"I've got about 15% disease" is a regular statement I hear when talking to people and I never really know what that means.
I'm always looking for quicker and more reliable ways of measuring turf disease and I think I've come up with a good'un.
What always surprises me is how far out people are with there estimation of %'s and therefore what an inaccurate way it is to express how much disease you have. Unless you have taken some time to look at it.
Take a look at this image and give it your best guess at a percentage disease?
What we need when measuring percentage disease is a fixed area - I really like a hula hoop for this - its easy to throw around on a green without doing any damage and you can throw it about enough for it to randomly settle in one place.
Next you need a set of disease markers - I've settled on a number of different size tiddlywinks but you could easily cut out some plastic into disease sized shapes.
You can then easily work out the area of both marker and HulaHoop to work out the %, if maths isn't your strong point then a quick google "work out area of a circle" comes up with a calculator.
We now have a fixed area and some fixed markers. I write on each one the % area that it is so I can quickly work out the total %.
Still with me? Good because in the above paragraph I've made something very simple sound more complex than it actually is.
Answer time:
4.11% were you close?
But that's only part of the story - in this case the spot I measured on was the worst impacted area of the green - and whilst there was disease elsewhere - this section was not representative of the whole green.
In order to come up with a figure for the whole green we need to start throwing the hoop. The more readings you take the more accurate it is. In this situation I took 5 readings.
0.2%
0.1%
1.6%
0.3%
0.8%
Average : 0.6%
This is a very quick, cheap and accurate way to measure disease area and quickly you can see that the standards we set ourselves are incredibly high.
In this situation we had a green with around 0.6% disease - yes 0.6% and still wanted to improve further.
It's a really worthwhile exercise when evaluating how effective your programme is and really comes into its own when you couple it with untreated control plots so you can assess the effectiveness of the treatment.
