Hi All,


Can I have some more please ?

As I sit and type this blog, I’m watching an adult male Blackbird feeding his young on my lawn. The young Blackbirds are bigger than the adult and the food is on the lawn right in front of them but, despite that, they still call out to be fed… They must be the bird equivalent of modern-day teenagers i.e. very demanding and totally feckless… 🙂




After a weekend of two halves, where we had a muggy Friday night accompanied by thunderstorms, and heavy rain on Saturday then the heat of Sunday, this next week is looking a little similar with some rain to clear through in the early part of the week before some better drier and warmer days from mid-week onwards. So what’s changed? Well the jet stream is still split in two as the graphic below shows: with a northern section flowing over Greeenland and a southern section (the one that affects our weather) sitting over the U.K. The change is that the southern section has shifted higher and that’s allowing warmer air up from the continent.

Things aren’t normal though because it should be flowing in one segment, not fractured into two and that’s going to affect our summer weather for sure (how though I can’t be clear at this stage)…


Image courtesy of NetWeather

General Weather Situation


Image courtesy of Gywnn Davies

Well currently we’ve got some rain moving across Ireland and the western half of the U.K. and where that rain encounters warmth, there’s a likelihood of some thunderstorms for a time. I’m grateful to Gwynn for sending in this image showing some pretty sinister flat Stratus clouds signifying rainfall and an imminent storm. Through the morning, this rain is set to move eastwards across the whole of the U.K. but amounts shouldn’t be too high, unless you cop a storm that is… Scotland looks to start dry, but that rain reaches the borders by early afternoon and then you’re set for a wet end to the day. Temperatures should be pleasant, high teens to low twenties and winds will be light and from the south.

For Tuesday, we still have that mass of cloud circulating over the U.K. and Ireland, but through the morning it’ll push northwards into the north of England and Scotland, leaving the south of England dry. Ireland and Wales look to stay pretty wet most of Tuesday as that rain gradually moves northwards, but continues to affect western coasts. Temperatures will be high teens for most areas, maybe into the twenties in the Costa Del S.O.E (South of England) Winds will be moderate to blustery and from the south / south-west.

Wednesday is a much drier picture for most with that rain, now much lighter in intensity, sitting over the north-west coast of England and Scotland and slowly clearing through the day. Elsewhere it should be a much better day once the cloud has thinned, with nice temperatures up in the high teens – low twenties and light-moderate, westerly winds.

Thursday sees another dry day for most with the only fly in the ointment being a weak rain band that’s due to affect the west coast of Ireland during Thursday morning and then move into Scotland by the afternoon, giving a potentially wet end to the day there. South of say, the M62, it should be dry, warm and a very nice day indeed, with temperatures pushing into the low twenties, with a light-moderate westerly wind.

Closing off the week we potentially have an east-west divide as that rain is due to push south and affect the east coast of Scotland, England and Ireland during Friday, but since the rain band is narrow, it may easily miss us completely and just slink off into The North Sea. West and south of this, it looks another lovely day, with similar temperatures and winds to Thursday, maybe a little windier.

So how does the weekend coming look ?

Well we have high pressure in charge, so ordinarily I’d say it looks like being dry and warm, however because of the location of the high pressure system it’s likely to pull cooler air down from the north, so first off, the wind direction will be northerly. Secondly, some of that air will be moist, so it’s likely that we’ll see rain over the weekend, with a chance of showers over central areas on Saturday afternoon and again on Sunday, this time they look to be more westerly-orientated. With more cloud cover and a light northerly wind, temperatures will be down on the week previous, with high teens the order of the day. So sunshine and showers looks to be on the menu for the weekend.

Weather Outlook

This weeks nice warm weather is courtesy of a high pressure system, but next week this high looks like being squeezed between two low pressures and they eventually look set to push it out of the way completely, so I expect an unsettled week, next week. Rainfall-wise this means a return to rain at the start of the week, with potentially heavy rain from mid-week onwards, next week. Temperatures will still be reasonable, high teens I think and not particularly windy as no one system is set to dominate next week.

 Agronomic Notes

Well quite a lot to write about this week…

Growth Characteristics and the Growth Potential Model

From this point in the year, I’m going to start talking more and more about Growth Potential (GP), rather than Growth-Degree-Days and that’s because Growth Potential is a more accurate predictor of growth during the summer months as it takes account an optimum temperature for growth, denoted by a Growth Potential figure of 1.0 (the maximum it can be). Above that optimum temperature we know the plant begins to become stressed and so growth begins to decline, the Growth Potential Model takes this into account, Growth-Degree-Days does not.

