Crabgrass is Now Germinating at Most Indiana Locations

The GDD Tracker website (sponsored by the MRTF and Purdue University) is predicting that crabgrass is now germinating at most Indiana Locations (see figure below). The GDD Tracker estimated that crabgrass germinated in Lafayette, IN after Wednesday this week and I was able to confirm this by identifying newly germinated crabgrass (see figure below) both in Lafayette and West Lafayette.

For those of you that have not yet applied a preemergence herbicide (crabgrass preventer), it is still possible to control crabgrass if you choose a product that contains dithiopyr – the only preemergence crabgrass herbicide that also has some early postemergence activity on crabgrass.

The weather is now changing. We will continue to monitor the growing conditions and provide updates as needed on turf growth and turf pests in 2012.

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New Turf Publication: Facts About Phosphorus and Lawns

A new turf publication has been posted on the Turf website:

Facts About Phosphorus and Lawns - AY-334
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When Will Crabgrass Germinate?

With the rapidly warming weather, several are asking “When will crabgrass germinate?” The reason this is so important is because preemergence herbicides used for the control of crabgrass must be applied prior to emergence (except dithiopyr (Dimension) which can be used postemergence on crabgrass up to 1-tiller). There are several different ways to try and anticipate when crabgrass might germinate. My favorite is the GDD Tracker website. This blog post is an expansion of a post in 2011 with more information and sources.

Soil Temperature: Research says that crabgrass begins to germinate when the average daily soil temperatures reach 57 to 64 °F at a one-inch depth although large quantities of crabgrass seedlings will not start germinating until soil temperatures increase to 73 °F or above at a one-inch depth (Fidanza et al., 1996). Soil growing degree days (in contrast to the air temperature model highlighted below) have also been sued by others to predict large crabgrass emergence (Myers et al., 2004). The problem with using soil temperatures to predict germination is that most turf managers do not have access to daily soil temperature averages or are not collecting data with their own stations for their location. Going outside and collecting a soil temperature measurement with a thermometer provides only an instantaneous measurement and not an average over time.

Air Temperature Using Growing Degree Days: Because it is often inconvenient to obtain soil temperature data and often easier to track air temperature; consider using a growing degree day (GDD) model based upon air temperatures. Research suggests that 200 GDD need to accumulate with a base of 50 °F ( before crabgrass germinates (source: Dr. Ron Calhoun). Currently (March 16, 2012), the models show that crabgrass still has not germinated in southern Indiana but that it is about to emerge. This still allows for the application of a preemergence herbicide if not yet treated.

Plant Phenological Indicators: The flowering of landscape plants can also be used as a good estimate of when crabgrass might be germinating. Many are aware that forsythia is traditionally considered a good plant to indicate that crabgrass will soon start germinating. Forsythia will be in full bloom prior to crabgrass germination and forsythia flowers will wither near crabgrass germination (Masin et al., 2005; Cardina et al., 2011). Most think that crabgrass germinates when forsythia blooms, but this is false. Instead, turf managers should use forsythia blooms as an encouragement to hurry up and get their preemergence application made before crabgrass begins to germinate. Other plants common in the landscape that bloom before crabgrass germinates include saucer and star magnolia and Bradford Callery pear (Cardina et al., 2011). The initiation of redbud blooms and sometimes crabapples are also a good indication of when crabgrass may germinate (Cardina et al., 2011). However, having said all this, researchers have also documented that ornamental plant flowering is not always a consistent predictor of crabgrass germination, especially with forsythia (Fry et al., 2001).

  1. Cardina, J., C.P. Herms, and D.A. Herms. 2011. Phenological indicators for emergence of large and smooth crabgrass (Digitaria sanguinalis and D. ischaemum). Weed Technol. 25:141-150.
  2. Fidanza, M.A., P.H. Dernoeden, and M. Zhang. 1996. Degree-days for predicting smooth crabgrass emergence in cool-season turfgrass. Crop Sci. 36:990-996.
  3. Fry, J., S. Rodie, R. Gaussoin, S. Wiest, W. Upham, and A.Zuk. 2001. Using flowering ornamentals to guide application of preemergence herbicides in the Midwestern U.S. International Turfgrass Soc. Res. J. 9:1009-1012.
  4. Masin, R., M.C. Zuin, and G. Zanin. 2005. Phenological observations on shrubs to predict weed emergence. Int. J. Biometeorl. 50:23-32.
  5. Myers, M.W., W.S. Curran, M.J. VanGessel, D.D. Calvin, D.A. Mortensen, B.A. Majek, H.D. Karsten, and G.W. Roth. Predicting weed emergence for either annual species in the northeastern United States. Weed Sci. 52:913-919.

