Monthly Archives: August 2014

August 18th

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Hi All,

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No frozen props on this one Iain …..

After a very warm July, August continues to disappoint, as we remain stuck in a trough pattern in the jet stream which is allowing low after low to drop down and bring cooler, moist air into play.  I was at Sywell Airshow yesterday and one minute  it felt like summer, the next everyone was trying to shelter out of a harsh and cool north-westerly wind :(

For the start of this week we have particularly cold air as the low pressure is drawing air down from the north and that’ll make it feel more like October than August, particularly during any of the sharp showers that we’ll see this week and at night :(

General Weather Situation

A pretty easy forecast as the week is effectively split into two parts with Monday through to the close of play on Wednesday set for a brisk northerly / north-westerly wind to dominate proceedings and this will rattle in showers across the U.K and Ireland through the course of the day. These will tend to affect the north and east of the country during this spell, but they’re just as likely inland later into the afternoon. Temperatures will definitely feel chilly compared to what we’d normally get at this time of year, especially during those showers and under cloud cover. That said, find an area out of the wind and during the sunnier spells, it’ll feel quite pleasant. So mid-teens probably the best we’ll see and in that wind with the windchill, it’ll feel closer to high single figures, so definitely an extra layer required. I’d like to be more specific with the rain showers but in my experience it’s not worth it as they can and will pop up anywhere, one place might get clattered and another 4 miles down the road will be dry as a bone..So that sets the scene for Monday to Wednesday, unsettled, a cool north-westerly wind and some blustery showers with cool night time temperatures.

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So by Thursday we have that low exiting stage right onto the continent and that’s due to a change in the wind direction swinging round to the west and moving it off the U.K and Ireland. So Thursday will feel a little warmer, however it won’t be dry for some as rain moves into the north-west of Ireland / Scotland/ rest of the U.K (wonder how much longer I’ll be saying that for?) during the morning. It does try to push south, but it’s likely that from The Midlands down in both countries will stay dry for the whole day. Later on that rain pushes onto western coasts and into Wales, but again it’ll mainly affect North Wales. Closing out the week the boot may well be on the other foot for Friday with that rain pushing into Munster and then swinging round into the south-west of England and Wales and pushing north-eastwards. So it’s more likely that the west and south will catch the rain on Friday, particularly later in the day.

There’s a suggestion that the rain will hang around into the first part of the weekend, so that may mean a wet start to Saturday for some, particularly in The Midlands and south of England. Plenty of time for that to change yet though so I won’t be digging out the boat baler quite yet. Either way it looks unsettled for the weekend particularly for Saturday in the south of England. Elsewhere it’ll still remain on the cool side especially at night when mid-single figures may be the order of the day. At this stage Sunday looks the better day of the week, but as a new low approaches it’ll bring cloud and then rain into the west of Ireland later on on Sunday and then to the west of the U.K for Sunday evening.

Weather Outlook

The above gives a hint for the start of next week with a new low projected to influence our weather and bringing strong southerly winds and rain, initially for Ireland and the west on Monday , but I expect that to push north and east through the day, so possibly a wet start to next week on the cards and a wet Bank Holiday for us over here. So a pretty unsettled start to next week with westerly winds and strong showers the order of the day I think. It’ll probably feel a little milder than this week because of that westerly airstream.

Agronomic Notes

Etiolated Growth – ETS

Plenty of this around at the moment because of the change in weather conditions and the cooler, damp weather. Had a good bit of feedback about the topic last week, with a number of you pointing out that you sometimes see more ETS on approaches, but not on the fairway or green on the same hole, so my theory of more annual biotype Poa showing ETS doesn’t look to stand up to scrutiny. I’m going to try and do some isolation work on this kiddy through the autumn so if it comes to anything I may update you in my fringe seminar at Harrogate.

That rain is packing some N

For the 2nd rain water sample in succession I measured around 1.25kg / N/ ha / inch of rainfall falling last week and with a pH of 5.0, it was quite acidic as well. This shouldn’t be a suprise as I’ve noted before the pH of rainfall dropping from it’s usual 6-6-6.7 region to a more acidic pH, when it originates from a ‘stuck’ weather system that’s doing a few laps of the U.K before moving off…

Growth Flush ?

