Tuesday, 24 September 2013

Quantifying OM Release and Integration Into IPM Program

As things wind down for the season I begin to have time to reflect on the past season and make sense of some of the data I have collected. This season wasn't without it's challenges especially when it comes to disease management without the use of traditional pesticides. Obviously I wasn't successful but I made some important observations that should help me next year.

 I had an amazingly successful winter but it all came crashing down in June. I again had a very successful July and August but again in early September I was hit hard with fusarium. June and September have always been tough months as they are transition months, they are warm but also usually wet. This creates the perfect storm for fungal attack. Without an effective organic contact pesticide I was out of luck.

It is pretty well known that high nitrogen generally means higher incidence of fusarium on putting greens. It wasn't until I came across the GP fertility method that I was able to more accurately determine the actual nitrogen needs of the plant. Basically what this helped me determine was nitrogen application timing, something that was more or less a mystery to me until last summer. I knew that the total amount of nitrogen applied was a factor in disease development but felt that the timing also played an important role.

In recent readings I came across something about nitrogen release from soil organic matter and this got me thinking about how I have been trying to use nitrogen to control M.nivale on my putting greens. All along I had been completely ignoring the amount of nitrogen released from OM (organic matter) in the soil. Obviously this would have a huge impact on plant health but I had no way of determining how much was being released at any given time. I actually still don't have a good way of knowing but I have come up with a way that I can very roughly estimate what might be happening in there. When I say rough I mean the worst dirt road in the deepest darkest corner of Siberia rough. Ugly rough.

So most if not all of the research I have used to determine nitrogen rates to discourage fusarium have not taken into account soil OM levels. It's probably safe to assume that OM levels in a lot of studies are rather low as the study greens are often not that old. Either way the amount of N released from the study root zones is probably similar to what I am experiencing but there is obviously no way to know. So using rates determined from studies is sill a good idea I just think that there is more to be known regarding nitrogen application timing and when OM nitrogen release occurs.

So that basis of my OM release estimation comes from a formula where;

amount of N released from OM /1000 sq ft per year =  1.7 * ln(OM%) + 1.8 per year

Larry from PACE Turf was kind enough to show me this formula but cautioned that it was a " VERY VERY ROUGH GUESS."

As I have about 1.7% OM in my putting green rootzones which gave me about 2.7 Lbs N/1000 sq ft or to put that in a measurement system that makes sense about 1.22 KG N per 100m2! HOLY SMOKES!! That's more nitrogen from OM that I apply using fertilizer but it doesn't at all mean that I should stop applying fertilizer. After all this OM release has been happening forever but it's just not something that I have quantified yet.

For IPM and specifically managing for M. nivale it's not just about total amount of N applied per season but I'm thinking it's more about the timing of those applications. As of now, I don't have a way of determining how much N is released from the soil OM levels at any given moment but I can use this rough seasonal estimation to make a further rough estimation based on a growth model I already use. You guessed it, GP (growth potential).

Now the release of N from soil OM is going to be dependant on a lot of things, not just temperature. To be fair, so is the growth of a plant. We got air temperature, soil temperature, humidity, soil type, soil air, soil moisture, amount of light the list goes on. The growth potential model is just a basic way of trying to understand the complex way nature works based on temperature, it's the best we got OK. If you really think about it though, most of the biological activity is based on temperature as we are pretty good at controlling all other environmental aspects of the growing environment.

So lets assume that the release of N from soil OM closely mimics the N requirements of a plant after all the N requirements are based on biological activity. The GP formula gives me theoretical monthly N requirements which can be added up for a total yearly N requirement of about 1.1Kg N/100m2 per season in my climate. I can then take the monthly requirements and divide them by the yearly requirement which gives me a month % of total. I can then reverse the formula using this percentage and the theoretical OM N release and this gives me the theoretical N release from OM per month based on temperature...... or something.

Now please before I go on, this is more than likely all a pile of garbage, I'm just speculating here, as usual.

So the above chart shows the amount of N added using GP (blue), the theoretical amount of N added from OM (red), and the total amount of N being added to the system (orange).

Now I should be able to use this data to compare nitrogen rates with disease pressure. Simply put the months of June and September are hell. May wasn't that bad and neither was October. The total N being added to the system in May is about 0.23 Kg N/100m2 and October sees about half of that. The total amount of N being applied to the system in June jumps to 0.4Kg N/100m2 or almost double. This could be a bid deal especially if the environmental conditions are still favourable for fusarium development.

June 2013. Look familiar anyone?
So what do I do? At this point I'm not totally sure what the best answer is. If you look at the OM N release from June is just about what the combined total is for May. Should I just not apply N in June!?! I don't think that's a good idea. Maybe I apply 50% of the required N, or 75%. What if I skip fertilizer applications if the weather is ideal for OM N release and fusarium. Both of the major disease outbreaks followed periods of warm weather and intense precipitation, followed by needle tine aeration to get air back into the soil profile. Whamo, we kick microbial action into turbo and the moisture and lack of drying sun makes disease outbreak explode.

