"Even though most are not labeled as K fertilizer, it's there"

I recently received this inquiry:

"What is your approach to K fertility with regards to phosphite products? Even though most are not labeled as K fertilizer, it's there."

That's correct for products that include potassium phosphite. I'm not sure how all phosphite products are labeled. Here's how I answered:

"I would count the K in that type of phosphite product as a K fertilizer addition.

I would ignore the P from phosphite, not counting it as a P fertilizer addition."

For more about phosphite, I recommend Penn State's Understanding the phosphonate products.

The Winter's Tale

There are more surprising photos from Doug Soldat this week. Where potassium fertilizer was applied, there is more snow mold. Where potassium was not applied, there is less snow mold.

This photo, starting in the top right plot with the lowest amount of snow mold, and going clockwise, is:

  • top right, no K for six years
  • bottom right, no K for six years but high K added from August to October 2016
  • bottom left, high K for six years
  • top left, high K for six years but no K after August 2016.

It's not so surprising, actually.

Doug has been observing these results for some years now. See, for example:

Dog's footprint and grass susceptibility to this disease

I don't like turf diseases. If there is any fun in them, for me, it lies in only two things. First, is it a particularly well-named disease? Second, how awful are the symptoms?

I enjoy learning disease names and finding those that have the most interesting names. Nothing against brown patch and yellow patch, but those are pretty bland. Dollar spot is more interesting, and elephant's footprint even more so.

Then there are the symptoms. All turf diseases, if left unchecked, can make some hideous symptoms. In their standard form, however, I find some to be more hideous than others. Yellow patch, anthracnose, red thread -- often present, but sometimes only visible to those actually looking for symptoms. Compare to a disease like large patch, which in its standard manifestation is monstrous.

Using those criteria of interesting names and hideous symptoms, one of my favorite diseases is inu no ashiato -- dog's footprint. The name is interesting, and the symptoms are moderately hideous. I was glad to see this new article by Tomaso-Peterson et al. about Curvularia malina sp. nov. inciting a new disease of warm-season turfgrasses in the southeastern United States. From the introduction:

A foliar disease of these warm-season turfgrasses is often observed following prolonged or significant precipitation events such as tropical storms and hurricanes. The disease manifests as distinct chocolate brown to black spots (2–15 cm diam) that appear on Cynodon dactylon or Zoysia matrella putting greens, fairways, and tee boxes. Under high disease pressure the dark spots may coalesce to form large, irregular areas of blighted turfgrass.

"Is this the same as dog's footprint," I wondered?

A Curvularia leaf blight affecting Zoysia spp. in Japan, referred to as dog footprint, shares symptomology to that observed on C. dactylon and Z. matrella in the southeastern United States ... Based on these reports, our hypothesis is that the sterile fungus associated with Curvularia blight and causing similar symptoms in stands of C. dactylon and Z. matrella in the southeastern United States is a novel species of Curvularia.

The species was identified as Curvularia malina.

To date, C. dactylon and Z. matrella are the only golf course grasses from which C. malina has been isolated. Disease epidemics on Z. matrella appear to be more severe than on C. dactylon based on visual field observations. The disease is most prevalent in the spring and fall, which are normally characterized by moderate temperatures and ample precipitation. Symptoms may persist into the summer if prevailing environmental conditions remain favorable and the turfgrass experiences stress from intensive management practices.

So far so good. Dog's footprint is more severe on Z. matrella in Asia than on C. dactylon. However, in Asia the disease is most prevalent in summer, or in conditions characterized by warm temperatures and ample precipitation.

Based on the results of our research, C. malina induces disease symptoms in warm-season turfgrasses similar to those associated with Curvularia leaf blight.

It seems dog's footprint is caused by C. malina. Manilagrass (Zoysia matrella) can get lots of diseases, but in a tropical environment, this species is infected by few diseases, with the most common being dog's footprint.

Here is dog's footprint on manilagrass at Hilo in March.

