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.

Impact of nitrogen sources on spring dead spot

In a post earlier this spring, I briefly mentioned our recent findings on the impact of nitrogen sources on spring dead spot development in bermudagrass turf. I am preparing to present this research at the upcoming American Phytopathological Society Meetings in Portland, OR and thought I would provide everyone with a sneak peek of our findings.

Most turf managers in the southeast and midwest are all too familiar with spring dead spot. However, in light of the results below, it is important to realize that the disease is caused by three different species: Ophiosphaerella herpotricha, O. korrae, and O. narmari. The most common species in the southeastern US is O. korrae, whereas O. herpotricha is prevalent in the midwestern US. If you are unsure of which species you have, ask your friendly neighborhood turf pathologist to find out which species is most common in your area.

We initiated this research in 2004 to determine how fertilization programs influence these different spring dead spot species. Each plot was inoculated with O. korrae and O. herpotricha in Fall 2004, fertilization treatments were initiated in May 2006, and were continued through 2007 and 2008.

Some of the main findings of this research are as follows:

1. Spring dead spot caused by O. herpotricha was suppressed very effectively in all 3 years by fertilization with ammonium sulfate. Sulfur coated urea provided some control in 2008, and calcium nitrate provided moderate suppression in 2009.
2. Ammonium sulfate had no effect whatsoever on spring dead spot caused by O. korrae. Instead, calcium nitrate provided almost complete control of this species in all 3 years.
3. Fall applications of potassium, dolomitic lime, gypsum, or elemental sulfur had no effect on either spring dead spot pathogen.

What does this mean? We are unsure at this time if the observed spring dead spot suppression is due to changes in soil pH or other nutritional effects. For example, suppression of O. korrae by caclium nitrate may be due to higher soil pH or increased calcium availability. Regardless, if you have struggled with spring dead spot in the past, take a look at the nitrogen source you've been using and consider a change to either calcium nitrate or ammonium sulfate.

Many turf managers apply potassium in the fall, as this has been thought to help reduce spring dead spot development. During the three years of this study, we saw no benefit from fall applications of potassium or other nutrients. It is important to point out, however, that we applied 2.7 lbs K/1000 sq ft from potassium chloride (0-0-60) during the summer in conjunction with our nitrogen applications. Therefore, as long as adequate amounts of potassium are applied during the season, additional fall applications do not appear to influence spring dead spot development.

It's a Mix Out There!

With all of the wacky weather we've had in California, we're seeing a mix of spring and summer diseases in the lab here and through reports from superintendents.
Rapid blight and Waitea are still active on Poa greens as is pink snow mold here and there in Northern California.

Anthracnose still hasn't shown up from Poa greens just yet - but has been seen on stressed perennial ryegrass samples from roughs and on a bentgrass green in Idaho.

In this bentgrass case - low fertility contributed to the disease popping up on mechanically or weather damaged turf.

Bermudagrass samples are starting to show up in the lab with decline or other ETRI on the roots. As we get further into the summer transition to bermudagrass, superintendents are starting to see weak areas thinned out by pathogen activity on the roots over the winter. A healthy dose of sun, heat and water will probably get thinned out areas of bermudagrass to fill in, but take note of these areas and see if you can improve compaction, fertility or drainage here; environmental factors that usually contribute to decline, spring dead spot or ETRI damage on bermudagrass.

It's all about your roots: good roots now means less summer stress later
Already, we've been getting samples in the lab showing heat and summer stress. With rapid changes in weather and conditions, greens can go from looking good to looking like crap in a very short period of time. Often the first heat spell will show where you have good roots. The more roots you can put down before the summer heat starts the better. That means additional solid tine aerification, addressing dry spots will handwatering or soil wetting agents and most importantly, adequate nitrogen fertility. Poa/bent greens need at least a quarter pound of nitrogen per 1,000 sq ft/month and even up to half a pound if you have a lot of play or traffic. Give cool season turf enough food to grow now, because when we start going into the 90s and 100s, cool season turf will start to shut down and you may be in trouble if you don't have enough roots or plant mass to make it through the summer.

Watching and Waiting

Well things in the Midwest are starting to appear "normal". We have had quite the weather the past few weeks, with severe winds and significant rainfall. There is very little to report from the Upper Midwest. Most golf courses are on the road to recovery from any winter kill, however there are still some spots here and there.

As I mentioned, the spring storms have been severe and many golf course superintendents find themselves working on tree clean-up. Not much in the way of disease activity in the Midwest. We've had a few reports of yellow patch, leaf spot and dollar spot in Mid to Southern Illinois, but nothing major yet.

However, this is the perfect time for take-all patch and fairy ring preventative applications. Soil temperatures at a Madison, WI golf course were 57F on Tuesday morning. Now is also the time to monitor nitrogen fertility levels if you have a significant stand of Poa annua. Poa has started to seed at a few golf courses and with that expenditure of energy those plants may need some nitrogen. If the plants start to look chlorotic, than a light foliar feeding may be necessary. This has been shown to reduce anthracnose severity by Dr. Bruce Clarke's group at Rutgers University in New Jersery.