The combination of rain and a warm soil mean that things are really growing fast at the moment, especially on outfield turf so it may be prudent to reach for a PGR, however if you look at the night time temperatures forecast I think that’ll drop the soil temperature and the rate of growth naturally. You can see from the predicted growth according to the Growth Potential model that we’re dropping right off this week right down to 0.25 (25% of optimum growth) so maybe just keep the PGR in the Chemsafe for the time-being.

GPAug2014

Worm Activity and Sulphur

After the dry July and now a cool and wetter August, I’m starting to see very early signs of worm activity on outfield areas. Some of you are using sulphur as a way of acidifying the soil prior to a Carbendazim application and often the advice is to apply these products together in the spray tank. SulphurpH

All well and good until you realise that it’s actually the conversion of sulphur in the soil by specific microbes (Thiobacillus) that provides the acidification rather than the sulphur itself. The chemical equation is shown above and if you can remember from your school chemical classes, it’s the hydrogen ions (H+) that are responsible for acidification. This conversion may take 3-4 weeks after application of the sulphur before it has achieved the desired effect so the trick is to apply the sulphur first, then the Carbendazim later once the soil surface has been acidified.

General Disease Activity – Fusarium & PGR juggling…

I’m expecting with the cooler temperatures that we’ll see some Fusarium start to raise its ugly head, so this means the balance between regulating growth and disease has to be thought about. Mind you we may not get much dew this week because of the strength of wind during the night…..

That said, it’s no good sitting there and banging on 400ml of TE because it’s August when you take a look at the anticipated Growth Potential stats above and realise that growth on greens / fine turf is going to take a significant dip this week anyway. We should also consider that with some diseases (and I believe Fusarium / Microdochium) is one of them, you can / do lower the disease intensity by physical removal of fungal mycelium on the leaf when you cut. So the rub is to find the balance, maybe lower the application rate of PGR or skip it completely for this application. My comments are specific to fine turf and with outfield I’d suggest there is a case for application though again we have to be mindful of the relationship between PGR’s and the severity of Red Thread in particular.

On other fronts I think the disease pressure from PPN’s, Fairy Rings and the like will be reducing with the drop in temperature, but I don’t think summer’s quite over yet, though it may seem that way for the time-being..

Ok that’s it for this week, I may skip a week next week as I’m on hols, depends on the fishing and the surf :)

Mark Hunt

August 11th

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Hi All,

Just back from a quick trip to my motherland, Danemark, so apologies fophoto 2 (2)r the late sending of today’s blog. It’s difficult sometimes to compare a country you visit for a short while with one where you live, but I have to say, Denmark has the edge for me :) They are quite simply more realxed, more sussed and organised than we are and they measure everything !!!!!!!

photo 1 (2) If you’re ever over on Jutland and have some hours to kill, take some time to visit the sand sculptures up at Søndervig, north of Esbjerg, quite amazing to think they can make something like this out of just sand and water !

I gather while I was away sipping a cool Tuborg or two, that more than a fair drop of rain came our way and judging by the headlines from the east of England and the amount of standing water visible from the plane on the bumpy approach to Stansted, it was torrential in nature. I did suggest that might be the case in last week’s blog because of the way the weather patterns were shaping up and I can tell you that it’s highly likely to re-occur again during August, though not necessarily in the same place. I emptied nearly 50mm from my rain gauge since last Wednesday, so for sure we’ve had a clattering….

General Weather Situation

So since Monday is pretty much on the way out, I’ll start with Tuesday’s forecast.. So Tuesday is looking to continue the unsettled nature of the weather this week with heavy rain into north-west Scotland from early doors and also edging into the west of Ireland, the south-west and west coasts of England and Wales by the morning rush hour, pushed along by a strong south-westerly wind. Through the morning, this rain will track eastwards, so many places getting some rain on Tuesday. Temperatures will be similar to Monday, so high teens and they’ll dip a bit at night to low teens.

