Disease population growth

44985081_412851935918660_5215788497348067328_nThe last few weeks I’ve been on the road presenting my “Fungicide planning presentation”.  The core message has been slightly simpler than “planning” though. In an attempt to try to understand the way to get the best out of fungicides I think it’s imperative we

dr dunderstand the way that the disease develops. This 2008 article by Dr Danneberger got me thinking about this concept.    During periods when conditions aren’t conducive to disease development the disease will sit quietly in the fibrous layer near the surface in Conidia form waiting for the right conditions:

  • Mild
  • Damp
  • Humidity
  • Lush growth

When these conditions arrive the impact isn’t instant. The process from the Conidia germination to population levels being high enough to make disease visible takes a while.  The key message here is whilst the conditions are conducive to Microdochium development it will take a while for the disease to become visible.  Everyday waited means a higher population of disease you’re asking a fungicide to deal with.

AI chart
This chart shows the reduction of quantities of Active ingredient per Ha over the last 25 year

Modern pesticides have much lower quantities of active ingredient than their predecessors although their mode of actions are far more effective at reducing disease populations when applied earlier.

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I did an experiment earlier in the year and took a plug from a green in Early August and in an attempt to accelerate disease I placed it in a plastic bag with some moisture. This kept the plug in a constant high pressure situation. I was surprised to see that it took 7 days for the plug to develop any signs of disease, however once it started the disease spread rapidly.

This ties in really well with the exponential growth theory, whilst in the Autumn we’re generally studying our greens looking for disease because we know the conditions are right, however we won’t see any visible signs until the disease population has got to a point where it can cause damage. The speed this happens will vary dependent on many factors, including:

  • Moisture on leaf
  • Temperature
  • Historical disease pressure
  • Fibre content
  • Grass species

By using forecasted weather to help us decide when to apply fungicides we can pull applications forward by a few days which will have a dramatic impact on the success rate of the fungicide.

A cold snap in the weather like the one we’re getting at the moment is fantastic as it will halt that disease population increasing, if it’s under some kind of fungicide protection then it will also increase its longevity.

Key message: A planned approach to fungicide applications which is then altered based on a forecast rather than waiting for visible symptoms will have a greater impact. 

During my presentations I try to separate out the effects of Integrated Turf Management and Fungicides. I believe that they are doing separate jobs. I’ll go into that in my next blog

 

 

 

 

 

 

 

 

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