This is at Okinawa in August.

This is at Manila in August.

This is at Shizuoka in July.

Those are pretty typical symptoms. And they are all on a monostand of one type of manilagrass.

I've noticed that some manilagrass varieties are often showing dog's footprint symptoms, and other varieties rarely do. I usually see this at two different locations in the same town. For example, lots of dog's footprint at site X, and then an hour later at site Y, a slightly different type of manilagrass has no dog's footprint.

Last July, I saw this at one location, on a golf course fairway with a mixed stand of different Z. matrella (korai) varieties and with some patches of C. dactylon.

On one variety of korai, lots of dog's footprint. On the Cynodon and other variety of korai, none.

This disease is ubiquitous on susceptible varieties in East and Southeast Asia. Finding varieties that are less susceptible seems quite possible.

Water quality and pesticide performance

This is a useful reference from Purdue Extension on water that goes into the spray tank. From the guide:

"Water often comprises ninety-five percent (or more) of the spray solution. What affect might it have on product performance? Research clearly shows that the quality of water used for spraying can affect how pesticides perform. Its effect on product efficacy is reflected in the success of your spray operation ...

Time spent addressing the quality of water used in the spray tank can pay big dividends. This publication provides an overview of water quality and related factors known to affect pesticide performance; testing methods and options to improve the quality of the water used are discussed."


I learned of this document when I read Megan Kennelly's post on nozzles and water quality.


Every spring when the snow melts ...

I look forward to some photos from Doug Soldat. For the past three years, he's had some fascinating photos to share of snow mold on creeping bentgrass. And each year, there was more snow mold where potassium fertilizer was applied, and less snow mold where potassium wasn't applied.

Spring of 2014

In the spring of 2014, there was more snow mold where K was applied.

Spring of 2015

Last year, there was also more snow mold where K was applied.

Spring of 2016

This year, it happened again. There was more snow mold where K was applied.

Doug will be talking about K in a TurfNet webinar in April: Is Your Potassium Program Hurting or Helping Your Turf?

On those creeping bentgrass plots in Wisconsin, adding K increases snow mold. No K had less snow mold.

At Rutgers, annual bluegrass plots deficient in K have had more anthracnose in summer and more winter injury. Eliminating the deficiency reduced those problems.

Then there is the MLSN guideline for K of 37 ppm. I recommend keeping the soil K above 37 ppm (Mehlich 3 extractant).

And there are hundreds of other studies about K. Some show a benefit from adding K, and some don't. I haven't read all of them, but I have read a lot of them. This sounds like it could be pretty complicated.

Actually, I don't think it is. Here's what seems to be the case, for both warm-season and cool-season grasses:

Ensuring the grass is supplied with all the K it can use will provide all the benefits associated with K. Adding more than that usually has no effect, other than wasting time and money, but sometimes has a negative effect.

As a turfgrass manager, all one has to do is ensure the grass is supplied with all the K it can use. This can be accomplished in 2 ways. One is by keeping the soil K above the MLSN guideline. A second is by applying N:K in a 2:1 ratio for cool-season grasses, a 1:1 ratio for seashore paspalum, and a 3:2 ratio for other warm-season grasses. I wrote about that in the final chapter of A Short Grammar of Greenkeeping and in The (New) Fundamentals of Turfgrass Nutrition.

Note that I do not recommend tissue testing for K (or any other element).

If you want to read more about K specifically, and about how the benefits of K come from correcting a deficiency, I recommend:

'Tis the season

Autumn is when one can find one of my favorite turf diseases -- elephant's footprint. Or at least this is my favorite name for a turf disease. It is found most often on unmown Zoysia japonica.

Al Bancroft shared a photo last week of what looks like early development of elephant's footprint.

 This is what the classic symptoms look like, further into autumn:


I was also reminded this week that real elephant footprints can be a turf problem too:

That's in Tamil Nadu, where one must beware of elephants.



For more about real elephant footprints on turf, see this turfgrass mystery.

