June 25th

Hi All,

Apparently we had a bit of a technical glitch when I published this yesterday morning so we are trying again today Tuesday. Apologies for the delay in getting this to you, I blame the heat you know….

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Just one word to sum up this week, Scorchio !

Well as we edge towards the end of June it could go down as the driest June on record in some areas of the U.K and Ireland. Just 1.8mm here since the start of the month and 28 days since the last significant rainfall has cast a very dry shadow but hey it is summer 🙂

Before I go on to cover what will be a very straight-forward forecast for the week I had to include this picture of one of the inhabitants of my small garden. This Blackbird will typically walk up to the back door and look into the kitchen, fixing me with a beady stare that says only one thing…”Where’s my food ? “. Lately I’ve noticed if I resist his steely gaze for any length of time, he’s taken to standing on one leg….you could think that he was playing on the sympathy vote…As soon as I dispense some fat sprinkles and mealworms his way, his other leg pops out and off he trots….Birds are cunning creatures for sure…..:)

General Weather Situation

Image courtesy of Unisys Weather

Image courtesy of Meteoblue

 

 

 

 

 

 

With an opening shot on Meteoblue’s U.K and Ireland map top right, it won’t surprise you that this week needs no daily summary because quite simply it will be dry, bright and pretty hot with temperatures pushing into thirty degrees down south I think. That said, the only rain on this forecast is happening now over the west of Ireland as some heavy showers cross Galway and Mayo, they are few and far between though and will soon fizzle out. Night temperatures are likely to be low teens so that’ll make it uncomfortable enough for sleeping but not the worst we have experienced.

As you’ll note from the Unisys graphic (top left), the plume of hot air extends up from Africa into Ireland and the west of the U.K, so I expect these areas to pick up the highest temperatures with maybe some persistent-to-clear cloud cover across the east of the U.K towards the end of the week. I think Monday to Thursday inclusive will probably cover the hottest days and then we will back off temperature’s a little, more towards the low twenties as we see out the week and head towards the weekend. For some areas of the U.K, like us here in The Midlands, we will go out of June with barely a sniff of rain. You know the story…”It just went round us” 🙂

Weather Outlook

Last week I reported that the high pressure was due to break down the end of this week but now that doesn’t look to be the case even though we may lose some of the really high temperature for the weekend. There is a potential fly in the ointment rain-wise or maybe more aptly, a chance of some redemption if you’re desperate for some of the wet stuff. At the end of the weekend there’s a risk of low pressure developing down in The Bay of Biscay and that could edge up towards the south of the U.K and possibly Ireland on Sunday night / Monday morning bringing rain and possibly thunderstorms at a guess as moist air and warm air meet. That could be the only sign of rain though with unsettled conditions in the south of the U.K early next week before another Atlantic high pressure comes in and returns the weather to dry and settled conditions. I think next week will be cooler though with more in the way of cloud cover but with that low pressure close by it shouldn’t be a scorcher.

Agronomic Notes

Well no surprise this week that the main topic is managing stress (the grass plant’s that is) and the above Meteoblue lifted from Dromoland Castle in lovely Co. Clare provides a great back drop to chat through. It is broadly similar to one from Wales, England or Scotland for the coming week…

Watching Growth Potential becomes key during times like this…

The first point is the high GDD forecast, 96 in all which doesn’t incidentally mean we will have rampant growth. It is this time of year when GDD becomes less useful as a growth forecast model because it has no ‘top out’ figure for temperature, so if it gets hotter and hotter, the model assumes that the plant will grow quicker and quicker. Of course there are 2 problems with this assumption, firstly, as we got hot it is likely that moisture will be growth-limiting and secondly, grass species themselves have ‘top out’ temperatures above which their growth rate drops significantly as they go into survival mode. It does however suggest that a greens PGR application will probably only last 10-12 days at present.

Poa annua would have the lowest ‘top out’ temperature at anything above 27°C, with maybe the annual biotype a couple of degrees lower because of its shallower root system and propensity to seed more maybe ?

Ryegrass tends to get to 30°C and call it a day growth-wise shutting down its systems to conserve internal moisture levels.

Growth Potential as a model for predicting growth works better than GDD during the summer months because the calculation of G.P has an optimum temperature for C3 grasses of 20°C, though I use 18°C because I think it more accurately reflects stress periods such as the one we are entering now. So if the average temperature exceeds the optimum temperature for growth then you will see a decline in the G.P figure and that serves as an indicator of plant stress.

If we look at the Growth Potential part of the Meteoturf above, you can see it declines through the week and that’s because the model is predicting less growth due to stress. So if you enter a week of high day (and crucially) night temperatures and you can see your daily G.P forecast dropping then it is an indicator that plant stress is very likely.