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Unwinter, Poa seedheads and Growing Degree Days, Oh MY!!!

As the “un-winter of 2011-2012” rapidly winds to a close golf course managers are already bringing their playing surfaces into peak form. For those managing putting surfaces containing annual bluegrass (Poa annua) this means addressing concerns that seedheads are affecting surface smoothness. With the lack of snow cover this past winter, the seedhead season is already off to a rapid start and seedheads in putting green turf are developing quickly! There are several cultural practices that can help minimize seedheads but treatment with a chemical plant growth regulator (PGR) provides the most consistent suppressive results.

Product choices: PGRs have been used for many years and currently there are not many new chemistries on the market. Historically, the most reliable choices have been; mefluidide (Embark or Embark T/O = less formulation) and ethephon (Proxy, several other brand names) or an ethephon + trinexapac-ethyl (TE:Primo Maxx, T-Nex and many other brand names) tank-mix. Mefluidide is normally a one time application thus, proper application timing is essential to success (unfortunately all plants do not produce seedheads at the same time/rate). Many consider it the “gold standard” for seedhead suppression. Any dissatisfaction with this product has been related to the missing the ideal application window and the risk for turf yellowing, particularly for Kentucky bluegrass surrounds. Many managers have moved away from using mefluidide on putting surfaces but it is still frequently used for higher cut fairway turf.

A popular alternative with very good suppressive properties is the ethephon + TE tank mix. The purported main advantage to the ethephon + TE combination is that the addition of TE with ethephon will minimize the yellowing (a “Granny Smith” apple green color) compared to ethephon applied alone. Additionally, the ethephon + TE combo is involves multiple applications (a second application should occur approximately 21 days following the first) which brackets seedhead development. Thus, many managers report more consistent seedhead suppression with this tank-mix compared to the single mefluidide application.

The use of other plant growth regulators like paclobutrazol, flurprimidol or TE alone, only slightly suppresses or delays seedhead emergence. These PGRs will not, however, minimize the seedheads to the extent of a mefluidide or ethephon + TE tank-mix. The addition of TE with ethephon also enhances turf color, however, research has shown where ethephon applied alone or tank-mixed with TE significant scalping (Dernoeden and Pigati, 2009) can occur when a TE program is not continued. Another consideration with any of the seedhead products would be the inclusion of a chelated iron source. This will further enhance green color and mask any potential PGR discoloration.

Timing: There are a number of managers who still use the “feel”, experience or local knowledge method to determine application timing. Another suggestion has been to initiate a seedhead program based after the second “true” mowing or when the turf is actively growing. While prior experience should still be a part of the decision to initiate, there are also more quantitative methods to help make this decision. Several models are available based on accumulating growing degree days (GDD) or heat units. The GDD models are based on the high and low air temperatures and utilize a “base” temperature. The most common method for calculating GDD is:

GDD = (max temp + min temp)/2 - “base temperature” (normally either 32 or 50 F)

Example: If we had a day with a maximum temperature of 76 and a minimum of 50 and used a base temperature of 50 the calculation would be: GDD = (76 + 50)/2 - 50 = 13, or for this single day 13 GDD. Remember there are no negative GDDs, a negative number is considered a zero and GDDs are summed across time (e.g. GDD day 1 = 3, day 2 = 4, day 3 = 15 would be 22 GDDs). You can do this on your own with a spreadsheet program and the weather data, but in our region (IN, IL, MI, OH) the growing degree day tracker located at is an extremely useful tool that calculates for you.

Differences in base GDD temperatures? In prior years a base temperature of 50 was once used. Research conducted at Michigan State suggested that the GDD 50 base model often overestimated a few early warm days in the season and due to the higher base temperature and low number of GDD units required to reach the application threshold the model quickly passed the application target range. Thus, the GDD50 model is no longer used and a base temperature of 32 now used for the model.

