Are your greens yellow?

During this time of year, many golf course superintendents report yellowing of creeping bentgrass greens in spots, patches, or irregular areas. While there are a few different diseases and conditions than can cause these symptoms, many assume that “yellow tuft” is to blame. In fact, yellow tuft is not very common in the Southeastern US, and typically only occurs on poorly drained greens or during very wet weather.

A misdiagnosis of yellow tuft can be costly. Few fungicides are labeled for this disease, and those that are have no activity on the other problems that cause yellowing in bentgrass greens. Here’s a description of a few of these “yellow” problems seen on bentgrass greens and recommendations for their management:

Yellow Tuft

Above-ground symptoms of yellow tuft appear in small spots, typically 1 inch in diameter or less. In severe cases, the spots may merge to create irregular areas of yellow turf. Close examination of these spots will reveal that the turf is slightly raised above the canopy. Carefully remove one of these spots from the turf using a knife or ballmark tool, and you will see a massive number of tillers emanating from a single node. This “witch’s broom” symptom is a key characteristic of yellow tuft.

Yellow tuft can cause damage to the turf if left unmanaged. Most of the damage is a result of scalping injury as the infected tillers are pushed upward above the height of cut.

Yellow tuft is caused by a Pythium-like organism called Sclerophthora macrospora. This pathogen infected the crowns and leaf sheaths of the turf. Once established, the pathogen induces excessive production of hormones, which leads causes the excessive tillering.

At this time, the Pythium fungicides mefanoxam and fosetyl-Al are the only fungicides labeled for yellow tuft control. Based on our experience, fosetyl-Al is not very effective, so stick with mefanoxam for preventive or curative applications.

If you have chronic problems with yellow tuft, poor drainage is likely to blame. Taking steps to improve surface or subsurface drainage will eliminate or reduce the problem and save lots of money in fungicides over the long term.

Yellow Spot

In my experience, this is the most common cause of yellow symptoms on bentgrass greens in the Southeast. Symptoms of yellow spot are very similar to yellow tuft, but the spots can be much larger, up to 4 inches in diameter. In addition, the growth habit of the turf is completely normal: it will not be raised above the canopy and no excessive tillering is observed.

Unlike yellow tuft, yellow spot never actually causes damage to the turf. However, due to its aesthetic effect and perceived effect on the consistency of the playing surface, it still warrants management.

We are still not sure what causes yellow spot. We have consistently seen certain types of blue-green algae (cyanobacteria) in the spots, and we theorize that they are producing toxins that induce the yellowing symptom. Other scientists have not been able to establish this same relationship, so the true cause remains unknown.

Nevertheless, we have seen very effective control of yellow spot from applications of chlorothalonil. Applications of 2.7 oz a.i. per 1000 ft2 every 14 days have typically provided good prevention, but higher rates and shorter intervals are needed for curative suppression. In addition, yellow spot tends to be more severe when fertility levels are low and the turf is subjected to frequent drought stress.

Etiolated Tiller Syndrome (ETS)

This is the least well understood of all of the problems that cause yellowing, but has been observed with increasing frequency over the last five years. ETS is easily distinguished from yellow spot and yellow tuft. ETS typically develops in irregular areas, but sometimes it can appear in patches coinciding with bentgrass clones. The key characteristic is that the youngest leaves in affected areas will be etiolated, or elongated and yellow in color. At first the rest of the plant will appear normal, and no increased tillering is evident as with yellow tuft. Some turf decline can occur if turf affected by ETS is subjected to heat or drought stress.

We still have no idea what causes ETS. There are plenty of theories, but no hard facts. Most cases we’ve observed have been associated with combinations of plant growth regulators and various biostimulants containing giberellic acid or cytokinins. Then again, there are a few cases where neither was applied.

If you are having problems with ETS, take a look at what you are applying to the greens. If you are applying plant growth regulators and biostimulants, try deleting one or the other out of your program. This may alleviate or eliminate the problem.

