Crabgrass and Goosegrass Control in Fine Turf

Over the past 7 to 10 days, warm-season weeds have really turned the corner and are growing rapidly. It’s probably no coincidence that 5-day average soil temperatures finally pushed past 70 degrees about 10 days ago in central NJ. Until last week, most of the crabgrass I observed was growing slowly with a chlorotic appearance. Now it has taken on the more characteristic lime green hue and is growing more rapidly than surrounding cool-season turf. Where previously it was mostly present in thin area of turf, it’s now beginning to make an appearance in dense stands of fine turf such as fairways and greens.

Smooth crabgrass with its characteristic hue in a poor stand of perennial ryegrass on June 23, 2017.

With this post, I’m going to focus mostly on control in in creeping bentgrass where herbicide options are limited. Now is a good time to scout historically problematic areas for small crabgrass and goosegrass plants. If left uncontrolled and allowed to tiller, crabgrass control in creeping bentgrass fairway turf is difficult and with risk of bentgrass injury.

Leaf stage smooth crabgrass in an annual bluegrass/creeping bentgrass fairway.

Fenoxaprop (Acclaim Extra) can be applied at 3.5 fl oz/A for control in bentgrass fairways. This rate is 8 to 10X lower than what can be applied to ryegrass, bluegrass and tall fescue to control larger crabgrass plants. At the 3.5 fl oz/A rate, multiple applications on 2 to 3 week intervals may be required to provide control of small leaf-stage crabgrass. If crabgrass is allowed to tiller, even multiple applications of fenoxaprop at rates labeled for use in bentgrass fairways may be a losing battle, so scouting is important. Quinclorac (Drive XLR8, Quinclorac 75DF) is an option to control tillered plants in bentgrass. At rates labeled for use in creeping bentgrass multiple applications may be required. Refer to the label for more information about rates, turfgrass tolerance and adjuvants.

Fenoxaprop will also provide suppression or control of small goosegrass plants. However, once goosegrass begins to tiller, fenoxaprop is less effective at low rates.

Topramezone (Pylex) is an effective herbicide for goosegrass control in cool-season turf. However, in creeping bentgrass fairways, Pylex is labeled for application at up to 0.25 fl oz/A. Tolerance may vary depending on bentgrass cultivar and other management practices. Topramezone causes bleaching of susceptible plant tissue and while limited bleaching is not detrimental to fairway turf from an agronomic perspective, it is very noticeable to even a casual observer. I hate to copy instructions from a bottle of carpet cleaner, but it’s a good idea to make an application to a small area of bentgrass and wait 10 to 14 days to make sure the bleaching you observe is acceptable. My experience with low rates of topramezone for goosegrass control is limited, but multiple applications may be required depending on plant size. Include methylated seed oil or crop oil with Pylex per the product label. Other cool-season grasses such as Kentucky bluegrass, ryegrass, tall fescue and fine fescue are more tolerant than creeping bentgrass and application at higher rates is permitted.

Crabgrass and goosegrass will continue to germinate throughout the summer. If you are observing significant breakthrough in areas already treated with a pre-emergence herbicide consider applying a pre-emergence herbicide with a different mode of action than previously applied. One example is Anderson’s Goosegrass/Crabgrass Control, which contains oxadiazon. Oxadiazon is a PPO inhibiting herbicide, not a mitotic inhibiting herbicide like most other pre-emergents (i.e., bensulide, dithiopyr, pendimethalin, prodiamine). Anderson’s Goosegrass/Crabgrass Control should be applied to dry turf and is labeled for use on bentgrass putting greens. Another example of an herbicide with a different mode of action is Tower (dimethenamid-P). Tower is labeled for use on bentgrass fairways and tees. Read the label for more information on turfgrass tolerance to both of these products.

For information on crabgrass and goosegrass ID and control other turfgrass areas, see this previous post.

The mention of trade names and rates is for educational purposes and does not imply endorsement by the author, Rutgers Center for Turfgrass Science, or the New Jersey Agricultural Experiment Station. Always defer to the product label for instructions on properly applying an herbicide.

Weeds off to a Slow Start

Despite a quick start to the spring, soil temperatures remain low across the much of the state. Average soil temperatures (3-inch depth) have been hanging around the mid 60s in central NJ and many warm-season weeds such as crabgrass have hardly developed despite germinating over 6 weeks ago. This crabgrass at our research facility has not advanced past the leaf stage and I have observed this across the region over the past few weeks.

Smooth crabgrass in the leaf stage

The peak of annual bluegrass seedhead production has passed. It was a very difficult spring to properly time ethephon applications for optimum seedhead suppression. If the results of our seedhead suppression research trial are indicative of the region, then I suspect those that made a fall (December at the snow mold fungicide timing) application of ethephon were happy with suppression. Spring-only applications did not perform very well in our research.

