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We are testing a variety of plant growth regulator products and fungicide chemistries for efficacy on early spring seedhead control and possible disease reduction. This study is being conducted on a fairway mixed stand (50/50) of Poa annua and creeping bentgrass and has been initiated to show visual turf quality differentiation of the various products. Last season, test strips on a nursery green at North Shore Country Club in Glenview, IL showed considerably less disease when a plant growth regulator, Embark, was applied once during June. The early season applications as seen in the bar graph below for “Visual Quality” are at 21 and 28 days after treatments (DAT).

The first application was critically timed to coincide with forsythia bloom on April 14th. There are three Embark treatments all at the 40 oz/acre rate; Embark alone, Embark with Primo 0.125 fl oz/M and Embark with Primo 0.125 fl oz/M and also Signature 4 oz/M. This series of Embark treatments was only administered as a one time application due to a high amount of tip burn on the creeping bentgrass and chlorosis on the Poa annua. All treatments were within labeled rates. The result is poor visual quality of turf in this early spring period. However, all of the Embark treatments were excellent at eliminating all Poa annua seedheads (100% control).

Two combinations of Proxy and Primo (5 fl oz/M + 0.125/M) were tested, at a 21 day interval with one including Signature at the 4 oz/M rate. However, neither of the two mixes resulted in greater seedhead suppression than any Embark combination (see graph). The visual quality for the Proxy + Primo + Signature yielded better quality at both the 21DAT and 28DAT (7 days after second application), but interestingly, there was no statistical differences between the treatment that contained only Proxy + Primo and any of the Embark treatments.

So, the question that is brought to my attention from the data is whether there is some sort of synergistic effects in mixing Proxy + Primo + Signature? On the flipside, we don’t see any of these effects in tank mixing with Embark, so this means we can rule out that it may have had something to do with a pigmented spray or not. Secondly, will the sacrifice in early season turf quality using Embark pay off when we get to the heat of the summer? And lastly, is it worth the dollars to apply fungicide this early for dollar spot when we have very low disease pressure? Over the next few weeks, we will likely begin to start seeing dollar spot and I will be excited to see how these early season applications of plant growth regulators and fungicides function in producing good turf quality and resistance to disease.

Tim Sibicky
TSibicky@hotmail.com
Chicago District Golf Association
11855 Archer Avenue
Lemont, IL 60439

Conditions have been very wet in the Midwest this spring, which has resulted in a very fast growth rate of turf.  Most of us are having a hard time keeping up with mowing.  These wet conditions in spring are often followed by a leaf spot breakout in turf.  The picture below is from the Chicago area.  It shows the typical leaf spot symptoms on fairway bent.

Symptoms generally include blighting from the tip down on bent, rather than the standard leaf spot lesions seen on other species.  The turf on the area may also look like it is dry, even if the soil is wet.  The grass also takes on a brown "haze" when you look at it from a distance.

The fungi that causes this is usually attributed to Bipolaris or Dreschslera (formerly Helminthosporium), depending on the author.  I will let the pathologist sort that one out.

Chlorthalonil (Daconil and other commercial names) is the standard answer for this problem, although there are several fungicides labeled for this disease.

This disease can also hit greens, but most golf courses are treating greens and it is not as common as it once was.  Because of the cost, fewer superintendents are treating fairways and that is where we are seeing most of the problem this spring.
 

This is the first of the 2011 research reports. It includes the 2010 results from our trial on creeping bentgrasses maintained at both fairway and green height. Tables 3 and 4 are jpg photos and you will need to click on them to be able to read them.

Creeping Bentgrass Dollar Spot Study

Christopher J. Blume and Nick E. Christians

Objectives

The objectives of this study are to determine the susceptibility of creeping bentgrass (Agrostis stolonifera) cultivars to dollar spot (Sclerotinia homeocarpa) under both green height and fairway height.

Materials and Methods

This fairway height (0.5”) and green height (0.25”) studies are being conducted at the Iowa State University Turfgrass Research Station it is part of a regional project being conducted at several of the Midwestern Universities. Both studies included 24 cultivars, although some of the cultivars differed on the two sites (Table 1). The green-height study area was established on a sand-capped area, and the fairway-height area was established on a native soil area (Nicollet clay-loam).

Both studies were established 17 September, 2008. The plots were allowed to mature until the spring of 2009. The plots were then split into untreated and fungicide treated halves. The study was conducted as a randomized split block design, with three replications.

Fungicide treatment timing was based on the cultivar ‘Declaration’, which is the most dollar spot tolerant cultivar in the study. Treatments were made to the green height plots when ‘Declaration’ was observed to have at least 5% of the plot area infested with dollar spot. The fairway height study area was treated when ‘Declaration’ was observed to have at least 10% of the plot area infested.