Nitrogen Deficiency

The most frequent cause of yellowing in putting greens is nitrogen deficiency. Typically, nitrogen deficiency appears uniformly across entire putting greens, but sometimes it can have a patchy appearance, especially on older greens, due to the responses of different bentgrass genotypes in the population. Any time you see yellowing, take a look at your recent fertility practices and have a tissue sample analyzed for nutrient content to determine if nitrogen or other nutrients are limiting.

Can herbicides impact diseases?

Next week starts with another International Turfgrass Research Conference. Every four years, turfgrass researchers from across the world gather to discuss the latest information about managing all different types of turf. For my part, I am presenting on two of my favorite interests in turfgrass research...weeds and diseases.

Sometimes research results throw up on you (makes me think of poor old Watson this past weekend...heartbreaker at Turnberry) and present you with some serendipitous findings. This holds true for a variety of fields, but the interactions among plant growth regulators or herbicides and turfgrass diseases in particular can be great.

The first thing that comes to my mind is the reduction of dollar spot from applications of the plant growth regulators Trimmit or Cutless. Due to direct fungistatic effects, these PGRs can result in a reduction in the disease. In our most recent study, the combination of Trimmit + Emerald OR Banner MAXX improved disease control when compared to the fungicide alone and resulted in a savings of a fungicide application over the course of the season. In these economic times, a reduction of a single fairway fungicide application can result in a significant savings.

OK, back to my original point...the conference in Chile.

On Monday (during my next post), I will be giving a presentation on a relatively new herbicide used to control annual bluegrass. Velocity, gaining momentum in the Northeast, can effectively be used to suppress annual bluegrass in bentgrass fairways. While it is labeled for creeping bentgrass, its impact on other bentgrass species (colonial in particular) was unknown. In trials at UConn, we found that applications of the herbicide can result in an increase in brown patch. This may be a particular problem since Velocity is most effective when applied in the middle of summer which is typically the time when brown patch becomes active (To the contrary, Velocity has been shown in other studies to actually reduce dollar spot). Unpublished results also indicate that the increase in disease holds true with tall fescue too.

In the photo above, the untreated plot (center) was virtually disease free while the plot treated with three applications of Velocity (left) was severely infested by the brown patch pathogen.

Although we have not researched it yet, my guess is that fungicides typically used to suppress brown patch would likely minimize any negative effects of the herbicide. With the varying agronomic practices put into place at any one time on a golf course, superintendents should consider how one factor may have unexpected negative (or positive) results.

*Photo credits to Alex Putman, former graduate student at the University of Connecticut

Is your turf juicing?

Last week, Manny Ramirez became the latest in a long line of baseball stars to be exposed as a cheater. When reports surfaced that he had failed a drug test, Manny resorted to the typical excuses: someone told me to take this stuff, I didn't know what was in it, I didn't know it was illegal, etc.

Yeah, right.

You might ask yourself, "How could a professional athlete, who earns a living with his body, take a drug or supplement without knowing what's in it, what side effects it has, or how it might interact with other supplements?"

It's a valid question, but it begs another question. If you make your living by growing healthy turf, why would you apply something to your greens without knowing exactly what's in it, what side effects it might have, and how it might interact with other management practices?

And yet, many golf course superintendents do just that by using biostimulants, turf enhancers, biofungicides, and other miscellaneous products. Many of these products have unknown ingredients, haven't been thoroughly researched, and are of questionable benefit. When you boil it down, they aren't any different from the plethora of diet supplements advertised on late night infomercials.

Before using these products, consider a couple of things. First, in many cases the positive response you see is nutritional. So why not apply fertilizers instead, so you can control how much of each nutrient is delivered? 

Second, some products contain plant growth hormones, which can negatively interact with your growth regulator, herbicide, or fungicide programs. It just doesn't make any sense to apply a gibberellic acid (GA) inhibitor like trinexapac-ethyl and then turn around and apply an unknown amount of GA from a biostimulant.

I am not saying that all biostimulants, turf enhancers, and biofungicides are bad. There are some good products out there that have their place. But I do encourage you to be an informed consumer by demanding to know exactly what nutrients and hormones are in the products you purchase, asking to see research data that shows the products are beneficial, and reviewing the research carefully to make sure it is relevant to your situation.

You wouldn't take a pill without knowing what's in it, don't ask your greens to do the same thing!