A very seedy annual bluegrass putting green at Hort. Farm No. 2

When warmer weather arrives, warm-season weeds will develop rapidly. If you are relying exclusively on post-emergence herbicides for crabgrass control, an application of a post-emergence herbicide in the next few weeks may be warranted. This will only control what has already germinated and not what will emerge as we continue into the summer, so additional applications will be necessary. Especially if using fenoxaprop (Acclaim Extra, Last Call), lower herbicide rates often can be used when treating smaller plants. Mesotrione (Tenacity) is another post-emergence crabgrass herbicide that is most effective on smaller plants. Quinclorac (Drive XLR8, Quinclorac 75DF) is another post-emergence option but is often more effective against larger (> 4 tiller) plants than the smaller plants present right now. Topramezone (Pylex) has efficacy some against crabgrass but is an extremely effective product for goosegrass control. See the herbicide labels for more information.

We observed goosegrass emergence two weeks ago at certain sites but not others. This event is not particularly relevant for those who applied a pre-emergent herbicide. However, you may want to scout areas with a history of goosegrass problems to make sure your pre-emergence herbicide is working. Goosegrass seedlings can be difficult to differentiate from crabgrass seedlings. Goosegrass seedlings have a ridged adaxial leaf surface (ridges look similar to perennial ryegrass) and a blunt leaf tip while crabgrass seedlings are relatively smooth with a sharper leaf tip. If you applied a pre-emergence herbicide and are already seeing goosegrass germination please contact me.

Goosegrass seedlings

If you plan to make an herbicide application to control broadleaf weeds, the weather continues to be ideal for control and growth of the cool-season grass into voids. This is especially true for the summer annual knotweed.

Prostrate knotweed observed mid-May in New Brunswick

 

Prostrate knotweed is more easily controlled now while it is still relatively immature. Standard three-way or other broadleaf herbicides that contain 2,4-D may not provide complete control. So in the case of severe infestation, products that contain triclopyr (e.g., T-Zone, Battleship III, 4-Speed XT, Cool Power, others) will provide more control. Cultural practices such as aerification to reduce compaction and improve conditions for turf growth are also essential. For more information on whether you will disrupt the pre-emergence herbicide barrier by aerifying, see this information from Dr. Aaron Patton.

To Aerify or Not to Aerify when Using a Preemergence Herbicide

 

Sedges and Kyllingas

This week I visited several golf courses and other sites along the Garden State Parkway from Exit 9 (Cape May) to Exit 171 (A few miles from the NY State line. In terms of plant development, northern NJ seems to be about a week behind central NJ and southern NJ seems to be a week or two ahead of central NJ. The most noticeable difference across locations is the difference in kyllinga emergence from dormancy. In southern NJ, kyllinga is close to full emergence while kyllinga northern NJ is at approximately 50% emergence. In all locations, but especially those in southern NJ, now would be a good time to begin making applications if you haven’t already.

False-green kyllinga dominating a stand of tall fescue

False green kyllinga (foreground) has a lime green color compared to the tall fescue (background).

 

Our research indicates that halosulfuron-methyl and imazosulfuron are effective options for control. Multiple applications will likely be necessary for effective control. Make follow-up applications after you observe re-growth from the previous application (usually 3 to 4 weeks later). For more information see this previous blog post by Dr. Murphy. https://turfblog.rutgers.edu/?p=934#more-934.

Soil Temperatures

Soil temperatures have been steadily warming since late March at Hort Farm No. 2 (North Brunswick). Temperatures consistently ran above 50 degree Fahrenheit in early April, and between 50 and 60 degrees from 10 to 27 April.

May 1st was the fifth consecutive day of the maximum soil temperature reaching at least 65 degrees. Thus, soil temperatures are essentially entering into an ‘ideal’ period for the growth of cool-season turfgrasses.

Those experienced with managing summer patch may recall that 5 consecutive days with a soil temperature maximum of 65 degrees is the threshold for initiating a preventive summer patch control program. Isn’t it ironic that ideal growth of the fungus that causes summer patch is synchronized with ideal growth temperatures for cool-season turfgrasses.

Damage from summer patch disease, however, typically is not seen until later in the summer when heat and drought stresses make it challenging for plants with a compromised root system to survive.

summer patch disease on hard fescue

Severe summer patch disease on hard fesuce at Hort Farm No. 2 in July 2013.

Some Early Disease Activity

Sorry no pictures for this post, but thought I would share some recent observations. The recent rains and warm night on Friday/Saturday brought out two diseases on annual bluegrass earlier than we typically experience at the research farm in North Brunswick NJ (Hort Farm No. 2).