The fungicide mixture consisted of Emerald (0.18 oz product/1000ft²) and Daconil Ultrex (3.2 oz product/1000ft²), applied in 2 gallons water/1000ft². The applications were applied using a modified spray boom, with two TeeJet XR flat fan nozzles. In 2010, three applications were made 24 June, 19 August, and 4 October.

Results

‘Memorial’ and ‘Penncross’, and ‘LS-44’ had the best quality ratings in the green height study in 2010, whereas ‘Allister’ received the lowest rating. In the fairway height study, ‘Alpha’, ‘LS-44’, and ‘Memorial’ were the highest rated cultivars, and ‘Independence’, ‘Declaration’ and ‘SR 1150’ received the lowest quality ratings (Table 2).

‘Century’ and ‘Imperial’ showed the most damage from dollar spot in both September and October in the green height study (Table 3). ‘Memorial’, ‘Declaration’, and ‘Crystal Bluelinks’ had the least damage in untreated plots at the end of the season.

There was not as much dollar spot in 2010 as there was in 2009 on the fairway height bentgrass. At the first two ratings of the season, there was more dollar spot in the treated side than in the untreated side of the plot. These plots had not been treated since the fall before. The reason for this observation is unknown. In August, no dollar spot was observed on treated or on untreated sides of the plot. In September, ‘Southshore’ and ‘Century’ had the most dollar spot on the untreated side of the plots, whereas ‘Memorial’, ‘Independence’, and ‘Declaration’ had the least dollar spot. In October, ‘Crenshaw’ and ‘Century’ had the most dollar spot and ‘Memorial’, ‘Alister’, ‘Pennlinks II’ and ‘Memorial’ had the least (Table 4).

The following is a post from a student named Steve Johnson. He is an undergraduate who was working for Dr. Mark Gleason on a pathology research project this summer. He is doing this as part of the requirement for his Hort 391 special studies course. Hopefully, this will start a trend and we will have several other posts like it this fall.

Steve Johnson, Soph. Summer Intern Blog #1

Many turfgrasses are susceptible to fungal diseases and this leads to many maintenance issues for turf practitioners.  In response to the detrimental effects of turf diseases caused by a wide assortment of fungi, a precise reading of the amount of turf infected by a disease is needed to determine the proper course of action.

In evaluating alternatives for suppressing turf diseases, its important to have a method to separate the effective treatments and the from the less effective ones.  This often requires replicated field trials, often at multiple sites, comparing each alternative in the same turfgrass stand.  But how, exactly, does one measure disease severity.

Disease severity is usually measured by some sort of visual estimation method.  In other words, you look at the turf that was treated with each respective fungicide treatment and try to visually estimate a number a represents how severe the disease symptoms appear.  This is not always accurate and may not be consistent from one rating to the next or from person to person.

As an example of this, lets consider the turf disease dollar spot, caused by the fungus Sclerotinia homeocarpa. Dollar spot is a relentless disease that is recognized by it distinctive lesions that are often the size of the a silver dollar and the lesions can grow together in severe cases.  Dollar spot is the most expensive disease to control on golf courses across much of the Midwest and Eastern United States.

In comparing dollar spot fungicide treatments to each other, how can we measure disease severity?  One way is to estimate the percentage of the plot that has turned brown due to the disease.  But one person rating the percentage of dollar spot may come up with a different number than someone else.  Others have two people rate the same plot independently of each other.  So how can we be sure that the disease ratings are consistent and reliable? 

Evaluating a way to accurately estimate dollar spot severity on greens-height creeping bentgrass was the objective of this study.  We wanted to find out how different two people would rate the same turf plots, and then average the ratings to reduce bias from individual ratings.  A trial was conducted during the summer of 2010 at the ISU Horticulture Research Station to evaluate dollar spot severity on creeping bentgrass.

The results of this study are mean to be relevant for disease severity ratings of many diseases and grasses, not just bentgrass and dollar spot.  
 

Figures

Examples of turf from the Hort farm plots infected with dollar spot.

1 and 2.

ISU Horticulture Farm turf plot marked out for the experiment. The white string was used to show where the corners of each were.  We then spray-painted the corners in order to visually locate where each plot was without the strings.  The strings were removed after all the corners had been painted so regular maintenance could continue.

WOI green located just north of Roy J. Carver Co-Lab on the northwest edge of the ISU campus.  It was marked out and prepared for the experiment in the exact same manner as the plots at the Research Station.