This pretty much sets the scene for the week, with showers affecting the west coast of Ireland and the U.K and taking most of the day before they’ve tracked eastwards to affect the east and south-east of England.

For Wednesday we have a very similar picture, with rain showers affecting the north and west of Ireland and the U.K from early doors. These showers will track eastwards, so most places catching more than the odd one, but it’ll be sunny in-between the showers, particularly for the east and south-east of England. Temperatures will be similar to Tuesday both day and night and the wind will moderate a little as it swings round to a more westerly orientation.

For Thursday, we continue that unsettled theme with more sunshine and showers kicking off on the west coast of Ireland and the U.K and tracking east through the day.  The wind will be a little lighter, but it’ll also feel a little cooler as it swings round to the north-west, a portent of things to come me thinks….so mid to high teens the order of the day.

Closing out the week we have a similar picture, so dry for the south and south-east of England, but those showers are already kicking off for the north of England, Scotland and along the west coasts of the U.K and Ireland. Through the day they’ll track across country and again the east and south-east may stay dry all day and miss the majority. Temperatures will again be similar to the rest of the week in that strong to moderate north-westerly wind, so mid to high teens the order of the day and low teens at night.

Weekend-wise it doesn’t look so bad with perhaps the driest days of the week on Saturday and Sunday. They’ll still be showers around and these will be heavy over north-west and central Scotland. On Sunday the wind will shift temporarily round to the south-west and this will pick up temperatures into the high teens, maybe touching twenty degrees. Enjoy it because it’s downhill from here weather-wise.

Weather Outlook

As intimated above, it looks like next week’s weather could be potentially dire, especially for the south-west, Wales and south of England. Not great news when you’re considering spending 5 days in a camper van on the cliffs at St David’s :(

Monday could be the quietest day of the week wind-wise as the wind begins to change direction, swinging round to a more north-westerly / northerly direction. Despite the spaced-out isobars, Monday does look like starting off wet for the west of the U.K, Wales and Ireland, though the heaviest rain may only affect the south of Munster and perhaps Donegal. By Monday evening and overnight into Tuesday it’s looking like a heavy pulse of rain will push into the south-west of England and affect a line drawn down from The Humber. At the same time it looks like more rain will push into Scotland. By mid-week we’ll have heavy rain over the U.K and Ireland pushing westwards on a cool and increasingly strong, northerly wind. Thursday and Friday look better, with less rain and quieter winds, we may even see some sun :)

Agronomic Notes

Trinexapac-ethyl (TE) and Summer Usage

We’ve had a good bit of discussion over the summer to date about the frequency and rate variation experienced on greens and other areas with TE.  A good number of you have commented upon the lack of efficacy at certain points in time when applying TE at 2-3 weekly intervals, with sudden increases in growth despite the recent application of a product.

In the U.S as many of you will know they use a TE / GDD model based on 0°C and apply TE every cumulative 200GDD. Some of you have commented that this still gives growth surges and have cut the figure to 150 GDD, i.e applying every cumulative 150GDD, so I thought I’d look to see what this actually meant using some temperature data provided for me by an end-user in the south of England for July 2014.

The column highlighted in blue is the daily GDD using 0°C as a base. The cumulative column next to it simply adds each day to the previous days total and so forth. I have marked in yellow the point in the month when the GDD figure reaches 150 and you can see that if you followed a 150GDD / TE model it would mean applying on the 1st July, 9th July, 17th July and 24th July, in other words, on a weekly basis to keep growth consistent.

ParkstoneGDD0Base

The perceived wisdom from the U.S is that application of TE on fine turf surfaces should be performed at a greater frequency, rather than at a greater rate, during high temperatures and this would appear to be the case here as well.

So how have people got on applying at 150GDD ? Answers on a postcard please……

Poa annua – Love it or hate it, You’ve got to be impressed…..

You may remember earlier in the year I posted a pic of 3 Poa annua plugs I took from a golf green and ‘potted on’. They were all displaying different physiological characteristics and I found that fascinating. Well I’ve been ‘growing them on’ and all they’ve had is an application of 4-3-4 and some biostimulant. Well they’ve colonised the whole pot now such is the aggressive nature of Poa annua and it’s tillering ability !!!!

