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More on: Turf Weeds Research
Summary
1. Totally killed overseeded perennial ryegrass of all ages and at all rates:
Sencor® 75 (postemergence herbicide,
not labeled for cool-season grasses)
 2.
Moderately injurious to overseeded perennial ryegrass:
Surflan® A. S. (not labeled) and Pendulum®
WDG (labeled with warnings), both preemergence
3.
Little or no injury on older (46- and 67-day) overseeded perennial ryegrass:
Barricade® 65WG and Dimension®
(labeled with sufficient warning on age of grass), both preemergence
4.
No injury on older (46- and 67-day) overseeded perennial ryegrass
Drive® 75DF (labeled with warning on
age of grass), postemergence.
5.
Little or no injury on perennial ryegrass of all ages:
Prograss® EC (labeled with warning),
postemergence herbicide
This is a preliminary report of research data
in progress on the phytotoxicity of pre- and postermergence herbicides
to overseeded perennial ryegrass. This information may not be used
for management decisions, including the use of particular products.
The information is made available to stimulate discussion and careful
observation among turfgrass managers, chemical company representatives,
and others interested, regarding possible future directions for weed control
research.
Methods
A thin 'Tifgreen' (328) bermuda was overseeded on various dates in strips
with Lesco Double Eagle Blend perennial ryegrass, at 8.5 pounds per thousand
square feet. Research was conducted at University of Florida Fort
Lauderdale Research and Education Center. Dates of overseeding were
27 Dec. 1999, 17 Jan. 2000, 1 Feb. 2000, and 12 Feb 2000 which were 67,
46, 31, and 20 days, respectively before herbicide treatments on 3 Mar.
2000. On the day of herbicide treatment a dense stand of perennial
ryegrass covered all areas, except the 20-day-old ryegrass was thin.
Treatments were made with a 4-nozzle-boom, hand-held CO2 -pressurized
(40 psi, at the central distribution tube upstream from the boom) backpack
sprayer using nonoverlapping matched precipitation even flat fan nozzle
tips, two TeeJet 9502EVS (even flat spray tips) for the center two nozzles,
and two TeeJet UB8501SS (underleaf banding spray tips) for the outside
two nozzles. Nozzles were 30.5 cm (12 inches) apart on the boom and with
TeeJet 4193A strainer (100-mesh screen) and check valves, delivering an
average of 36.2 ml per second for the boom. Walking speed was 3
miles per hour, and the total effective spray swath was 37.25 inches,
thus spray volume was 30.5 gallons per acre.
| Table 1. |
Perennial ryegrass injury caused by
pre- and
postemergence
herbicides applied
at varying
rates
and varying days after overseeding.
Injury levels (% relative to untreated control,
UTC) averaged
across two
dates of application,
17 Mar. 2000
and 3 April 2000,
or
14 and 30
days
after chemical treatment.
|
|
| |
|
Rate of application |
| Herbicide |
Days after
planting |
0.5 x |
1 x |
2x |
| Barricade |
20 |
65 |
85 |
80 |
| Barricade |
31 |
43 |
55 |
65 |
| Barricade |
46 |
0 |
15 |
30 |
| Barricade |
67 |
0 |
0 |
5 |
| Dimension |
20 |
70 |
75 |
90 |
| Dimension |
31 |
35 |
45 |
70 |
| Dimension |
46 |
0 |
10 |
15 |
| Dimension |
67 |
0 |
0 |
0 |
| Drive |
20 |
75 |
70 |
75 |
| Drive |
31 |
45 |
40 |
35 |
| Drive |
46 |
0 |
0 |
0 |
| Drive |
67 |
0 |
0 |
5 |
| Pendulum |
20 |
85 |
90 |
90 |
| Pendulum |
31 |
68 |
75 |
75 |
| Pendulum |
46 |
20 |
50 |
65 |
| Pendulum |
67 |
18 |
50 |
48 |
| Prograss |
20 |
3 |
5 |
10 |
| Prograss |
31 |
5 |
5 |
5 |
| Prograss |
46 |
5 |
5 |
10 |
| Prograss |
67 |
0 |
0 |
0 |
| Sencor |
20 |
100 |
100 |
100 |
| Sencor |
31 |
100 |
100 |
100 |
| Sencor |
46 |
100 |
100 |
100 |
| Sencor |
67 |
100 |
100 |
100 |
| Surflan |
20 |
60 |
90 |
95 |
| Surflan |
31 |
65 |
75 |
80 |
| Surflan |
46 |
8 |
50 |
60 |
| Surflan |
67 |
5 |
35 |
45 |
| UTC |
20 |
0 |
0 |
0 |
| UTC |
31 |
0 |
0 |
0 |
| UTC |
46 |
0 |
0 |
0 |
| UTC |
67 |
0 |
0 |
0 |
|
Herbicides were mixed accordingly to provide the following rates of application:
Dimension® 1.5 fluid ounces per 1000 square feet; Barricade® 65WG,
1.125 pounds per acre; Pendulum® WDG, 2.5 pounds per acre; Prograss®
EC, 3 fluid ounces per 1000 square feet; Sencor® 75 0.333 pounds per
acre; Surflan® A. S. T/O 1 ounce per 1000 square feet; and a water-only
"untreated control" (UTC). The rates were typical rates
that were labeled for use in turf, but several of the products are not
labeled for use on perennial ryegrass. The Sencor rate was 0.5 the
maximum label rate. For purposes of discussion here, however, the
preceding rates are considered the "1 x" rate.
