Experiments on bermudagrass encroachment
into creeping bentgrass greens were conducted at the Georgia Station from
1986 through 1991. The experiments were conducted in four phases:
First experiment - 1986
- A preliminary study was conducted to identify herbicide-plant growth
regulator (PGR) treatments that showed maximum injury to bermudagrass and
minimum creeping bentgrass injury. Several herbicides applied alone or
with PGRs were applied to pure stands of each grass mid-May. Herbicide-PGR
treatments and rates of application are given in Table 1. From these treatments,
Tupersan, Cutless, Tupersan + Cutless, Prograss + Cutless, and Prograss
+ Embark were selected to include in the second experiment.
Table 1. Herbicide-PGRs and rates of
application. Experiment I, 1986.
| TREATMENTS1 | RATE LB AI/A |
|---|---|
| Untreated | - |
| Tupersan | 48.0 |
| Prograss | 1.5 |
| Embark | 0.5 |
| Limit | 3.0 |
| Cutless | 1.0 |
| Prograss + Cutless | 1.0 + 0.38 |
| Prograss + Embark | 1.0 + 0.12 |
| Prograss + Limit | 1.0 + 0.75 |
| Tupersan + Cutless | 48 + 0.38 |
| Tupersan + Embark | 48 + 0.12 |
| Tupersan + Limit | 48 + 0.75 |
Second experiment - 1987 and
1988 - The herbicide-PGR treatments selected from the first experiment
were applied to creeping bentgrass inter planted with Tifway, Tifgreen,
and common bermudagrasses at rates given in Table 2. Each chemical was
applied late September plus mid-April or only as a single mid-April application.
All herbicide-PGR treatments injured creeping bentgrass higher when applied
in September than when applied in April. The higher injury in September
occurred because bentgrass root system had not recovered from the summer
stress. There was no advantage in bermudagrass suppression during May and
June from September plus April treatments when compared with the single
April treatment.
Table 2. Herbicide-PGRs and rates of
application. Experiment II, 1987-1988.
| TREATMENTS | RATES
LB AI/A |
DATE APPLIED1 |
|---|---|---|
| Untreated | - | - |
| Tupersan | 48.0
48.0 |
September + April
April |
| Tupersan + Cutlass | 48.0 + 0.75
48.0 + 0.75 |
September + April
April |
| Tupersan + Embark | 48.0 + 0.38
48.0 + 0.38 |
September + April
April |
| Cutlass | 1.25
1.25 |
September + April
April |
| Prograss + Cutless | 1.5 + 0.75
1.5 + 0.75 |
September + April
April |
| Prograss + Embark | 1.5 + 0.38
1.5 + 0.38 |
September + April
April |
When Embark was mixed with Tupersan
or Prograss and applied in April, creeping bentgrass injury was severe
(>30%). The injury to bentgrass from other chemicals applied in April was
within an acceptable (<30%) range.
Bermudagrass was effectively suppressed
from April herbicide-PGR treatments from late May to early June, but the
grass recovered rapidly after these dates. In all instances, Tupersan +
Cutless and Prograss + Cutless suppressed bermudagrass growth more than
Tupersan and Cutless applied alone.
These results indicate that Tupersan
+ Cutless and Prograss + Cutless were safe to apply to creeping bentgrass
in April. Bermudagrass was effectively suppressed from both combination
treatments for approximately 6 weeks following a single April application.
Third experiment - 1988 and 1989
- Cutless applied alone or in sequence with Tupersan or Prograss was applied
in multiple applications during spring and summer to creeping bentgrass
inter planted with Tifway, Tifgreen, and common bermudagrasses. All chemicals
were applied initially mid-April. The rates and frequency of applications
are given in Table 3.
Table 3. Herbicide-PGR rates and frequency
of application. Experiment III, 1988-89.
| CHEMICAL |
|
||
|---|---|---|---|
| APRIL 15 | JUNE 1 | JULY 12 | |
| Untreated | - | - | - |
| Cutless | 1.25
1.25 1.25 1.25 |
-
1.25 0.63 0.63 |
-
- - 0.63 |
| Tupersan + Cutless | 48 + 0.75
48 + 0.75 48 + 0.75 48 + 0.75 |
-
48 + 0.75 24 + 0.38 24 + 0.38 |
-
- - 24 + 0.38 |
| Prograss + Cutlass | 1.5 + 0.75
1.5 + 0.75 1.5 + 0.75 1.5 + 0.75 1.5 + 0.75 |
-
1.5 + 0.75 0.75 + 0.38 0.75 + 0.38 1.5 + 0.75 |
-
- - 0.75 + 0.38 1.5 + 0.75 |
Prograss + Tupersan and Prograss +
Cutless were safe to creeping bentgrass when each was applied April 15
at a full rate and followed by one-half rate on June 1. The injury was
increased to an unacceptable level when the June 1 application was increased
to a full rate or when one-half rates were applied June 1 and July 12.
The injury was severe when Cutless was applied as repeated treatments in
June or July regardless of rate.
Cutless did not generally suppress
bermudagrass growth effectively after June 1 regardless of rates and frequency
of applications. Tupersan + Cutless applied at full rate in April and followed
by one-half rate June 1 effectively suppressed bermudagrass growth until
mid-June to mid-July. The suppression with Tupersan + Cutless was not improved
when the rate the second application was increased or when a third application
was made July 12. Prograss + Cutless applied at full rate in April and
one-half rate June 1 suppressed bermudagrass growth effectively until mid-August
1988, but the suppression 1989 was effective only until early June. These
results show that repeated chemical applications suppressed bermudagrass
growth longer than did a single application. Although the suppression was
higher from Prograss + Cutless than from Cutless or Tupersan alone, none
of the chemicals provided consistent bermudagrass suppression at rates
included in this experiment throughout the summer both years.
