Hi All,

Well what  a Bank Holiday that was meteorologically !

The most amazing light show I’ve ever seen on Saturday night with constant lightning, thunder and then torrential rain.

Sunday saw some of the most active storm cells I have ever witnessed I think across the U.K and they were sparked off uncannily along the line of the M1 motorway and across London giving weight to the theory that hot concrete, hot cars, buildings, distribution warehouse roofs, etc act as the initial vectors for storms. (In the image below, the M1 motorway is directly under the path of the storms shown on the Netweather radar)

Image courtesy of netweather.tv and my I-phone

Some parts of Milton Keynes received 75mm of rain over a very short period and Birmingham once again was hit by flooding when 58mm of rain fell in one hour. It is no coincidence then that sometimes cities where we have lots of hot concrete, shiny roofs and traffic / hot cars are the focal point of these storms.

I’ve put together an archive of the lightning strikes over the last 3 days so you can see where it tracked ;

Ireland got its fair share of storms across the east and south-east by the looks of it. At the other end of the country, Scotland enjoyed beautiful Bank Holiday weather with temperatures on Monday tipping 30°C, so Smithy you owe me a Big Latte in Betty’s now matey 🙂

So after that tumultuous weekend, what have we got coming this week ?

Rainfall Forecasting

Before I give you this forecast, please remember my enduring caveat regarding continental rainfall and its unforecastability. No one forecast the deluges of Sunday, not even close. Here in Market Harborough we were forecast 15mm on Friday and got 21mm, then another 13.5mm on Saturday night / Sunday which wasn’t forecast and then we were forecast to get 14mm on Sunday and we got 1mm. My advice always is look at your rain radar, back click / forward click to see which way the rain is moving and then work out if you are in the firing line.

There are plenty of sites available now offering live rainfall radar simulations and they’re pretty accurate. I use Netweather.tv’s V7 radar which is claimed to be accurate to 500m and it seldom lets me down, I do pay a yearly subscription because I use their site for other information (Jet stream predictions, etc).

Here’s their current output for 10.45 a.m. Tuesday 29th May, looks like the south-east is in the firing line again for some pretty heavy downpours.

So Tuesday looks like following a familiar pattern of late, lots of mist and low-lying cloud across central areas initially and a cool start. Before long though the sun will break through and burn this cloud cover away to give a brighter 2nd half to the day. Further west across Wales, Ireland and west-facing coasts, that cloud cover burns off quicker so you’ll see the sun first. Now it won’t be long before that sunshine is replaced by the possibility of rain, some of it heavy pushing up from the continent into south-east England, (see above) along the south coast into South Wales and The South West later. So from late morning onwards we can expect to see some rain for these areas accompanied by thunder and lightning. Tricky to state how far north these showers will come because of the vagaries of this type of process but at this stage they look to affect the south of the country only. A lovely day again for Scotland and Ireland alike but for the latter a risk of some thunder storms later in the day I think. Temperature-wise we should see low twenties across Ireland, Scotland, England and Wales once the cloud cover has burnt off. A predominantly north-easterly wind as we have had for a while now will be moderate to strong.

Wednesday sees the rain from Tuesday carrying overnight and continuing through the first parts of the day. Again tricky to say where we can expect to see this but areas south of a line from The Wash to The Severn Estuary are most likely to be affected. Again some of this rain will be heavy and localised. Cloudier on Wednesday along eastern coasts but no such worries for Ireland as another corker of a day comes you way, the same for Scotland. With a north-easterly wind, western coasts will see less cloud and a quicker burn off rate to reveal long spells of sunshine. Some of the cloud cover across the north-east will be thick enough for some rain later in the afternoon. Low twenties again for Scotland, Ireland and some western facing coastal areas vs. high teens if you’re under that cloud and rain base layer which will clear from the south-east through the 2nd part of the day. A subtle change in the light winds from north-east to southerly is expected.

Onto Thursday and Scotland’s run of lovely weather is predicted to come to a halt as that north-east rain pushes cloud cover and rain into Scotland in the wee hours. I’d say it’ll track more westerly across Scotland initially so not everyone seeing the rain. By the morning rush hour we may also see some rain into the south-east of England and south coast of Ireland and this will push northwards across Ireland, England and Wales through the morning and continue to track northwards through the day. So a more patchy picture on Thursday with some areas staying dry and seeing the sun but more in the way of cloud cover and rain around for sure. Ireland’s rain should clear north through the evening to leave a nice one to end the day. Temperature-wise it’ll be hot across England and that may mean a reccurence of some thundery downpours on Thursday with the combination of heat and a moisture-laden atmosphere. Across Wales, Ireland and Scotland expect high teens, possibly just nudging twenty degrees, so not bad all in all.  Winds are expected to be light and from the south / south-east.

Closing out the week on Friday we have a more unsettled picture with thicker cloud and rain pushing into the East Anglia and The Midlands and then tracking north and west through the 2nd part of the day. Some of this rain will be heavy and localised, accompanied by thunder and lightning. Ireland and Wales see the thicker cloud from the off accompanied by rainfall but not everywhere will see that rain. That thick cloud base pushes north through the morning to bring rain to North Wales, The North West and Scotland for the 2nd half of the day. So an unsettled day on Friday possibly clearing from The South East and Southern Ireland late in the evening to give a brief glimpse of sunshine. Northern England and The North East though may see some very heavy rain with thunder and lightning on Friday night. High teen temperatures are expected in most areas and again the winds will be very light and from the south predominantly.

