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!

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.

Soils Are Cooling – That’s Good and Bad

Recently, surface soil temperatures have been dropping below 70° F at night. While this is a good temperature range for growth of cool season grasses, it is a signal that much cooler soils are not far away. Grow of new seedings, overseedings, and turfs needing recovery will slow dramatically once soil temperatures break below the 60° F threshold. We have reached the time (October 1) where we no longer recommend seeding of most grasses except perennial ryegrass. Perennial ryegrass can be seeded as late as October 15 and still have high probability of develop a stand of turf.

If you need more growth out of your turf, this means there is little the time for action. Waiting another two weeks could be too late for any substantial growth through the rest of this year. In New Brunswick, the rain total for September has been very modest (1.23 inches) and there may be a need to irrigate to get recovery or better establishment of seedings before it is too cool.

Fertilization is another factor to evaluate. A turf that is healthy and vigorous probably doesn’t need fertilization but a thinning stand of grass with a sickly yellow-green color is likely to need some nitrogen fertilization. You need to soil test to figure out whether other nutrients such as phosphate and potash are needed.

Now is a good time to fertilize if the turf conditions warrant it. An application of 0.5 to 0.9 lb. of nitrogen per 1,000 sq. ft. is probably all that is needed for many turfs at this time of year. If the turf continues to struggle nutritionally (sickly yellow-green color), another application of 0.5 to 0.9 lb. of nitrogen per 1,000 sq. ft toward the end of October would be useful. At high rates (above 0.7 lb. of N), use a fertilizer product that contains slowly available nitrogen. Note that state law requires lawn fertilizers sold at retail (to homeowners) to contain slow release nitrogen. Also recall that state law prohibits nitrogen and phosphate fertilization by homeowners after November 15. Professional are prohibited from N and P fertilization after December 1.

Cool weather is about to limit the establishment of new seedings. In this photo, poor seed to soil contact will also inhibit the establishment of new turf.

Cool weather is about to limit the establishment of new seedings. In this photo, poor seed to soil contact will also inhibit the establishment of new turf.

 

The Rutgers Golf Classic is Almost Here!

The Rutgers Golf Classic will be held on May 5, 2014 at the Fiddlers Elbow CC in Bedminster Township, NJ.  This is a major regional turf research fundraiser that has attracted golfers from eight states and has raised over $1.3 million for the Rutgers Turf Research Program over the past 18 years.  To be a part of this great opportunity to support turf research and extension programs at Rutgers, access on-line registration information at www.njturfgrass.org or call the New Jersey Turfgrass Foundation at (973)-812-6467.

Turf Green-up Underway

It has been a long winter and delayed spring this year but yesterday’s rain and that of two weekends ago has “primed the pump” and initiated new growth of many turfgrasses and other plants. Thus, there is no more time to put off yard clean-up. Any leaves, branches and other debris dropped and blown around during the winter should be removed from turfs and other lowing growing landscape plantings. Otherwise early spring growth of plants will be impeded by any debris smothering those plants.

20140330_094107 (640x360)There has been little to no leaf growth of turf to this point, so mowing isn’t needed other than for help in picking up or mulching tree leaves.

For turfs forming a complete and dense ground cover, there is no urgency to fertilize. Let the grass wake up in response to warmer weather and rain. If it is important to get the grass growing, apply low to moderate (0.25 to 0.5 lb. per 100o sq. ft.) rates of nitrogen fertilizer. Fast acting fertilizer will obviously encourage more rapid green-up. Some examples of fast acting N included ammonium sulfate, blood meal (natural organic), fish meal (natural organic), and urea. Do not apply more than 0.5 lb. per 100o sq. ft of a fast acting fertilizer at this time. Over-applying nitrogen in the spring could result in extremely fast growing grass once the weather warms into the 60 to 70 degree F range. It is also increases the risk for nitrogen leaching in locations where that is a concern.

20140405_124606 (300x169)For turfs that have poor ground cover, be aware that soil erosion will be a serious risk at this time of year. Soils are wet and easily eroded during intense spring rains. Remember that soil erosion and water runoff from bare ground can carry nitrogen and phosphate into our waterways, contributing to the eutrophication process. Take action to stabilize the soil in these areas. If turf is the intended vegetative cover, apply a seed blend or mixture containing perennial ryegrass to these areas to re-establish cover and stabilize the soil. Perennial ryegrass will germinate under cool soil temperature and is useful in re-establishing cover. If you want to delay seeding until the weather is warmer, cover these areas with a wood mulch to reduce the soil erosion and runoff that will occur during each rain.

Drought Ends in New Jersey

Last autumn I was blogging about the drought conditions that we were experiencing. Thankfully, this winter’s precipitation, albeit lots of snow, has changed our water status in the region. The U.S. Drought Monitor no longer lists New Jersey as having abnormally dry or moderate drought. You can view more details at http://www.nrcc.cornell.edu/page_drought.html

Expect I will have to post about snow mold disease and flooding, once we get a thaw.

The current drought monitor map of the Northeast.

The current drought monitor map of the Northeast.

Cleaning-up Severe Crabgrass Infestations

If you’ve experience the number of rains that we have in New Brunswick, you are probably seeing plenty of crabgrass. Weather conditions have been ideal for crabgrass in many areas of the state.

You may be asking what can be done to clean-up this weed problem [Read more…]