N & MLSN: what's the connection?

We'll get to the N below. But wow! I didn't know silica was such a hot topic! After writing a few days ago (original post here) about silica and green speed, and how it doesn't make sense to me that silica application could increase green speed, there was quite a response, by e-mail, at this discussion on Facebook, and at this discussion on Twitter.

Application of granular silicon dioxide to a creeping bentgrass putting green in Japan

Korai (Zoysia matrella) greens are notorious for the high silica content of their leaves, but they are not noted for being exceptionally fast. Except when they are dormant. The idea that leaves with more turgor pressure, or leaves with more silica, could somehow be faster, still doesn't make sense. If that were the case, actively growing korai greens would be faster than dormant korai. Fortunately, data on green speed are easy to obtain, so if silica application really does increase green speed, someone should be able to measure it.

Bermudagrass thrives in a rootzone composed primarily of silicon dioxide

Jason Hooper sees the benefit not as something to increase green speed, but from silica application for plant defense against pests:

Continuing that discussion, I pointed out (with the help of John Dempsey) that silica application (in this case, calcium silicate) can also cause a dramatic increase in turf disease, especially with brown patch. So although I think Si application to turf is something worth investigating, and because the reported results are so divergent, Si is something that especially calls for a check plot.

Jason pointed out that MLSN might not be all good either, and that with low levels of N, if that is what the MLSN guidelines were recommending, there could be increased disease too, particularly dollar spot and anthracnose:

I want to explain that now, because grass with low N in the leaves is more prone to dollar spot or anthracnose -- when the other conditions are right for those diseases.

But the MLSN guidelines don't include N. The MLSN guidelines are for the macronutrients K and P and for the secondary nutrients Ca, Mg, and S. There is no MLSN guideline for N, and none for the micronutrients (for more about why there are no MLSN guidelines for micronutrients, see this).

Selection_056There are two parts to my explanation.

First, the MLSN guidelines don't include a recommendation for N. When I talk about N, I explain it like this. Adding more N makes the grass grow faster, and reducing N supply results in grass that grows slower. One of the (maybe the most important) most important tasks for the turfgrass manager is to control the growth rate of the grass. The optimum growth rate is to grow just enough to recover from traffic damage. The optimum growth rate is very site specific.

Turfgrass managers will generally choose the nitrogen application rate based on three things. They will look at the color of the grass and decide whether they want it to be the same, greener, or less green in the future. They will check the growth rate of the grass, and also consider whether that current growth rate should be adjusted. And they will consider the way N has been applied in the past, what the results of those applications were, and incorporate that knowledge, and an assessment of the current turf conditions and weather and weather forecast, to consider if the amount and source of N applied in the past should be applied again, or if it should be adjusted.

This is not part of MLSN, but I suggest it can be added to those three things. The temperature-based growth potential of PACE Turf can be an excellent site-specific predictor of how much N the grass may use at different times of the year. That information can be added to the color, growth rate, and experience to help choose the optimum N application rate. To try it out, the climate appraisal form from PACE Turf has all the equations embedded. You can input temperature, grass type, and maximum N rates for your site to see how this works.


To reiterate, N recommendations are not part of MLSN. The turfgrass manager decides what growth rate is desired at the facility, and chooses the N rate by whatever method desired.

Second -- and this is where N supply and MLSN fertilizer recommendations are connected -- when I calculate a K, P, Ca, Mg, or S recommendation based on soil test results and the MLSN guidelines, I will consider how much N is applied at that location. This is part of the a + b - c approach that I explained in this presentation. How do I integrate N?

a is the amount of an element the grass uses. That is where N comes in. b is the MLSN guideline, nothing to do with N. c is the Mehlich 3 soil test result for an element, nothing to do with N.

To estimate a, I recognize that when more N is applied, the grass is going to grow more. As it grows more, the quantity of nutrients harvested from the soil are more. Thus, the fertilizer recommendation for an element increases the more N is applied.