The weekend is looking likely to be cloudy and unsettled with the re-emergence of that north-east wind, albeit light. So westerly areas may get the best of the weather on Saturday / Sunday and there’s likely to be rain around again on Saturday, predominantly affecting eastern coasts initially before moving inland and pushing into The Midlands, north of England and later Scotland. This rain will push thicker cloud ahead of it and this cloud will be a feature of Sunday as well, particularly on eastern coasts. Sunday looks drier, but still plenty of cloud cover because of that wind vectoring in off The North Sea. Temperature-wise I’d say high teens at best, a couple of degrees lower if you’re under the thicker part of that cloud base.

Weather Outlook

Really kind of strange weather lately because no one strong weather system is dominating. Instead we have a real mix of weak fronts and that makes forecasting especially hard I think, but here goes…

So next week looks like a weak high pressure system will remain in charge and so I think we will see a mainly easterly air flow and dry, settled conditions with little rain. I don’t think it will be stupidly hot, more pleasant like with high teens and low twenties the order of the day, probably more of the former than the latter. Around mid-week we see low pressure try and impose from the south so that means a possibility of thunder, lightning and rain but at this stage it is projected to miss us.  I think this could well change as we approach next weekend but at present dry and settled for all. If anything I expect the north and Scotland to hang onto the warmer temperatures next week and particularly at the end of the week.

Agronomic Notes

With the combination of high rainfall, temperature and humidity, I think we will see (or have already seen) quite a lot of turf maladies pop up.

Looking at the weather for my Midlands location over the last week you can clearly see the sudden increase in overnight temperatures on the 25th May and the high overnight relative humidity..

So the above combination will have given rise to some Microdochium nivale pressure for sure but with ideal growing conditions I don’t think this would have necessitated a fungicide application. (though some will have maybe wanted to use up any of their remaining Iprodione before the use up date in the first week of June)

You can see the high daily Growth Potential at the start of this week carrying on from last week…

So diseases like Microdochium will grow out as fast as they appear and once the sun is out and humidity drops markedly, so will the disease pressure.

Now I would also expect some of our more common summer diseases like Waitea Patch, Superficial Fairy Ring and possibly Rhizoctonia on shaded sites with poor airflow and high humidity (Stadia in particular) to also begin to show from now on as humidity and elevated soil moisture levels combined with high temperatures ramps up the pressure from these diseases.

Anthracnose Trigger Points

We know from past seasons that Anthracnose requires consistent days of 25°C for spore germination to take place. What it also needs through the same period is high humidity as well because the fungus isn’t a really strong grower outside the plant and needs plant leaf wetness / high levels of soil moisture to complete the initial phase of infection as a Biotroph. Thereafter it will sit in the plant taking some of its food reserves but not destroying plant cells. It appears to require a further trigger to become necrotrophic (killing plant cells) and studies suggest that this trigger could be when the plant goes under stress.

Now that can be heat stress and / or nutrient stress with clear research findings indicating that a plant maintained at a consistently low N status (I’d say below 3.25% leaf N tissue) more likely to be affected by the disease. Drought stress initiated by high temperature is another pre-cursor to the necrotrophic phase of this disease and of course when a plant is under drought stress it is unable to uptake sufficient nutrient from the soil (as the soil moisture level is too low to provide nutrients in soil solution. Work by Rutgers University has shown that maintaining nitrogen levels > 3.6% and potassium levels > 2.0% are key to reducing the severity of this disease, with nitrogen the stronger of the two influencing factors. In fact nitrogen was the strongest influencing factor and so the most important BMP when you are managing this disease, much more important than fungicide application. Anthracnose as a disease is one where putting the correct BMP’s in place can significantly reduce the impact of the disease regardless of pesticide use.

So far in early May we have had some days of consistently high temperature but looking at the weather station output for the same period it was accompanied by low humidity because it was warm, bright, sunny and windy. So I don’t think the early May weather was a signal for Anthracnose spore germination. I will analyse data from around the U.K and Ireland over the coming week to see if this past week has met the conditions for the biotrophic trigger for Colletotrichum cereale.

Even if the weather meets the required conditions for Anthracnose spore germination and initial fungal development, if we don’t then get periods of prolonged plant stress, we may not see the disease. Looking at the last 3-4 years, 2014 was the last year when we had a very hot August accompanied by high daily rainfall levels as well at times, in other words perfect for fungal development and plant stress and that’s when we last saw very aggressive Anthracnose foliar blight. Since then August has been a bit of a damp squib with persistent rainfall and cooler temperatures (I hope you haven’t booked your summer hols for this month :))

One last point before we leave this disease, genetic studies have shown two distinct genetic lineages for this disease, termed Clade A and Clade B, think of them as families within a population. Clade A is known to more frequently affect Poa annua and Clade B, Agrostis stolonifera. That’s why in the U.S, where they have both Clades present, you see references to this disease not only on Poa annua but also as a serious disease of Agrostis stolonifera. Over here we tend to see this disease mainly affecting Poa annua and so it is likely to be from a population belonging to Clade A. (10 distinct Anthracnose populations have been isolated worldwide on turfgrass and these populations either belong to Clade A or B)

Interesting eh ?

That’s it for this week…

All the best.

Mark Hunt