I’ve had a number of emails regarding the potential for snow over the coming days and I also wanted to pass on some feedback in a quickie update.
General Weather Update
The issue for the next 5 days is that we have moist air from the west meeting up with cold air from the east and with a low pressure pushing an easterly airstream across the U.K and Ireland, this means there’s a high possibility of snow, but as far as I can see, not too much.
For Friday, we have a band of weak rain pushing diagonally (\) across the U.K and Ireland, but we’re talking patchy light rain with most places staying dry, although cold, dull and foggy. Overnight that rain band meets cold air over the north Midlands and the east coast and that’s where the highest potential for some snow is.
Later on Saturday, moisture from the North Sea pushes further snow showers onto the east coast in a line down from Scotland to The Wash. For Sunday morning, rain over Leinster and east Munster pushes into Wales and again there’s a potential for snow/sleet lunchtime Sunday here. There’s also a likelihood for some snow showers coming in over The Wash and pushing down the east coast of England. I remember when I was working in research in Cambridge at N.I.A.B, my lab faced east and I used to watch the snow coming in over The Fens in just such a manner 🙂
At present the highest snow risk looks to be on Monday as a rain front pushes in from the west having started off over Ireland early doors. This rain is orientated in a straight line (|) and so as it moves eastwards duirng the morning, there’s a likelihood it’ll turn to snow for a while. After that we have some respite, but my mild front will only be around for a day or so before more cold, wet lows push in. So staying unsettled, with more rain, sleet, potentially heavy at that for next weekend and the immediate future. Frost-wise I think we’ll be picking up night frosts from today onwards, though not heavy ones until Sunday, as always it depends on cloud cover for your location.
The subject here regards Fusarium activity over the last week and particularly around old scars present from before Christmas. From Christmas Day through till Tuesday this week, soil and air temperatures have been high for this time of year, with a number of double-figure, night-time temperatures and prolonged periods of leaf wetness due to rain and/or dew. By and large, I haven’t had many reports of new, aggressive disease activity- though I wouldn’t discount it – but I have had reports of potential activity on the edge of previous, pre-Christmas period scars such as the one shown below and I wanted to talk about this.
What we often see in this scenario is that the area around the edge of the scar appears darker, often with mycelium and this suggests activity. It is also often the scenario that a fungicide has been applied before-hand and the question is ‘Is my fungicide working? If so, why am I seeing this activity?’
If you look firstly at a cross section of the disease scar, the lowest pathogen population is in the middle of the patch and highest population on the edge because, as the blue arrows indicate, the disease is moving outwards. Since fungicides work by reducing the growth rate of the disease population, they are least effective in the area of highest disease population i.e. the edge of the disease scar so, we have a critical balance in this area:
Growth rate of pathogen population vs. Suppression of growth rate by the fungicide
If environmental factors, leaf moisture, air/soil temperature are increasing the growth rate of the pathogen at a higher rate than the fungicide is able to control, the net result is that the disease population increases and so activity is noted in this area.
As the environmental conditions abate, i.e. temperature drops and the leaf dries out, the driver behind the disease population decreases and the fungicide affects the population at a higher rate and you achieve control.
There is often a lag in this process as the plant takes out sufficient fungicide A.I to achieve control and this is particularly acute during the winter when growth rates are lower. If the grass plant is healthy, then uptake of any fungucide is more efficient and control is achieved at a faster rate. You still though have potential for the above scenario to exist, albeit for a short period of time.
So, my point is this; if you have recently applied a fungicide and have subsequently seen signs of activity around older scars, the above scenario is the one likely to be occurring, particularly during mild, damp periods of weather. Now that we’re cold, the driver behind aggressive disease activity will decline (but not disappear because frost does not kill Fusarium) and you should achieve control.The caveat to this is if your plant is weak going into this period, uptake will be slower and therefore potential control poorer.
If in doubt, mark the area of the outside of the scar (see above) with a couple of small marker paint dabs and watch to see if the disease continues to move outwards. You must of course give the fungicide sufficient time to enter the plant and this will be a function of fungicide chemistry, application timing and plant nutrient status / growth rate.
Hope that helps, have a good weekend.