Fourth experiment - 1989 through
1991 - Bermudagrass inter planted into creeping bentgrass was winter
killed in 1990. Bentgrass tolerance was evaluated for 3 years (1989 through
1991) and bermudagrass suppression was evaluated in 1989 and 1991 from
the herbicide-PGR treatments. Prograss + Cutless and Tupersan + Cutless
were applied initially to creeping bentgrass inter planted with bermudagrasses
at a full rate March 12 or April 8 ± 1 week. Repeated applications
at one-fourth rates were made at various times after the original application.
Time and frequency rates of herbicide-PGR applications are given in Table
4. Siduron was applied at a full rate to separate plots in March and April
and at monthly intervals through August. Acclaim was applied initially
in April and at monthly intervals through August.
Table 4. Herbicide-PGR rates and frequency
of application. Experiment IV, 1989-1991.
| CHEMICAL | RATE
LB AI/A |
APPLICATION DATE1 |
|---|---|---|
| Untreated | - | - |
| Prograss
+ Cutless |
1.5 + 0.75
+ 0.75 + 0.38 |
April 8
May 24 |
| 1.5 + 0.75
+ 0.38 + 0.19 |
April 8
May 24 + Jun 16 |
|
| 1.5 + 0.75
+ 0.38 + 0.19 |
April 8
May 24 + Jun 16 + Jul 9 |
|
| 1.5 + 0.75
+ 0.38 + 0.19 |
April 8
May 24 + Jun 16 + Jul 9 + Jul 26 |
|
| 1.5 + 0.75
+ 0.38 + 0.19 |
March 12
Apr 29 + May 20 + Jun 10 |
|
| 1.5 + 0.75
+ 0.38 + 0.19 |
March 12
Apr 29 + May 20 + Jun 10 + Jul 1 |
|
| Tupersan
+ Cutless |
48 + 0.75
+ 12 + 0.19 |
April 8
May 24 + Jun 16 + Jul 9 + Jul 26 |
| 48 + 0.75
+ 12 + 0.19 |
March 12
Apr 29 + May 20 + Jun 10 + Jul 1 |
|
| 48 + 0.75
+ 12 + 0.19 |
March 12
Apr 29 + May 20 + Jun 10 + Jul 1 + Jul 24 |
|
| Tupersan | 48 | Apr 8 + May 9 + Jun 9 + Jul 8 + Aug 9 |
| 48 | Mar 12 + Apr 8 + May 9 + Jun 9 + Jul 8 + Aug 9 | |
| Acclaim | 0.13
+ 0.07 |
Apr 8
May 9 + Jun 9 + Jul 8 + Aug 9 |
| 0.07 | Apr 8
May 9 + Jun 9 + Jul 8 + Aug 9 |
Prograss + Cutless applied initially
at a full rate in March or April injured creeping bentgrass more in 1989
and 1990 than in 1991. However, the injury was temporary and bentgrass
recovered fully within 3 to 4 weeks. Bentgrass tolerated the one-fourth
Prograss + Cutless treatments throughout the spring and summer. Tupersan
applied alone or with Cutless caused moderate to severe injury to bentgrass
during spring and summer 1989, but not the following 2 years. Bentgrass
injury to Acclaim was severe each year and should not be applied to bentgrass.
Tupersan applied in March and April
to separate plots and repeated at monthly intervals suppressed the growth
of Tifway and common bermudagrass until after mid-June, but the bermudagrass
recovered from the treatments by mid-July. Tifgreen was not suppressed
with Tupersan after June 1. Acclaim suppressed common bermudagrass throughout
the spring and summer, but the chemical had little effect on growth of
Tifway or Tifgreen bermudagrasses.
Tupersan + Cutless applied initially
in March suppressed bermudagrass more than when treatment was delayed until
April when each treatment date was followed by four timely one-fourth applications.
Tifway and common bermudagrass treated with Tupersan + Cutless in March
and followed by timely repeated applications were effectively suppressed
until after late July, but recovered in August. Tifgreen bermudagrass treated
at the same time was suppressed until after mid-June but recovered in July.
Prograss + Cutless suppressed bermudagrass
similarly whether the initial application was made in March or April, providing
four timely one-fourth rate applications were made. When compared with
untreated turf, the suppression of Tifway and Tifgreen bermudagrass was
approximately 74% and common bermudagrass was approximately 87% in early
September from Prograss + Cutless treatments. These results indicate that
multiple Prograss + Cutless treatments suppressed bermudagrass longer than
did Tupersan applied alone or with Cutless.
Summary. The growth of
either Tifway, Tifgreen, or common bermudagrass was effectively suppressed
throughout the spring and summer with Prograss + Cutless. The suppression
was similar whether chemicals were applied initially at full rate (1.5
+ 0.75 lb ai/A) mid-March or early April, providing four timely applications
at one-fourth rates were made during spring and summer. The second application
should be made at 6 weeks after the initial application and then repeated
at 3 weeks. To obtain optimum bermudagrass suppression with Prograss +
Cutless, it is important to apply the initial treatment from the time bermudagrass
starts to break dormancy until the turf is about 20% green. It is also
important to repeat the applications on schedule. When treatments are delayed
for only a few days, bermudagrass growth may occur and Prograss + Cutless
will not be effective after bermudagrass initiates growth.