In addition, I was suprised to see the root development, ok I’m not cutting at 2mm, but the root mass and depth is excellent. Lastly in this species never-ending quest for world domination, it’s also seeding at the edges of the pot so it can colonise the surrounding area (My kitchen sink !)

Poa pot start Poa pot now Poa pot roots

Core look at that !  (sorry about that, couldn’t resist it)

Poacore2

Keeping on the Poa theme, I had this lovely picture sent to Me today of a Poa annua core that is being used to establish a new turf area using core transferral. This increasingly popular method involves ‘transplanting’ hollow cores from established greens to a newly-rootzoned area and working them into the surface. The idea is that the sward which then develops is ‘mature’ in nature and so you suffer far less during the transition phase of Poa encroachment and also you directly replicate the playing characteristics of your other greens on a new turf area. So the new green / turf area fits in much better than a seeded or turfed area would do and importantly has little of the inherent organic matter content associated with established turf.

Getting back to the picture you can clearly see new tillers / shoots of Poa appearing from along the profile of the core. In other words these have to have orginated from the seed bank that Poa annua creates in a rootzone profile. With this and the top pictures in mind, how do we ever think we can keep it out from most turf situations ??

On the green – a quick round up…

With the rainfall of late falling onto warm soil, I confidentally expect a lot of Etiolated Tiller Syndrome (ETS) to be doing the rounds. Some observations from the field seem to suggest that it’s appearance and distribution is possibly linked to the distribution of annual Poa annua biotypes, as opposed to perennial biotypes. In other words it would appear to colonise areas that have thinned out at some point in the recent past or on higher height-of-cut turf areas where we know there’s a higher population of annual biotypes. (Because we see them seeding first here in the spring….)

I’ve had a good few reports of pecking on turf surfaces and although some people have suggested that it’s down to Leatherjackets, I think we also have some high populations of Cutworms as well because of the winter and spring weather. If it is Leatherjackets, how come we didn’t see high populations of Adult Crane Fly 8-10 weeks ago, I know there were some around, but not lot’s….????

I’m wondering if the cooler and wetter weather of this week and next will encourage an early outbreak of Fusarium /  Microdochium ? I know from agriculture that there is a very high incidence of Microdochium in Winter corn samples this year and I wonder whether this will translate to high disease pressure for the late summer / early autumn  – Again your observations would be appreciated…

Lastly there’s plenty of Anthracnose and Plant Parasitic Nematode activity at present, sometimes they’re occurring together which makes life pretty interesting. It seems to be the Ecto-parasitic species that are occurring the most often, i.e Spiral, Stunt and Sheath…..

Ok that’s it for today, need to get sPolseome pedal miles in between the showers because I’m carrying a few extra kilo’s from my Danish experience, too many Pølse I’m afraid,,, :)

All the best…..

Mark Hunt

August 4th

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Hi All,

After the heat of last week, we can down to earth with a bang with some pretty heavy rainfall, The east of Ireland copping a packet to start their Bank Holiday weekend with 84mm falling at Dublin Airport and 54mm in Mullingar !

Here I have to say we needed some rain and we got 12mm on Saturday morning, which you guessed it, filled up my boat and resulting in a very soggy flyfishing session, the term ‘dry flies’ was not appropriate !

We’ve not finished with the rain though and this coming week promises more heavy rain on the cards, with Wednesday and Friday looking a bit grim. It’s courtesy of a low pressure system that has dropped down into a trough in the jet stream. I don’t want to sound alarmist but typically if / when this occurs in August, it usually brings with it some very heavy rainfall.

General Weather Situation

Monday starts the week off dry for most of the U.K and Ireland, except for some lingering rain over north-west Scotland. Elsewhere we’ll have a pleasant day with hazy sunshine and temperatures just touching 20°C after a cool start (with dew). Later in the afternoon, a rain front moves into west Kerry and Connacht to bring rain for the late afternoon / evening. Winds will be light and from the south-west.