The final part of the Meteoturf is the predicted moisture loss from evapotranspiration, in this case, 31mm. Now that is a significant amount of moisture to lose from the grass canopy over a 7-day period and it means you really have to be on top of your game when it comes to irrigating from your mains system and hand watering of course. This kind of weather tends to highlight any inadequacies in your irrigation system as well.

Poa annua isn’t always the first grass plant to check out in summer heat

Soil temperature can fluctuate significantly during periods of high air temperature and it is this kind of week when you really notice the negative side of having too much surface organic matter. Organic matter heats up faster than soil and retains heat for longer, once dry it is also very adept at repelling moisture due to the high root system component of thatch so irrigating high O.M turf can be a pretty inefficient process.

So what’s to do in a week like this ?

Plant Leaf N levels

Well firstly keep N levels sensible because if you push too much growth, the grass plant will need to take up more water to support the increase in shoot growth and that’s precisely what you don’t want at the moment.

It is though like most things in life, a balancing act, because we know that running low N levels in the leaf tissue will promote diseases like Anthracnose.

Image courtesy of Bruce Clarke, Rutgers University

Not the greatest image I’ll grant you, but this chart very neatly sums up the relationship between plant N tissue levels and the potential for Anthracnose.

Reading along the bottom ‘x’ axis we have total N concentration of plant leaf tissue and you can see that as we pass below 3.5% (reading from right to left), we dramatically increase the severity of Anthracnose, with 10% at a leaf tissue level of 3.5% and 60% at a leaf tissue N level of 3%.

The message should be clear then, if you’re running low N tissue levels during peak periods for Anthracnose development, you might as well put out a calling card for this disease. By the same token it isn’t about lashing N on, because as I’ve already said this can exacerbate the moisture requirements of the grass plant. The objective is  to achieve a balance in leaf N tissue.

Irrigation

Many of you will have moisture meters and so be ably equipped to know which areas do and don’t require supplementary moisture and how effective your hand-watering is.

You’ll also probably have your own guidelines too, knowing how low you can go moisture-wise before we see plant wilt and footprinting.  If you don’t have a moisture meter, an image like the one above should be a sure-fire warning that you are pushing the plant over the edge moisture-wise and if left uncorrected it will die. Irrigating doesn’t only provide the plant with moisture, it also serves another extremely useful function, that of cooling the soil surface and the plant leaf tissue.

I saw this yesterday at home where I have a flower bed with some really tall Rudbeckia plants (6ft high). They were wilting in the summer heat so I applied some moisture to the leaves to cool down the leaf surface and within 15 minutes they were looking great. It’s the same process when you have a shower, if you don’t dry yourself down properly you’ll note the very welcoming cooling effect on your skin that evaporating moisture plays. So syringing the grass during the middle of the day to wet up the leaf surface can really help well to lower plant stress. Be clear this isn’t irrigating per see, it is applying a fine mist to the leaf canopy to cool the leaf surface and thereby lower moisture loss.

Rolling not cutting

Since we have been dry for much of June, most of you will already be doing this so please forgive me if you think I’m trying to teach you to suck eggs. Missing a cut and rolling instead has been consistently shown to be beneficial to the grass plant during periods of stress and it is worth noting that the Anthracnose work at Rutgers University found no negative relationship between increased rolling and this disease, in fact the opposite. This was held to be because a firmer surface gives a truer cutting height from bench set to actual so you are putting the plant under less stress. Whilst we are on the subject of cutting height, raising it from 2.75 to 3.2mm has also been shown to be beneficial in reducing grass stress and Anthracnose. The use of more rolling as a substitute will also negate any potential loss in green speed. Skipping the clean up cut during stress periods is also a given for me because it is often here where you see the first evidence of plant stress and in particular Anthracnose.

Biostimulants

Some of the research work I am doing currently has shown that certain types of biostimulants (I’m not mentioning which because most of my competitors use a photocopier as a substitute for an R&D department 🙂 ) only produce a beneficial effect when the plant is under stress. So during periods of high temperature stress, biostimulant use is key and applying a good quality product can achieve positive results. If you are making a wetting agent application, combining the two is a 2+2=5 scenario for me. I saw this back in August 2006 when I was doing trial work on wetting agents and biostimulants.

During the trial I progressively decreased the amount of irrigation I was applying to the trial plots as a % of E.T. Once I got to 40% replacement of daily E.T (So on a 4mm E.T day I was applying 1.6mm of irrigation) I began to notice plant stress on most of the plots apart from the one where I had combined a biostimulant and wetting agent application. At the end of the trial (and during a very hot week when temperatures were up in the thirties) I turned the irrigation off completely and just watched the plots go backwards. They duly did but the one that stayed the healthiest for longest had the combination of biostimulant and wetting agent. Seeing is believing…..

Ok that’s it for this week, enjoy the sun, remember to use your sunblock and re-apply to areas where it is likely to be removed through the day.

All the best.

Mark Hunt

 

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