Since I'm being so half assed and guessy here I could just assume that the amount of N release is exactly the same as the GP theoretical N requirement. If disease pressure is high I better keep rates less than 0.23 Kg N/100m2 per month. They say rates above 2 Kg N/100m2 per season significantly increase fusarium activity so why can't I say that rates higher than 0.23 Kg N/100m2 per month or 0.06kg N/100m2 per week significantly increase disease activity. Half that number for amount of N actually added as fertilizer! Those are pretty low rates.

I could speculate further that the reason guys who use "biostimulant" products or amino acids for plant health is because they for once aren't apply too much nitrogen.

In the end I could be totally wrong about the relationship with N and fusarium but at this point it's the best I can come up with and something that I have had the most success with so far. I now have all winter to think about this and try to come up with more crazy theories and ideas of how to survive June and September without traditional pesticides. If you got a better way to determine N release from OM based on something measurable I would love to hear about it!

Monday, 23 September 2013

Summer Dollar Spot Success

It has been almost 2 months since my last post and it's not because nothing has been happening. It was a really busy and good summer and I was trying some new things out to combat disease on the golf course. Since my last disease update the main disease of focus has been Dollar Spot.

Last year I was successful in combating Dollar Spot on my greens but my fairways were wiped out. It was the worst I had ever seen actually. As always applying a fungicide to my fairways wasn't possible.
You could see the devastation from space

More disease than grass in 2012
I accounted this extreme disease to a few factors.
  • In an attempt to drive down fertilizer use on my fairways I had got to 100% UMAXX slow release nitrogen source. This allowed me to put down a heavier granular rate that would last longer. In theory I could get by with just two applications per year and would half the amount of nitrogen on my fairways. With the tools I had at the time this seemed to be the most realistic way to drive down fertilizer use on my fairways as I didn't have a good sprayer.
  • My fertilizer application timing was a bit off causing my nitrogen source to lean out too much in mid summer something I later learned wasn't appropriate for my climate.
  • I had dried the fairways out and without the use of a wetting agent it was hard to re-wet them with my ancient irrigation system. Dry soil isn't good for getting nutrients into the plant I learned.
In the past there really wasn't much I could do for Dollar Spot other than apply a lot of granular fertilizer and sweep dew which was costly. This year I decided to try something new on my fairways.  This winter I got an almost entirely new equipment fleet which included a Toro Workman 200 Spray system mounted on a 4wd diesel workman. The 4wd was a must as the fairways here are very very steep. This new sprayer opened up a lot of possibilities for me. Instantly I could spray fairways in a few short hours with whatever my heart desired.

4wd is a must on steep fairways
Right away I threw wetting agents into my fairway program. I used Dispatch as it was the most economical. I wasn't looking for a miracle, just anything better than nothing! Next I was going to melt down UMAXX and apply it at the same time as the wetting agents. After some discussion on Twitter I was convinced to go with straight urea as it was cheaper and other superintendents had noticed no significant changes between the two nitrogen sources at a 3 week application interval. The use of urea also allowed me to more accurately follow the growth potential model on my fairways than if I was to use a slow release nitrogen source. The soluble nature also increased the likelihood that the nutrient would get into the plant. I have to say I was not disappointed!

This plan took on the disease on a number of preventative fronts, primarily giving the plant what it needed when it needed it. The wetting agents allowed me to keep the soils relatively moist but not too wet which kept the nutrient supply to the plant more consistent. The soluble nitrogen was also quickly taken up by the plant and the relatively frequent applications kept the supply consistent. I also decided to go with a light a frequent irrigation regime to try and keep soil moisture as consistent as was possible with a terrible soil.

A quick aside about using straight urea. I know there are a lot of apparent reasons why urea is bad (volitization, burn potential, it's not organic, growth surge, blah blah blah) but I have to say my experience this summer was nothing but fantastic. Science has shown that urea is quickly taken into the plant and in turf volatilization is of little concern. It is considered one of the best nitrogen sources available. In my experience this summer I did not have any apparent issues with nitrogen losses. I had a good consistent feed all summer long even with low rates of 0.12kg N/100m2 on a 3 week interval in July and August. Growth surges were more dependant on rain and temperature than anything else. I would try and apply before a rain to wash the urea and wetting agent into the soil but a few times I had to use the irrigation system with no issues. Mixing th urea was also very easy. I would just pour the bag of low grade urea into the basket on the sprayer and it would melt as fast as I could fill the tank. Best of all was the cost. With a cost of less than $120/ha/ season to fertilize fairways I was a happy camper! If you get Ag grade it's about half the price as "greens grade" and melts just as good. In some areas it's also tax free wink wink.
The only picture worthy incidence of dollar spot on the course this
summer was on the 4th approach for a few days

So now that we are safely out of Dollar Spot season I can say that this plan was an astounding success. My fairways have never been better actually. Of course there was the odd incidence of disease this summer but they were minor. One of my approaches was particularly hard hit as a wet spot prevented me from taking my sprayer on it. My tees were also hit with a bit of the disease but I attribute this to the use of slow release N. Next year it's straight urea on them too!  I think this program will also benefit my winter disease management plan on fairways. With less available nitrogen going into winter I hope to see a reduced incidence of Fusarium Patch. Time will tell on that one...

I wish all disease management approaches were this good. Improved conditions, less disease and significantly less cost! (other than a brand new sprayer of course) There are a few things that I will do differently next year but they don't relate to dollar spot and will be the focus of my next blog post looking back on an entire season of growth potential fertility.