A quick lesson, the Growth Potential is given by a value between 0 and 1.0, with 0.0 – representing no growth and 1.0 – optimum growth. The difference between Growth Potential and GDD is that with increasing temperature in the summer, GDD will keep on showing an increasing figure, whereas Growth Potential will not because it works on an optimum temperature for grass growth. For instance we know that once we get to 26°C +, the growth rate of Poa annua declines significantly, above 30°C it stops growing full-stop. So I think it makes more sense to start using GP to talk about growth once we start to build temperatures in the late Spring / Early Summer. I know a good few of you have been using GP for awhile now, there’s a link to a good paper explaining growth potential here

If you look at the last week or so, you can see we were sitting on around 0.55-0.7 from a growth potential perspective, but come the end of last week and specifically over the weekend, with the arrival of higher day and more specifically night temperatures, that figure has rose to close on 1.0. What this means is that according to the Growth Potential Model (GPM), the grass plant is growing at an optimum rate. A change in the GPM from 0.6 to 1.0 means a 66% increase in growth rate and an accompanying significant flush of growth. What’s more with the heavy rainfall (for some) last week and (for many) on Saturday, the grass plant is succulent, the leaves have a high water content and so appear soft and puffy.  This will gradually correct itself as high daily E.T. lowers the grass plant’s moisture content. If the plant is succulent, don’t go out with an aggressive verticut until it has lost some of that moisture else you’ll see alot of damage.

Growth Regulation by Trinexapac-ethyl (TE)

When I attended the GCSAA show this year, one of classes I sat in looked into the characteristics of Poa / Bent greens and the discussion moved onto the use of PGR’s. One of the Superintendents raised the point that his application of TE no longer provided the same growth regulation than it did when he first started using it. The lecturer dismissed this, however when asked for a show of hands in the class if other supers had seen this, it was significant and the lecturer was non-plussed.

It’s been mooted for some time now that one of the issues of this performance drop off relates to the breakdown of the TE molecule with temperature, the warmer it is, the faster this takes place, the less time it’s effective for, so one piece of advice is to shorten your frequency of application of TE when we get to the summer months.

However I believe we’re seeing something else. If you think about it, we’ve been applying TE to areas right back to the Shortcut days and the area that has received the most applications, on a regular basis, is fine turf, golf greens. Tees, approaches, fairways and sports fields receive less frequent applications, mainly due to budgetary constraints. (This where we differ from the U.S. which has much more frequent applications of TE and in fact pesticides in general on outfield turf)

Applying TE on a regular basis in my mind constitutes a selection pressure on the grass sward because we know it doesn’t affect all grass species / biotypes the same. So to my way of thinking, the grasses that is affects more, will grow less and the grasses that it affects less, will grow more. Over time, the grass biotypes less-affected by TE will surely dominate, now that might be a particular Poa or maybe Bentgrass, but either way I’m sure it’ll happen if the selection pressure is constant. So eventually you’ll end up with a sward of biotypes that are less-sensitive to TE and therefore you’ll have to apply more TE to achieve the same effect. I have no proof of this theory, it just seems logical to me.

So I’ll put out a question to you and I have to be mindful here of label rates,  so I suggest you are also 🙂

“Do you have to apply at a higher rate of TE than you used previously to gain a growth regulatory effect ?”

Now going back to Growth Potential, it figures that when we see an almost 66% increase in growth potential to a near optimum value, then you’re going to have to apply a much higher rate of TE than normal to gain adequate suppression of your grass sward. Looking at the the GP model, it’s clear that the trigger in this growth flush is night temperatures, if they are high, and by high I mean > 15ºC, then you can expect a growth flush at this time of year.

Of course grass growth isn’t the only parameter affected by the high temperatures and rainfall, disease activity is also significant at present and has been for awhile now as I discussed last week. Keep an eye out for Microdochium, it should grow out as fast as it appears, but sometimes that’s a tricky call.

After the wet winter and late Spring, I expect Take-All to be an issue on some high bentgrass content swards, specifically. It’ll only rear its head when the plant goes under E.T. pressure, like we saw yesterday when we had strong winds and high temperatures. In this scenario if Take-All has damaged the grass plant roots it appears un-affected until it needs those roots to replace significant moisture loss due to high daily E.T. rates and then you see the damage in the sward.

Looking ahead we only have this week before temperatures drop off again at the weekend and the weather becomes more unsettled, so things should settle down a bit thereafter.

All the best…

Mark Hunt