What to do? This spring (2012) GDDs have accumulated quite rapidly. The target for initiating an ethephon + TE program is normally between 200 and 250 GDDs, some suggest a specific number 220 and applications will be out of range at 500 GDD. In other words managers that start once 500 GDD accumulate should expect less than satisfactory results.

For many, in the region it is already time to apply the initial ethephon + TE tank-mix. For example, in Indianapolis this past Sunday (11 March) saw GDD exceed the initial threshold of 200 at 228 GDD and today (15 March) GDDs are predicted to be 320. In Lafayette, the initial threshold was met on Monday (3-12) at 236 GDD and today we will see 300 GDD. Way up north in Bristol the initial threshold will be met today at 212 GDD.

The take home point is that it is time to start treating for seedheads and as I talk to people in Indiana this initial application is about 11 to 14 days sooner than when they applied last year. The models are tools along with experience and as you gather “quantitative information” for your 2012 agronomic plans don’t forget to check out our tools on the Purdue Turfgrass Web-site as well as other online tools like Syngenta’s Pest Outlook Maps

Dernoeden, P. H., and R. L. Pigati. 2009. Scalping and creeping bentgrass quality as influenced by ethephon and trinexapac-ethyl. [Online]Appl. Turfgrass Sci. p. 1-7.

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Activity of Turfgrass Pathogens

A new posting has been added to Turfcast.

See Turfcast ( to read more about this post and for a daily summary of risk for several turfgrass diseases.

Rick Latin, Turfgrass Pathologist

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Get your motor running: Crabgrass control adjustment

With warm temperatures this winter many are questioning how to adjust their turf management practices in 2012. In the past 90 days, Indiana temperatures have averaged 3-4 degrees warmer than normal. The forecast also shows that we will likely continue to be warmer than normal during the next 30 days.

Although I do not foresee the need to make significant changes to your management program, it will be necessary to start making preemergence applications earlier this year in my opinion. Here are some things to consider as you adjust.

How will the warmer conditions affect my preemergence timing? Some believe that despite the warmer weather, that it is not necessary to make preemergence applications early in 2012 because we will very likely get a “killing” frost in April which could kill all the crabgrass that germinates early. While I think this is possible, my experience is that many warm-season grass seedlings (whether crabgrass or bermudagrass) are largely unaffected by spring frosts. The reason for this is not completely clear, but it is likely that these seedlings are insulated from frosts that occur at the top of the turf canopy because the emerged seedlings, such as crabgrass, are protected next to the warmer soil surface. Since I do not believe that there is a guarantee that a late spring frost will kill emerged crabgrass, then I recommend making sure that you apply your preemergence herbicide early this year prior to emergence. Just how early is uncertain, but it would not hurt to target making applications 7-10 days earlier than normal. To track crabgrass germination and the optimum window for preemergence applications, check the following website

How can I get extended crabgrass control? Split or sequential applications are a strategy for improving crabgrass control with preemergence herbicides. The general strategy is to split the application from one application into two applications using the same total amount of product. The first application would be applied before crabgrass germinates at a one-half rate at the normal application timing and the second application would be made approximately 60 days later at a one-half rate. For example, Dimension 2EW would be applied at 1 pint/acre (0.25 lb a.i./acre) on April 1 and a second application would be made with Dimension 2EW at 1 pint/acre (0.25 lb a.i./acre) on June 1. This would equal a total of 2 pints/acre or 0.5 lb a.i./acre. Research at Purdue shows that crabgrass control can be increased by about 20% using a split application strategy compared to a single preemergence application.

Aaron Patton
Turfgrass Extension Specialist

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Purdue Turf Bowl Teams Place in the Top Ten in Las Vegas!!!

Purdue students continue to protect their “turf” among the rise of new competitors at the 18th Annual Collegiate Turf Bowl Competition hosted during the 2012 Golf Course Superintendents Association of America (GCSAA) International Golf Course Conference and Show in Las Vegas, NV.