Saturday morning, our graduate student found nickel- to quarter-sized spots of foliar Pythium on his annual bluegrass plots. Tended to be more spots on his plots with greater N fertility but the disease was also on low N plots. This is the earliest I have experienced foliar Pythium, but the Friday/Saturday nighttime temperature didn’t get much below 65 degrees F, ‘good’ for Pythium.

Also on annual bluegrass, was a slight outbreak of dollar spot on Saturday morning. Dollar spot in April is early but not unheard of in NJ.

You might notice that the pests mentioned have shown up first on annual bluegrass.

Hurry Up and Wait. Now Go!

At the beginning of March we were potentially a week or two away from annual bluegrass seedhead emergence thanks to an extremely warm February. Cooler temperatures prevailed and significant snowfall across much of the Northeast brought soil temperatures down and put the brakes on annual bluegrass development for a few weeks. It’s now the beginning of April and we are very close to annual bluegrass seedhead emergence on putting greens in central New Jersey. Parts of northern New Jersey appear to be about a week behind the New Brunswick area.  If you haven’t already applied ethephon (i.e., Proxy, Ethephon 2 SL, Oskie) for seedhead suppression, this week might be ideal (see previous post for more information) for most courses in New Jersey.

Warmer temperatures this week will likely bring average 24-hour soil temperatures (one inch depth) into the 50s and turf will begin to grow more rapidly. Emergence of summer annual weeds is not far away. I first noticed prostrate knotweed emergence in mid February. These early germinating plants survived the winter weather and will continue to develop this week.

Prostrate knotweed seedlings

Note that knotweed seedlings will have two seed leaves and crabgrass will have only one.

Prostrate knotweed seedling with two seed leaves

 

Smooth crabgrass seedling with one seed leaf

I have not observed crabgrass emergence, even on south-facing slopes. I spent the latter part of last week in Washington D.C. and could not find any crabgrass along sidewalks and bare areas there either.

Crabgrass emerging with one seed leaf (in a previous year)

Depending on your location, forsythia may or may not be a reliable phenological indicator for crabgrass germination this year. In a normal year, pre-emergent herbicides (except for dithiopyr (Dimension), which can control crabgrass up to the pre-tiller stage) should be applied when forsythia is in full bloom because crabgrass germination will occur shortly thereafter. However, extremely cold temperatures killed or injured many forsythia flowers in central Jersey and areas south.

In northern New Jersey I’ve observed forsythia plants still in the bud stage and in this case they are likely to be effective indicators. Especially this year, it is important to use multiple forsythia plants because the bloom timing is affected by location among other factors. Plants that bloomed early were injured by the winter weather, but others were unaffected as this photo from @samcamuso demonstrates.

Soil temperature at a 1-inch depth has been reported as a reliable indicator of crabgrass germination assuming soil moisture is adequate. In a three-year study, Fidanza et al. (1996) found that crabgrass began to emerge when the soil temperature at a 1-inch depth averaged 57 to 63 degrees during a 7-day period. Soil temperatures at our research center in North Brunswick have been well below this threshold as of this writing. At this time we are holding off on making pre-emergent applications to our research trials. However, in southern New Jersey soil temperatures are warmer and crabgrass will germinate sooner. In these areas, making a pre-emergence herbicide application soon would be timely. If you are worried you may be too late, scout bare areas with crabgrass carcasses, especially those on south-facing slopes, as crabgrass will germinate earlier in these areas.

Making pre-emergent herbicides applications early is not thought to reduce efficacy. However, if you are using dithiopyr (i.e., Dimension) it’s a good idea to wait until shortly after emergence and take advantage of the early post-emergence efficacy this product provides against crabgrass.

Of course don’t forget to consider your potential renovation/seeding projects this spring. If you are planning on seeding, do not apply any pre-emergence herbicide.

Literature Cited

Fidanza MA, Dernoeden PH, Zhang M (1996) Degree-days for predicting smooth crabgrass emergence in cool-season turfgrass. Crop Sci. 36:990-996.

Warm Air, Cool Soil

Warm air temperatures build anticipation of plant growth but keep in mind that cool soil temperatures will strongly moderate growth during the spring. Turf growth typically will be very slow until [Read more…]

Winter Damage

 

snow plow damage

Sod pieces removed by snow plowing.

While the warm weather has allowed many of us to get out and enjoy the outdoors, you may have noticed [Read more…]

Annual Bluegrass Seedhead Suppression

In weed management on golf courses, annual bluegrass (Poa annua) seedhead (inflorescence) suppression often kicks off the growing season. Plant growth regulators can be used to suppress seedhead production if applications are properly timed. Much like pre-emergence herbicides that are not effective if applied after weed emergence, PGRs are less effective if applied too late.