Applications were made at 7:30 am on 3 Mar. 2000, on a sunny day with
little breeze. There was no rain for 24 hours after treatment.
Plots were evaluated for percent ryegrass cover on 17 Mar. and 3 April
2000. Herbicide injury was calculated as the average reduction from
100%, averaged across the two dates of evaluation (Table 1).
Results
The range of injury varied from 0% for the untreated control (UTC)
to 100% for Sencor® (metribuzin). Triazine herbicides such
as Sencor® are known to be highly injurious to cool-season grasses,
so this was not surprising. While there was no replication in this
experiment, it was analyzed by analysis of variance with the three-way
interactions (chemical x rate x days) serving a pooled error.
Besides the varying effects of different chemicals, age of grass was
extremely important in predicting injury, even more so than the rate of
application. Averaged across the products, the more days since overseeding,
the less was the injury, with the biggest jump between 31 and 46 days,
and very little difference between 46 and 67 days.
Prograss® (ethofumesate) was the least injurious product, showing
10% injury when applied at the 2 x rate on 20-day-old grass. Drive®
75DF (quinclorac) showed unacceptable injury at all rates of application
to grass that was 20- and 31-days-old, but showed 0% injury to 46-day
and older grass.
The preemergence herbicides were surprising. Barricade® 65WG
(prodiamine), which was quite injurious in another experiment to perennial
ryegrass planted after chemical treatment, was safe on the oldest 67-day-old
ryegrass,even at the 2 x rate. This was approximately the same level
of phytotoxicity as Dimension® (dithiopyr). In contrast, Surflan®
A.S. (oryzalin) and Pendulum® WDG (pendimethalin) were moderately
to highly injurious to ryegrass at all rates of application and all days
since overseeding, with the exception of Surflan® at the 0.5 x applied
to the older (46- and 67-day-old) ryegrass.
How good are the labels?
The labels on the herbicides were sufficiently cautious to have prevented
injury. The label for Prograss® EC Herbicide (ethofumesate)
says the product may be applied "to overseeded bermudagrass in late
fall, one to two weeks after emergence of overseeded perennial ryegrass
to control annual bluegrass." The label on Drive® 75 DF
says that perennial ryegrass is highly tolerant, and Drive® 75DF can
be applied to it, but "do not apply within 4 weeks after seedling
emergence of perennial ryegrass."
The label for Barricade says, "do not apply to overseeded turf within
60 days after seeding or until after the second mowing, whichever is longer."
The label on Dimension® is similar, "the grass must have a good
root system and a uniform stand, and have received at least two mowings
following its seeding . . . ."
The Pendulum WDG label says, "applications made to overseeded warm-season
turfgrasses may cause thinning or injury of the overseeded species."
The label for Surflan AS says, "in bermudagrass areas that have
been overseeded with winter grasses, a spring application of Surflan AS
will thin the overseeded grasses, and elsewhere it says, "do not
apply Surflan AS to cool season turfgrass species." The label
for Sencor 75 Turf makes it clear that the product is only for bermudagrass
turf.
These results were obtained at a time of year when perennial ryegrass
dies naturally, so they probably portray a worse-case scenario for injury
than would normally be encountered in the field.
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