Lawn Overseeding
Examination of Repetitive Overseeding And Four Herbicide Regimes To Improve Low-Input
Turfgrass Areas In Autumn
A Report To The New York State Turfgrass Association
Principle Investigator: David Chinery, Senior Resource Educator, Cornell
Cooperative Extension of Rensselaer County, 61 State Street, Troy, NY 12180,
(518) 272-4210, dhc3@cornell.edu
Cooperator: Dr. Frank Rossi, State Turfgrass Extension Specialist, 20 Plant
Science, Cornell University, Ithaca, NY 14853, fsr3@cornell.edu
Introduction: Turfgrass managers are constantly faced with the
need to improve the turfgrass density and quality in sports fields, golf courses,
and commercial and home lawns. Due to increased environmental concerns (real
and perceived) and stricter laws regarding the use of pesticides, the options
for maintaining and improving turf density and quality are diminishing. Concurrently,
the call for “organic” lawn care continues to increase. Many turfgrass
managers are searching for organic ways to suppress weeds, and currently extremely
few possibilities exist.
Dr. Frank Rossi has recently demonstrated that heavy overseeding
with perennial ryegrass (Lolium perenne) in fall can dramatically
increase turfgrass density on sports fields (Proceedings of the Cornell
Turfgrass Field Day, 2003). Research conducted by Cornell Cooperative
Extension of Rensselaer County on two Capital District sports fields, funded
by the New York State Turfgrass Association (NYSTA), has also shown this to
be a very effective method ( “Heavy Repetitive Fall Overseeding
To Improve Low-Input Sports Fields: A Report To The New York State
Turfgrass Association,” November 2003).
While repetitive overseeding has been demonstrated on sports
fields, it has not been explored for use in fall home lawn renovation. Traditional “partial
renovation” techniques for home lawns include the use of a selective
herbicide to reduce broadleaf weeds, followed by core cultivation, and a single
overseeding. These methods are time consuming, expensive, and sometimes beyond
the means of turfgrass professionals and homeowners managing low-input areas.
The results of one-time overseeding are often variable, according to anecdotal
information from turfgrass professionals. This project examined the effectiveness
of heavy, repetitive overseeding to improve turfgrass density when initiated
in autumn on a home lawn site using various combinations of seed application
timing, herbicide, and seed rate.
Objective:
To determine any increase in turfgrass density achieved by overseeding with
perennial ryegrass at four rate/timing schedules and with four herbicide regimes
in autumn on a home lawn site.
Procedures: The study site was a residential lawn in Castleton, NY, containing
a perennial ryegrass/Kentucky bluegrass/fine fescue turf with a large population
of broadleaf plantain and ground ivy. The plots received no fertilizer or irrigation
during the study. Each plots measured 9 square feet (3’ x 3’),
and each treatment had three replicates. Untreated check plots were also included.
Four herbicides were selected for this study. Each herbicide represented a
different approach to renovating a weedy home lawn.
- A selective herbicide (containing 2,4-D, mecoprop, and dicamba*) was chosen
to represent the traditional partial renovation scenario.
- The broad spectrum
herbicide glyphosate (RoundUp**) was used to kill all weeds and turfgrass
entirely, then the overseeding was done to re-establish the turfgrass.
- Two
rates of acetic acid herbicide were used to study the effectiveness of a “reduced-risk” herbicide.
In previous studies, acetic acid was noted to be an effective broad spectrum
herbicide initially, but Kentucky bluegrass re-grew in some conditions (Using Acetic Acid (Vinegar) As
A Broad-Spectrum Herbicide, fact sheet produced by Cornell Cooperative
Extension of Rensselaer County, 2002). Acetic acid was used in this study
at the 5% (low) and 20% (high) rates. While products containing acetic acid
at the 5% and 20% concentrations are available commercially, laboratory-grade
acetic acid was used in this study.