It is common to make two or three sequential applications of trinexapac-ethyl (i.e., Primo Maxx, T-Nex) + ethephon (i.e., Proxy, Ethephon 2 SL) or ethephon alone in the spring. Timing the first application can be difficult. One method is to make the first application at the first sign of the “boot” stage. Annual bluegrass is considered in boot stage when the stem is swollen, indicating that it contains a seedhead (pictured below).

A swollen annual bluegrass stem indicating this plant is in the “boot” stage.

If the leaf tissue is carefully removed from the stem layer by layer, it will reveal the inflorescense (pictured below), which you can usually see with your naked eye or the aid of a hand lens.

A relatively immature inflorescence of annual bluegrass visible after plant dissection and the aid of a dissecting microscope.

A more mature seedhead visible to the naked eye after stem dissection.

This seedhead will continue to move up the stem, eventually emerging. Once the seedhead emerges from the stem the plant is considered post boot stage. Using the boot stage method to time applications requires careful inspection of several plants at various times during the spring. To predict booth stage on a putting green, it is best to check south facing slopes and higher cut turf, as seedhead emergence in these areas will be ahead of putting greens.

Growing degree-day models have been developed as alternatives to boot stage-based PGR application timings. One model developed by Dr. Ron Calhoun at Michigan State University (gddtracker.net) uses a base temperature of 32 degrees F and a target of 200 to 500 GDD with accumulation beginning February 15th. However, to my knowledge this model has not been validated in the Northeast region. The unusually warm winter may make this model less reliable. On the day this was written, our research farm in North Brunswick has accumulated 40 GDD32 since February 15th. If the weather occurs as predicted, we may reach 200 GDD32 by Sunday February 26th when more seasonal weather returns.

Another GDD model common to the Northeast region uses a base temperature of 50 degrees F and a target accumulation of 50 GDDs beginning February 1st. However, I am not aware of any published literature validating this model in this region. On the day this was written, our research farm in North Brunswick has accumulated 8 GDD50 since February 15th. If the weather occurs as predicted, we may reach 30 GDD50 by Sunday when more seasonal weather returns.

A combination of GDD tracking and scouting for boot stage may be useful to time PGR applications. Scout roughs and bare areas with annual bluegrass for boot stage and seedhead emergence. As we approach the GDD threshold, scout roughs, fairways, and greens more intensely for boot stage and seedhead emergence. Boot stage is typically observed in late March or early April in New Jersey so we are still likely several weeks away. However, if temperatures remain warm it may arrive earlier this year.

Recent research from Dr. Shawn Askew at Virginia Tech has demonstrated efficacy of ethephon applications made just before winter dormancy followed by spring applications of trinexapac-ethyl + ethephon. We have a trial underway at Rutgers to evaluate the efficacy of fall applications in this region in collaboration with Dr. Zane Raudenbush at Ohio State. In addition to validation of this fall application strategy in multiple regions, research to ensure fall or winter applications of ethephon do not increase the potential for annual bluegrass winterkill may be necessary. For more information on Dr. Askew’s research visit http://www.golfdom.com/a-new-key-to-poa-annua-seedhead-suppression/

Fun Fact: Annual bluegrass seed can become viable even if the seedhead is removed from the plant on the same day it is pollinated. Just another reason this weed is so competitive in turfgrass!

Note: Embark (mefluidide) also provides excellent annual bluegrass seedhead suppression when used properly, but it is no longer being manufactured.

We will continue to scout for annual bluegrass seedhead emergence. To share your own observations and for updates from Rutgers, follow @RUturfweeds on Twitter!

Weather Ideal for Pythium and Brown Patch

The weather this summer has been very conducive for brown patch and Pythium blight diseases. I have received number requests this summer to address turf problems related to one or both of these diseases in lawns, sports fields, sod and now my own plots.

Suspected initial outbreak of Pythium on velvet bentgrass maintained at a 0.110-inch height that occurred over the weekend (August 7) in a cultivation trial at Hort Farm No. 2 in North Brunswick NJ.

Suspected initial outbreak of Pythium on velvet bentgrass maintained at a 0.110-inch height that occurred over the weekend (August 7) in a cultivation trial at Hort Farm No. 2 in North Brunswick NJ.

The weather forecast for the rest of this week indicates [Read more…]

Licensing for Mosquito Control – Category 8B

I have been getting questions from landscape/turf professionals about licensing for mosquito control. I asked Dr. George Hamilton about where to direct professionals with these questions.

Information on licensing of professionals for mosquito control can be found on the Rutgers Cooperative Extension Pest Management website: http://pestmanagement.rutgers.edu/PAT/

You can get a core manual and category 8B manual at your county extension office.