The three and one-half hour competition this year challenged student’s knowledge of more practical concepts of turfgrass management including disease, insect, seed, equipment, weed, irrigation and turfgrass identification. The competition covers mathematics, plant physiology, plant growth and development, human resource and financial management. Purdue’s performance in the competition over the last ten years has helped to bring additional recognition to the university, college and department. The students placed 6th, 9th, 25th, and 50th out of 87 teams from across the nation. Agronomy student’s Tony Feitz, John Thackery, Joey Gerking, Zak Peterson, CJ Coy, Jon Conatser, Quin Stilwell, Chris Sandels, Jason Hazel, Lucas Braun, Peter Westfall, TJ Mueller, Chad Melton and Dane Alexander represented Purdue at the competition. Despite weekly practices, with two hour-long study sessions starting in September students fell shy of their goal of finishing first but were extremely excited about their strong finish. Purdue once again solidifies its reputation as one of the top schools in the nation.

Students are already looking forward to next year’s competition at the GCSAA Show in San Diego, CA and the STMA competition in Daytona Beach, Fl. They have set their sights on placing first and are committed to achieving that goal. The teams would like to acknowledge the financial support they received this year from the Agronomy Department and the Midwest Regional Turf Foundation. The teams would also like to thank Ryan Baldwin, CGCS, Greg Shaffer, Jon Trappe, Quincy Law, Tracy Tudor, and their advisor Dr. Cale Bigelow for contributing their time to help educate and prepare the students. Please congratulate the 20112 Turf Bowl Teams on their performance and hard work the next time you see them.
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2012 = Same Pests But Earlier ETA

With the very mild winter that most of Indiana experienced so far, we are being asked about its effect on insect populations for this year. The consensus among turfgrass entomologists is that although insect populations were probably not especially hurt by low temperatures this winter, they probably have not benefitted that much either. Insect pests have developed behavioral and physiological strategies to get through even very cold winters, so the lack of cold this winter probably will not affect the kinds of pests we have this year. However, because the emergence of insects is tied directly with temperature accumulations, we do expect to see insects emerge much earlier during years with mild winter compared to more normal years. In fact, we are already seeing the late winter emergence of many arthropods such as lady beetles, clover mites, and crane flies that usually begin later in March. Take for example clover mites. We are already receiving calls about these very tiny mites (smaller than a pin head) that may occur in high numbers, first around windows, but later over entire walls of buildings.

Clover mites most often originate in turfgrass stands that are relatively young (2 – 5 yrs old), well maintained and fertilized. During the late winter and again in the fall time, these mites seem to migrate in large numbers and often end up inside structures, including homes. Clover mites are small enough to squeeze through the tiniest of cracks and openings in buildings, making it nearly impossible to seal them out. Turfgass grown right up to and in direct contact with building foundations can also facilitate their entry into structures. Although they are harmless to humans and pets, the presence of large numbers of these mites inside structures can be unsettling and attempts to wipe or sweep them from light colored surfaces such as walls often smashes them, resulting in brown/red steaks that can be difficult to clean.

The temporary application of double-sided tape around window sills can help stop migrating mites from gaining further access into affected structures, but once inside, these mites often become dehydrated rather quickly making vacuum cleaning of their tiny dead bodies one of the best options.

Clover mites are very tiny as can be seen on this ruler. To most people they appear as tiny, moving, black specks. Under magnification, however, they are reddish in color and have characteristically long front legs. This character helps separate them from the hundreds of other different mites.

Clover mites can be prevented from entering a home or building by using perimeter treatments. These may be either physical or chemical. A physical barrier can be established by separating turfgrass (where the mites feed) from the perimeter wall of the building. A strip of clean cultivated soil or stone, free of grasses, that extends 18 – 24 inches out from the foundation is usually sufficient to deter these mites from crossing. Ornamental plants that are not clovers or grasses may be added to increase the attractiveness.

Chemical barrier treatments may be applied to the outside foundation perimeter (three feet high and three feet out). Soaps as well as pyrethroid insecticides have been shown to be effective IF applied during the times that the mites are on the move.

Use of chemicals inside the home is not recommended. Remember that these mites do not directly damage the building nor do they bite people. Most consider them a simply a temporary nuisance pest and find that vacuuming or wiping them up with a soft sponge or wet cloth is sufficient. Be aware that they can smear and leave a red stain if crushed.

Timothy J. Gibb, Extension Entomologist

Douglas Richmond, Turfgrass Entomologist

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