Four seed rates and timing schedules were used, as described in Table 1. The “6-Once” treatment
represented traditional partial renovation techniques, where seed would be
applied to the site one time. Three other treatments used repetitive overseeding,
with the timing and rates based on previous studies. ‘Pizzazz’ perennial
ryegrass was used in this study.*** A highly accurate Gandy drop spreader was
used to apply the perennial ryegrass seed according to the treatment schedule
listed in Table 1. All herbicides were applied on August 5, 2004. Overseeding
started on August 26, 2004. The treatments found in Table 1 were made to plots
treated with one of the four herbicides listed above, for a total of sixteen
different treatments.
Table 1: Seeding rate, timing, total number of applications and total pounds
of seed applied for four treatments
Treatment Name | Seeding rate (lbs./M) | Timing | Total number of applications | Total lbs. of seed/M |
6-Once | 6 | One application on August
26 | 1 | 6 |
6-Alternate | 6 | Alternate weeks | 3 | 18 |
2-Alternate | 2 | Alternate weeks | 3 | 6 |
2-Sequential | 2 | Sequential (3 weeks in a row) | 3 | 6 |
A four foot by four foot “weed square” was used to estimate turfgrass
and weed populations, and the proportional area bare of vegetation, at the
conclusion of the study.
Results: Untreated check plots had an average of 16.7% turfgrass, with the
remainder weeds, throughout the study. Other plots used in the study initially
had between 10 to 30% turfgrass, with the remainder weeds.
The low rate of acetic acid plots showed the smallest increase in turfgrass
during the study. Increase in turfgrass ranged from 57.0% for the 2-Sequential
plots to 64.3% for the 2-Alternate plots. Average final turfgrass ranged from
80.3% for the 2-Sequential plots to 87.3% for the 6-Once plots. Weeds in these
plots were not killed outright by the low concentration of acetic acid, and
were able to re-grow and competed successfully with the new turfgrass seedlings.
There was no bare ground visible in these plots, as all space was occupied
by either weeds or turfgrass. Data is presented in Table 2.
Table 2: Average initial turfgrass, average final turfgrass, and average increase
in turfgrass for plots treated with acetic acid herbicide at the low rate
Treatment Name | Average initial turfgrass (%) | Average final turfgrass (%) | Average increase in turfgrass (%) |
6-Once | 26.7 | 87.3 | 60.7 |
6-Alternate | 20.0 | 82.0 | 62.0 |
2-Alternate | 20.0 | 84.3 | 64.3 |
2-Sequential | 23.3 | 80.3 | 57.0 |
Data for the high rate of acetic acid treatments is presented in Table 3.
Average increase in turfgrass ranged from 65.7% for the 6-Once plots to 71.3%
for the 2-Alternate plots. Average final turfgrass ranged from 85.0% in the
2-Sequential plots to 91.3% in the 2-Alternate plots. The acetic acid used
at the high rate in these treatments reduced the weed population more effectively
than the low rate, allowing more seedling turfgrass to germinate and develop.
As with the low rate acetic acid treatments, there was no bare ground visible
in these plots, as all space was occupied by either turfgrass or weeds.
Table 3: Average initial turfgrass, average final turfgrass, and average increase
in turfgrass for plots treated with acetic acid high herbicide at the high
rate
Treatment Name | Average initial turfgrass (%) | Average final turfgrass (%) | Average increase in turfgrass (%) |
6-Once | 21.7 | 87.3 | 65.7 |
6-Alternate | 16.7 | 87.5 | 70.8 |
2-Alternate | 20.0 | 91.3 | 71.3 |
2-Sequential | 18.3 | 85.0 | 66.7 |
The data for the plots treated with glyphosate is presented in Table 4. While
the average initial turfgrass data is presented, all of the vegetation in these
plots (weeds and turfgrass) was killed with the herbicide. Essentially, all
of the turfgrass measured in the plots at the end of the study was comprised
of new seedlings. Because of this, measuring the average increase in turfgrass
for these treatments would have been meaningless. Average final turfgrass ranged
from 90.0% in the 2- Sequential plots to 96.0% for the 6-Alternate plots. There
were very few weeds in these plots, with some of the space not filled in with
new seedlings remaining bare.