Overnight into Tuesday that rain pushes north and eastwards across Ireland into Leinster and also affecting the south-west of England, Wales and the north western coasts of the U.K, including Scotland. As we go through the day, that rain affects a line drawn diagonally north from Bristol to The Wash. South of this it should be another pleasant, dry day with temperatures up in the low twenties, but in the afternoon there’s a risk that some of this rain may sink south to affect London and the Home Counties. That rain over Central Scotland looks to be stuck in for most of the day unfortunately. Temperatures will be a little cooler as the wind swings round to the south, maybe just nudging across the 20°C mark.

As we move into Wednesday, we see the first signs of a slow-moving low pressure weather system that’s due to affect our weather from Wednesday through to the weekend……

So we have a heavy rain pulse moving into the south-west of England, Wales and north-west Munster, south-west Connacht in the early hours. By morning rush hour, this pulse is over the entire south-west of England and Wales and tracking north and eastwards to cover most of the country by late morning. Ireland looks to dry out after this early morning rain to leave a fine day.  By the afternoon, that rain is set across England and Wales with Scotland missing the worst and as we approach the evening it clears the west and central areas, but may linger on eastern coasts. Again the wind stays set in the south, moderate in nature with temperatures down on Tuesday under that cloud and rain.

Moving on into Thursday, we have a much drier day on the cards save for some rain over north-west and the Highlands of Scotland. Elsewhere it’ll be a pleasantly warm day with lots of sunshine and temperatures up in the high teens / low twenties.

Clsoing out the week we may, I say may, potentially have a very wet end to the week, courtesy of a pulse of heavy rain up from, you guessed it, the continent. I say may because as we all know, this type of rain is extremely unreliable in terms of amounts and location affected, so keep an eye on your Weathercheck portal closer to the time. At present it’s saying that a rain pulse will push up from France into the south-west of England around morning rush hour and then track northwards with all areas getting rain, but the heaviest looks to be central and western parts, rather than the east of the U.K. Ireland is also likely to get rain later in the morning, pushing into Munster and tracking northwards. This rain front looks particularly heavy and slow moving so flooding is likely and by late afternoon it’ll still only be sitting over The Midlands, so very slow moving in nature. As we close out Friday that rain will have cleared the south of England and Wales and will be affecting the northern and border counties before moving into Scotland late on Friday night / early Saturday morning.

So how does the weekend look ?

Well that slow-moving low will be sitting off the east coast of England so it’ll be dragging down rain into Ireland, Scotland and the west of the U.K on Saturday morning, with that rain pushing eastwards across the U.K in the afternoon, so maybe dry a.m. for the south, but the rain won’t be far away. Sunday again looks the better day, but with a new low lining up to take the place of the departing one, I think the west will be unsettled on Sunday with an ever-increasing westerly / south-westerly wind.

Weather Outlook

Well as mentioned above, next week looks like starting off very unsettled due to an Atlantic low pressure system that’s rattling in. I expect it to bring high winds and heavy rain to Ireland and the west on Monday and for that rain to spread across country during the day. So windy, from the north-west, unsettled and with frequent showers during the early part of next week and it’ll feel cooler, with temperatures in the high teens only :( From mid-week we pick up some slightly warmer air, so the winds start to drop, the rain eases off and potentially it’ll be a little better, but staying unsettled and cool for August in that north-west wind.

Agronomic Notes

Lots to talk about this week…..

GDD / Growth Potential Spreadsheet – Data Entry Issue

We have a slight issue with the spreadsheet we provided at the start of this year to record GDD and GP figures. The August tab on the spreadsheet doesn’t allow you to enter minimum temperatures, so needs a slight, simple tweak. The instructions are ;

1)      Open the Log file in Excel

2)      Select the August Sheet

3)      Click on the ‘Review’ tab

4)      Click on the ‘Unprotect Sheet’ button

5)      Save the Spreadsheet

That should do the trick, any problems, just drop us an email in the usual way, thanks to Graham for highlighting this issue

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Abbreviations

A number of you have asked about some of the abbreviations I use in my blog, so Paul has inserted a tooltip which highlights the abbreviations in blue and if you pass over them with your mouse cursor when you’re reading the blog, it’ll open up an explanation of the abbreviation as you do so, very clever, cheers Paul….