One of the fundamental questions I ask about any turfgrass management practice is why are we doing this? I'm glad Jason is questioning MLSN. Question everything! In this case, however, I don't see that there is any connection between MLSN, N, and increased potential for disease.

Frankly Speaking about turfgrass nutrition, the MLSN guidelines, & the GSS on TurfNet RADIO

Check Out Science Podcasts at Blog Talk Radio with TurfNet RADIO on BlogTalkRadio

I had a chance to talk with Frank Rossi tonight on TurfNet RADIO. We discussed turfgrass nutrition, soil testing, the MLSN guidelines, the Global Soil Survey (GSS), and not much else. But Dr. Rossi has a way of asking interesting questions, and I tried my best to answer them in a way that makes sense. Have a listen to our discussion and see if we succeeded!

For more information about the things we discussed, here are direct links:

"This publication is intended for professional turfgrass managers who use fungicides as part of an overall disease-control program"

Selection_009"This publication" is Chemical Control of Turfgrass Diseases 2015 by Paul Vincelli and Gregg Munshaw. A wealth of information about diseases is packed into only 24 pages.

And it is not just about chemical control. Common turfgrass diseases are described, the environment and season in which the disease is most likely to occur are explained, and the best control measures for each disease are given. There are also informative sections about fungicide resistance, improving spray efficacy, detrimental effects of pesticides, and much more. This is a guide that will be of use to every professional turfgrass manager.

Diagnosing Turfgrass Diseases

Jim Kerns has written this post on accurate disease diagnosis at Turf Diseases. You'll want to read the whole post – it is really good, and useful not only in understanding disease diagnosis but also in understanding diseases so they can be avoided or controlled more effectively. Here are a couple excerpts:

Golf course superintendents are forced to manage their plants on the brink of death to ensure firm, fast playing conditions. When managed on the precipice of death, many times turf falls off the edge and succumbs to decline. The golf course superintendent then must determine if a disease or some other factor is killing their turf. In this situation it is always easiest to assume a disease is causing the problem, however many times a biotic entity is not the cause of decline. Over the past 8 years, our Turfgrass Disease Diagnostic Lab has received approximately 4,000 samples. Of those samples 30 to 50% do not have the appropriate characteristics of a plant disease.

That's interesting. Almost half the samples submitted to the diagnostic lab do not have appropriate characteristics of a disease. 

This bermudagrass green in Southeast Asia was thought to have disease; I assess this as mechanical damage rather than decline caused by any fungal pathogen

And when sending a sample to a lab for diagnosis, are photos useful, and if so, just what type of photo should be taken?

Photos are an excellent addition to any submission. They clearly show what stand symptoms are present and the pattern of development. We suggest only taking pictures from a distance, we typically find that close-up images are not useful.

This is something quite interesting too, that pathogens are in almost every sample, even in healthy turf. 

Turfgrass pathogens are ubiquitous in nature. Turfgrass systems produce a lot of carbon and are excellent environments for microbes. In many cases we see multiple plant pathogens in a given sample. Yet we do not report all the organisms we find. For example, in almost every sample we receive significant amounts of dark, ectotrophic fungi are characteristic of take-all patch or summer patch are present on roots. Again coming back to the diagnosis triangle, diagnosing a disease is more than simply finding a plant pathogen. A disease is an abnormality in structure or function of plant due to the continuous irritation of plant pathogen, therefore it is important to realize that pathogen does not equal disease. In my humble opinion, receiving a report listing plant pathogens is not an accurate disease diagnosis.

In many cases, especially with warm-season turf during times of active growth, one sees very few diseases even though pathogens are still present.

Warm-season turf at the Asian Turfgrass Center research facility was never treated with fungicides to control turf diseases because cultural management practices such as mowing, irrigation, and fertilizer could be adjusted to manage any pathogens

If you have a turfgrass disease problem, this list of turf diagnostic labs from PACE Turf will help you find a suitable place to send a sample.