Table 4: Average initial turfgrass, average final turfgrass, and average increase
in turfgrass for plots treated with glyphosate (Roundup) herbicide
Treatment Name | Average initial turfgrass (%) | Average final turfgrass (%) |
6-Once | 25.0 | 91.7 |
6-Alternate | 21.7 | 96.0 |
2-Alternate | 21.7 | 93.3 |
2-Sequential | 20.0 | 90.0 |
The 2,4-D treatments had the highest average increase in turfgrass and the
highest final turfgrass measurements in the study. Average increase in turfgrass
ranged from 73.0% for the 6-Once treatments to 84.7% for the 2-Alternate treatments.
All treatments had more than 98.0% turfgrass at the end of the study. Virtually
no weeds or bare ground was present in these plots at the end of the study.
Data for these plots is presented in Table 5.
Table 5: Average initial turfgrass, average final turfgrass, and average increase
in turfgrass for plots treated with 2,4-D herbicide
Treatment Name | Average initial turfgrass (%) | Average final turfgrass (%) | Average increase in turfgrass (%) |
6-Once | 26.7 | 99.7 | 73.0 |
6-Alternate | 25.0 | 100.0 | 75.0 |
2-Alternate | 15.0 | 99.7 | 84.7 |
2-Sequential | 20.0 | 98.3 | 78.3 |
Conclusions: The four herbicide treatments representing various lawn renovation
programs provided a variety of results. The low rate of acetic acid combined
with overseeding resulted in a significantly better quality lawn than the untreated
plots, with 57.0 to 64.3% more turfgrass. However, these plots still contained
13 to 20% weeds. The high rate of acetic acid performed better, increasing
turfgrass by 65 to 71%, and resulting in a lawn with 9 to 15% weeds. These
alternatives may prove attractive to a homeowner who does not want to use traditional
herbicides, but who would be willing to use a “reduced risk” herbicide
and would be interested in having a less weedy, but not weed-free, lawn.
The glyphosate treatments resulted in an entirely new stand of seedling turfgrass.
While final turfgrass density was high for all seeding regimes (90.0% or greater),
biodiversity was lost, since the former lawn of three turfgrass species was
replaced with a lawn entirely of perennial ryegrass.
The plots treated with 2,4-D provided the greatest average increase in turfgrass
density and greatest average final turfgrass density. This is not surprising,
since 2,4-D allowed the existing turfgrass to remain while managing the broadleaf
weeds very effectively. The overall appearance of these plots at the end of
the study would be acceptable to a homeowner desiring a very high quality lawn.
There were some small differences among the seeding rates and timing schedules.
For both of the acetic acid herbicides and the 2,4-D herbicide, 2-Alternate
seeding outperformed all other regimes. For the glyphosate treatments, 2-Alternate
seeding was second in performance only to 6-Alternate, which used three times
more seed. 6-Once represented what many consider the standard approach to overseeding
turfgrass. The 6-Once plots were the least successful with 2 of the 4 herbicide
treatments, and came in a close second to last in the remaining two treatments.
While the differences are small, and the data pool is limited, there is some
indication that stretching the application dates of seeding over several weeks
increases the eventual density of a turfgrass stand.
Additionally, timing of seed application seems more critical than total amount
of seed used. The 6-Alternate plots (with a total of 18 lbs./M applied) produced
turfgrass of the greatest density only in the glyphosate treatments. Under
these conditions, a total of 6 lbs./M of seed applied was adequate to provide
good results. Applying more seed would be wasteful and not cost effective.
Core cultivation, which is recommended as part of standard partial renovation
practice, was not used in this study, and good results were achieved. It appears
that repetitive overseeding without core cultivation is a method worthy of
more research.
* “Green Thumb Lawn Weed Killer” containing 7.59% 2,4-D dimethylamine
salt, 3.66% mecoprop dimethlyamine salt, and 0.84% dicamba dimethlyamine salt
** “Roundup Weed and Grass Killer” concentrate containing
50.2% glyphosate
*** ‘Pizzazz’ perennial ryegrass seed supplied courtesy of
Preferred Seed Company, Inc., 575 Kennedy Road, Buffalo, NY
Photos of treatments at the end of the study