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Disease Activity – Anthracnose

After the very hot and dry (for many) July, we now have a familiar August breakdown in the weather with rain, some of it heavy. In my mind this creates a perfect storm for Anthracnose and indeed I’m starting to see / hear quite a few reports of this disease. Last week I was doing some moisture readings on a golf course to look at fluctuations with respect to green situation / organic matter levels, etc and interestingly I found one area affected by Anthracnose Basal Rot. The area was a low point on a green and the moisture readings were around 40.0% (they’d had 8mm rain the previous night), whereas other areas were in the low twenties.

It highlighted to me how useful a moisture meter is from a diagnostic perspective, ok we don’t need a moisture meter to tell us that a low spot will have higher levels of moisture, but it certainly helps to quantify how much more moisture that area was holding and of course if you change irrigation strategies, you can monitor the effect much easier, rather than sticking your finger in the air and saying, it’s drier :)

Going back to Anthracnose I expect aAnthracnose Damage high incidence of the disease this August bearing in mind the rainfall we’ve had / going to get and the heat in July. From a prevention perspective, good balanced nutrition is key, so either light and frequent foliar N applications or a light rate, summer granular fertiliser are the order of the day. Work in the U.S found nutrition was key to controlling / preventing Anthracnose, almost as effective as applying a fungicide and a lot cheaper !

Anthracnose – Remedial Action after the event

If you already have signs of Anthranose, then the normal path is to apply a fungicide, but personally I think it’s one of those diseases that by the time you see it, it’s too late for a fungicide to be effective because the base of the plant is already infected and dying off, so chances are you’re going to lose that grass plant whatever you do. A fungicide will merely ‘ring fence’ the affected areas. To get quick recovery from Anthracnose, you need to lightly aerate, raise the cutting height if practical, fertilise and topdress, as well as dropping your PGR rate to allow the plant to grow back / tiller across the affected areas. Don’t be taken in by the “It doesn’t grow upwards it’ll tiller better with a PGR” spiel because I don’t think it’s true, particularly for Poa annua.

Incidentally there’s been no correlation with increased rolling and Anthracnose activity in USA research, in fact they found less disease in the more rolled plots…Why ? because the rolling is firming the surface which means the actual cutting height is more similar to the bench set height, rather than is the case where a softer (un-rolled) surface allows the mower to sink in a little and cut shorter than the bench height. (Thereby applying more stress)

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Moisture Meter Readings

TDRNot the greatest of pictures I’ll admit, but it shows 2 different designs of moisture meter side by side sampling turf. The Delta-T model is reading 29.9% and the Spectrum 28.2%. Now obviously there’s variability in turf even on supposedly homogenous rootzones, but I consistently found that the Delta-T was reading 1.5 – 2.0% moisture higher than the Spectrum and I think it’s because of the different rod lengths between the two meters.

The Delta-T Theta Probe comes fitted with 60mm rods as standard, whereas the Spectrum can be 38mm, 75mm, 120mm or 200mm depending on the spec at purchase. The one I was testing against had 75mm rods.

This isn’t a case of right or wrong in terms of the product or manufacturer, just a note that if you’re comparing readings with the guy next door, then if you’re not using the same meter, they probably will be different. Also I’d say that this practice is pretty irrelevent anyway because what matters is how your greens perform at an ideal moisture level and that ideal moisture level is specific to your course, rootzone, grass species, green situation.

Anything we can measure in turf invariably results in a d*** measuring exercise in my humble opinion, so I’d suggest concentrating on what works on your course, taking and learning from your own observations accordingly :)

And more disease….

