15°C, a minimum of 5°C, and a fixed base temperature of 6°C, the GDD calculation is as follows ;

((15 + 5 ) / 2) – 6   =  (20 / 2) – 6  =  (10) – 6 =  4

As Karl explains, there is no unit for a GDD model, it is simply a number summarising growth potential on any one day and cumulatively, over a given length of time. I’m in the process of trying to link this number with actual growth as measured by clipping yield, but it’s early days yet. So what use is it ?, well it provides a quantifiable measurement of grass growth in a given year for your site and already it has shown me the impact that shade has on this process. In turn you can use it to demonstrate why growth is where it is, i.e slow, normal or flushing.

I can also state that for this year, Poa annua var. annua started seeding in earnest when the cumulative GDD reached 154, which was on the 7th May and Poa annua var. reptans started seeding in earnest when the cumulative GDD reached 191.5, which occurred on the 19th May, nearly 3 weeks later than normal in my books. So GDD data provides a benchmarking model for growth, day to day, month to month and year to year.

Looking at the GDD data for May, we can see what a topsy-turvy month it has been growth-wise, with some distinct peaks and troughs continuing right up to last weekend with a growth check on Friday 24th and Saturday 25th. (low GDD figures)

 Grass growth – The current state of play

The constant ‘stop-start-stop-start’ temperature pattern, so typical of May is causing its usual issues for many on managed turf areas, but I always work on things not really stabilising till the end of May and in particular night temperatures. It is these that are the key to greens growth and I think we will see a gradual pick up as the week goes on and especially from next week. So if you’ve fertilised and nothing much is happening at present, hang fire, before applying on top of the previous application because if you do, you’re likely to get a 2+2=5 growth scenario, if the projected weather stays on track !

Outfield Turf is go !

Just watching the local council guy cut the rec behind my house. I can remember him in April zipping along with scarcely a grass blade flying in the wind, such was the lack of growth back then. Now there’s a bow wave of clippings from his units as he struggles to get on top of the growth !

So if anything I’d be looking to put a PGR + iron mix pretty much top of my list regardless of the type of turf you maintain (golf, sports, etc) because with the rain of this week, gradually increasing soil temperatures (courtesy of those milder nights) and warmer weather on the horizon next week, I think we’re going to see a significant growth flush, particularly on higher-height of cut areas, if it hasn’t already started for you.

“My turf is puffy, slow and unresponsive

With the Poa plant putting a lot of its efforts (and food reserves) into producing seed, the leaf is pale and coarse, puffed up by high soil moisture levels and the sward is soft and slower than usual due to the presence of seedheads.

I got tipped me the nod to an excellent blog (ta Sean) compiled by Golf Course Superintendent – Adam Garr from across the pond at Plum Hollow Country Club, which according to Google Maps (isn’t the Internet great for this kind of thing ???) is located just north west of Detroit, in Michigan State. Adam has put together some great features on specific areas and a couple deal with Poa seedheads (yes they do have them there too you know 🙂 ), click here for an ‘aggressive greens program’ approach to seedheads.

It made me smile, shake my head in awe and feel a bit depressed how far we are behind over here and at the fear of alienating anyone reading this blog, there are so many turf management situations that we deal with on a day-to-day basis, reactively, in fire-fighting mode, which could be prevented by good, practical, cultural maintenance beforehand, if time, money, resource and most importantly, the will and understanding (often from above) is there. The heart of the problem is of course, our poor economic situation, and the plain truth that the threat of revenue loss is king now. Trying to overcome the ‘If it ain’t broke, don’t fix it mentality’ that exists higher up in many circles is hard work…there are exceptions of course, but they are few and far between. (refreshing as they are though when you encounter them)

OK, I’ll get off my soapbox now and deal with the issue that initiated this slight digression. In Adams blog above, he remarks on the loss of 2ft of greens speed due to the onset of Poa annua seedheads and I think the puffier, broader leaf that accompanies them also plays a part in this. High soil moisture levels also promote a thicker leaf and we’ve had plenty of that of late, so all this adds up to slow greens speeds for many and for those maintaining sports pitch scenario’s, the appearance of pale, clumpy grass within the sward.

If the projected weather patterns come about, they will initiate a number of positives to help us manage the above. Firstly, they’ll dry the plant out, so the leaf will fine down, for all grass species that is. Secondly, the growth will allow us to employ some good cultural work, that is verticutting, grooming, brushing, topdressing to begin to manage proactively the mix of grass species present AND get reliable growth / recovery thereafter from our fertiliser regime. Lastly, we’ll be able to control soil moisture levels, firming up greens by utilising targeted hand-watering where it is required. (labour and climate allowing of course)

 Disease Activity

A number of reports of Fusarium doing the rounds, not surprising really with the high soil and leaf moisture levels and when you chuck in some milder nights this week, it could become quite aggressive in places, so be on your guard. Fortunately if we do dry out, that’ll both lower the disease pressure and give us the chance to initiate recovery without having to spray necessarily.

I’ve also seen some Plant Parasitic Nematode (PPN) damage on my travels, which at first glance looks like Fusarium or maybe Anthracnose. (see pic) Both Endoparasitic and Ectoparasitic species are active and the patches tend to show if the sward is at low fertility or has recently suffered a high E.T (Evapotranspiration) event. Ultimately the rub here is to maintain a healthy plant, make sure nutrition is balanced, so not over-fed, nor under-fed. Aeration to generate new roots, unaffected by the PPN’s is also key as will be regular biostimulant applications to suppress plant stress if it does go hot and dry.

Pathogen Complex Effects – PPN + Pathogenic Fungi

One key point pertinent to what we’re seeing at the moment is that it maybe the case that both PPN’s and a disease like Fusarium are active on the grass plant at the same time, working together in a complex. This was first described by Kate Entwistle (no ‘h’ mind) and  Colin Fleming and it’s a bit of a chicken and egg scenario – i.e the PPN weakens the plant and that exaggerates the effect of the plant pathogen …in these cases it means just treating the turf disease (e.g. Fusarium) doesn’t always result in alleviation of the symptoms or recovery is unusually slow. According to Kate, Fusarium and Anthracnose, are the most-often encountered turf diseases that can occur in the presence of a background level of PPN’s…the giveaway that a complex scenario may be at work is that the disease keeps re-occurring in the same location on the turf surface, i.e the same part of a green or a football pitch.

Turf symptoms caused by plant parasitic nematode species and a pathogenic fungi (Fusarium)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In 9 times out of 10 PPN situations, there’s normally at least one if not two contributory factors (shallow rooting, high E.T days increasing stress, low cutting height, compressed fibre, poor rootzone physical structure, etc) that increase the severity of PPN damage and often dealing with these will also lessen the effect of the nematode, without having to apply a control product. If in doubt, get a sample off and Kate will put you straight :), click here for contact details.

Chafer Activity

A lot of golf courses have seen grub activity this Spring, particularly Leatherjackets, but Badgers, Foxes and Corvids looking for Chafers have also caused significant damage, particularly early in the season when food elsewhere was scarce. For guys managing Chafer Grubs, I’d be interested in any observations of adult Beetles or new juvenile grubs throughout the year, so if you wouldn’t mind, drop me a comment or an email…cheers in anticipation.

Ok that’s all for now, back to the grind…:( or 🙂 as the case maybe

Mark Hunt