Turfgrass Speedo is Better Than I Thought

Last fall I came up with the idea of comparing actual growth to ideal growth to get a ratio of growth. I called this tool the turfgrass speedo.

Ideal growth was calculated using the growth potential formula on my weather modeler spreadsheet and would use the ideal monthly nitrogen rate to determine how much grass should be harvested based on actual conditions not just a date on the calendar. The idea was to growth the grass at the right speed, not just as slow as possible. Growing the grass too slow is worse than growing it too fast. When you grow it too fast you get excess thatch and have to mow it more but when you grow it too slow it can't handle the traffic or stress of any kind really.

I had made all sorts of observations about growth in the past and the model seemed good. This winter I started a new job at a new course and was excited to see how the model worked at a different course.

For the first 5 months of the year the model was working perfectly. It suggested growth was too high when it was actually too high and during March through May it was predicting growth almost perfectly.

This has to be a coincidence but my turfgrass speedo is almost bang on for predicting yield this past week and month 🤷‍♂️ scary close pic.twitter.com/xarpoZPUy3

— Jason Haines (@PenderSuper) March 21, 2019

When June hit the growth rates seemed to be OK but the speedo suggested that growth was too low for the weather we werre having. I wondered if the model wasn't that good because the greens were awesome. Green speeds were way up and golfers were happy.

I noticed the first incidence of anthracnose on June 25th and we sprayed for it shortly afterwards. I wasn't going to get fancy my first year at a new course.

Anthracnose came on hard in late June, got better in July, but again, got much worse in August.

The disease slowly progressed in July and we increased nitrogen rates to help manage the disease as this is usually the most effective way of managing anthracnose. As July was quite cool, growth rates were down and nutrient demand was also low. The only problem was that in August the disease got worse and the speedo again suggested that growth rates were way below where they should be. The charts showing nitrogen applied vs nitrogen removed via clippings also showed that we weren't getting very good return on our fertilizer applications. I would have expected much more growth for the amount of fertilizer I had applied.

I would remove about 80% of the nitrogen that I applied in the clippings at Pender Harbour

My new course wasn't getting a very good clipping return, only 20%

Maybe the models were wrong I thought.

So we kept on fertilizing and the disease kept on getting worse. The bentgrass that was seeded a few years ago was very happy, but the predominantly poa greens were not doing so good. The anthracnose was bad and we couldn't get the growth we needed and as we all know, fungicides aren't the ideal solution for diseases like anthracnose.

I had had enough so applied a very heavy nitrogen application to the worst greens to try and push recovery. They greened up but growth didn't spike at all. I then applied a phosphite product to the greens and the day after they looked the worst I had seen all year. BINGO!

It's common knowledge (or should be if you are using these products) that applying phosphite to phosphorus deficient turf will make that deficiency worse. Our soils tests were high in phosphorus but what my observations and the data were suggesting is that something was limiting growth and now I knew that it was probably phosphorus. I applied some fertilizer containing phosphorus and the day after the greens looked the best they had looked in more than a month.

Severely affected green is glowing the day after a phosphorus application

Growth rates have climbed substantially and the models are happy once again. We are still on the low side of the ideal growth and have to push recovery so the plan is to continue to push growth until we are on the upper side of the growth ratio.

Overall growth rates have been too low this year but have improved in the past week to ideal levels.

Why wasn't the poa getting enough P? I don't know for sure but the roots were pretty short and the maybe they weren't as deep as the soil tests in the past were taken from. This would also explain why I had OK growth when temperatures were low but as soon as the demand went up, the grass ran out. We had a rough winter and maybe that was why? The spring was super dry and hot so maybe that's why?

We are getting a much better nitrogen return this past week as conditions improve.

This was a first for me. Normally growth rates were too high in the summer months and I always got an almost immediate response to nitrogen fertilizer.

So lesson learned and now I know that the models are probably better than I think. Using clipping volume and weather data can show you when you are within normal conditions and could probably give you an early warning that something isn't right. It's difficult to judge what amount of growth is appropriate for the ever changing weather we experience so models like this can make fertilizer decisions easier and can probably point out potential issues sooner.

My previous course had the opposite problem. The newly established and deeply rooted bentgrass would grow out of control in the summer as it had so many nutrients available the the poa NEVER had access to in the soil.

It's super easy and inexpensive to simply apply a complete fertilizer blend each week especially during the stressful summer months. When growth rates drop off maybe rely more on what the soil can provide. Or, if you have more bentgrass, use this phenomenon to kill poa. Unfortunately for me, there is a lot more poa than I would like here so that kind of craziness needs to wait a few more years.