Lot’s of Waitea, Superficial Fairy Ring, Thatch Collapse, Plant Parasitic Nematodes, etc doing the rounds at the moment and with the recent and forecasted rainfall I’d expect a big hit of Etiolated Tiller Syndrome (ETS). I’ve covered all of these diseases in my recent blogs so I won’t be repeating myself, don’t worry :)

GDD Data

Wendy has kindly updated the GDD data for the year, so we can see how it compares…

GDDmonthlycomparisonandcumulativeJantoDec2010to2014image

You’ll note that July 2014 had a very high GDD, similar to 2013 and much higher than previous years, however we know that this isn’t the whole picture for July because of the heat and E.T levels, so let’s look at those now…

High E.T = High Plant Stress

Looking at some of the statistics for July 2014, we can see that it was an extremely high E.T stress month, particularly the last 3 weeks. Using Sean’s data from The Oxfordshire, we can see the following ;

Month& Year                      Total E.T Loss                Rainfall    Moisture Deficit

July 2013                              109.7mm                       39.4mm       -70.3mm

July 2014                              135.6mm                       36.4mm       -99.2mm

I’ve charted out the month this year so you can see how the rainfall and E.T stress panned out ;

DailyETRainfallJuly2014

Effectively the moisture deficit was 99mm in 2014 and 70mm in 2013, so it shows just how hard a month it was in some (but not all) locations.

The consequences of this type of weather are many ;

Firstly, it really highlights how well or how badly your irrigation system is at coping with this sort of water replacement requirement.

Secondly all the consequences of this type of weather, be it dry patch, stress-related diseases like Anthracnose or Plant Parasitic Nematodes, come home to roost in the intervening weeks.

Growth Potential Models

I mentioned last week that I thought the optimum temperature for calculating Growth Potential (GP) at 20°C was inaccurate for Poa annua surfaces over here in the U.K. Micah Wood, one of the key academics involved in the Growth Potential Model was kind enough to drop a comment detailed below on the blog ;

“I think it is a great idea to adjust the optimum temperature in the growth potential equation to match the observed turfgrass growth. That is the whole point, really, to generate a number between 0 and 1 that is representative of the influence that temperature has on allowing or not allowing growth. Jason Haines in Canada has worked with GP adjusted with optimum temperature of 18 for his Poa annua greens. A blog post on that is here:

http://www.turfhacker.com/2013/11/growth-potential-fertility-after-2-years.html

So I looked at two sets of data for July, one from Long Ashton Golf Club, courtesy of James Braithwaite (cheers James) and the other from Sean at The Oxfordshire (Ta Chuck) and then charted them out looking at the maximum and minimum air temperatures during July and the GP calculated using 18 and 20°C. The results are interesting to say the least ;

gpjULY2014

Firstly, looking at Long Ashton G.C, you can see there is a moderate dip in both GP models at the beginning of the month, (6th, 7th, 8th July) but it’s a much sharper dip for the model based at 20°C, compared to the model calculated at 18°C. I didn’t see a pronounced shut off in growth during this period, so I think the model based at 18°C is a more accurate description of observed turf growth. Towards the end of the month 20th-24th, we can see another dip in the GP trace, but here the dip is much more pronounced on the GP model calculated at 18°C, with a near 30% reduction in growth potential. Again I think this is an accurate portrayal of actual events because we did see growth of Poa annua shut down during this period.

Looking at The Oxfordshire, the graph is much more variable, with more peaks and troughs than Long Ashton and that’s because of the very open nature of the site at The Oxfordshire. It heats up very quickly because there’s little shade preventing this occurring and it loses heat to the atmosphere at night more quickly as well. You can see that when the minimum temperatures for early July at Long Ashton were rarely below 10°C, at The Oxfordshire, they dropped to 6°C. In contrast, the maximum temperature recorded at Long Ashton was 30.2°C on the 25th July, it reached 32°C on the 23rd of July at The Oxfordshire.

So use of the Growth Potential model for me is showing two things, firstly that we need to modify the optimum temperature to 18°C to give a more accurate portrayal of observed turf growth and that by highlighting dips in GP when temperatures were high, it gives us an expression of applied plant stress and so provides a predictive measurement for the consequences of that stress, like Anthracnose for example.

So we’ll see in the next 7-10 days whether those two dips towards the end of July were sufficient enough to generate increased disease activity from Anthracnose or not…Please keep me posted on what you see out there because without your feedback this blog is limited in its effectiveness.

I’m off to sunny Denmark for my annual family gathering, so hopefully I’ll miss that bloody great low pressure system…good waves though :)

All the best…

Mark Hunt