The Impact of Post Application Irrigation on Dollar Spot, Brown Patch
and Algae Control with Renown Fungicide, 2008
The middle plot was irrigated immediately following application.
This was the morning following the first application. Notice less of
a white ‘paint-like’ effect on that plot as compared to the top plot (no
water) and the bottom plot (irrigated 4 hours).
Introduction: Over the past few years there have been many pre-mixed fungicide products released for use in
the golf courses turf market. The benefits of these products include: synergistic mixes, resistance management,
ease of measuring and reduction of waste and trash. Sometime, there is a mix of two or three active ingredients
with two different modes of action. For example, Renown is a mix of azoxystrobin and chlorothalonil.
Chlorothalonil is a contact fungicide and previous research has shown that it controls foliar disease best when
applied to dry turf and allowed to dry. Azoxystrobin is an acropetal penetrant fungicide that moves upward
from the point of entry in the plant.
Hence, one of the most common questions with the uses of these products that contain more than one
active ingredient is 1.) how can I target a foliar disease and a stem of root disease with the same application and
2.) when is it safe to irrigate following application. Therefore, the purpose of this trial was to evaluate the level
of brown patch and dollar spot control with Renown fungicide utilizing five different (none, immediately, 4, 8
and 24 hours) irrigation timings following application. Renown was applied at the same rate (4.5 fl oz/1000 ft2)
on three occasions during the peak of dollar spot activity.
Material and Methods:
This trial was conducted on the ‘research tee’ at Philadelphia County Club, located in Gladwyne, PA.
Treatments were applied on 25 May, 8 and 22 June and using an 8004 flat fan nozzle to deliver 1.0 gallon per
1000 ft2 (44 gal/A) carrier volume. All application days where rain-free and all plots were treated with dew
present at approximately 6 AM. Water was applied immediately following, 4, 8 and 24 hours following
application to respective plots. Irrigation water was pre-measured and delivered using a garden watering can at
0.1 inch of water per 1,000 ft².
The study was maintained as a typical golf course tee (i.e., insecticides, herbicides and irrigation was
supplied regularly as needed). This site should be considered poorly draining and thatchy with a history of
severe algal (blue-green algae, cynobacteria), brown patch (Rhizoctonia solani) and dollar spot activity. The
turf consisted of ‘Princeville’ creeping bentgrass that was mowed at the height of 0.450 and three times per
week. The study area received 1.5 lb N per 1000 ft2 from 31-0-0 (IBDU) in December of 2007. No fungicides
have been applied since December of 2007.
Visible fungicide on leaf surface was rated on a 0 to 5 scale where 0=no visible white fungicide residue
on surface and 5.0= total upper leaf surface white with residue. Dollar spot infection centers per plot were
counted until 4 July when the infection centers had extremely coalesced. From that point forward dollar spot
was rated on a percent (%) blighted scale from 0 to 100 where 100= total plot area blighted. Percent plot area
blighted by Rhizoctonia solani and algae was rated on a percent (%) blighted scale from 0 to 100 where 100=
total plot area blighted. Overall turfgrass quality was rated on a 0 to 10 scale where 7.5 was the minimal
acceptable level of a bentgrass tee and 10=optimal quality, density and color. Percent plot area covered by algae
was rated on a percent (%) blighted scale from 0 to 100 where 100= total plot area blighted. All data,
application and rating dates are shown in tables below.
Results:
Many superintendents scout following applications of fungicides and many times the residue of
fungicides on the leaves indicated treatment. One day following the application of the Renown there were
significant differences in the white fungicide residue among treated plots. On 26 May, plots subjected to
immediate irrigation (0.73) had less white residue when compared to all other irrigation treatments (2.0-4.0).
All fungicide treated plots had more residue when compared to the untreated control. By 1 June (one week after
treatment one), plots subjected to the immediate irrigation treatment had equal white residue as the untreated
control which was significantly less than all other fungicide treatments. Plots subjected to the 4 hour irrigation
had fewer residue, when compared to the no irrigation and the 8 and 24 hour irrigation.
Dollar spot became active in the trial area and surrounds one week after the first treatment. On 1 June,
there was no significant differences in the level of dollar spot control, however, all fungicide treated plots had
minor levels of disease (0.0-2.3 dollar spot infection centers per 25 ft2; DSIC). On that rating date, complete
dollar spot control was observed in Renown treated plots subjected to 8 hour irrigation treatment. A similar
trend was observed on 8 June, when the untreated plots had an average of 33.5 DSIC and all fungicide treated
plots had less than 15. Although, not statistically different plots subjected to the immediate irrigation had the
greatest number of DSIC (15.0), which was more than none (3.8 DSIC), 4 hour (11.8 DSIC), 8 hour (10.8) and
24 hour (2.5 DSIC). Perhaps, the greatest differences on dollar spot control were observed on 22 June when
78.8 DSIC were observed in the untreated plots. Plots subjected to the immediate irrigation had 34.3 DSIC,
which was significantly greater than none (2.5 DSIC), 8 hours (5.3 DSIC) and 24 hours (4.0). All plots were retreated on 22 June and by 29 June complete dollar spot control had been observed in plots treated with Renown
and subjected to irrigation at the 24 hour timing. The level of dollar spot in all treated plots had decreased from
the 22 June rating, however, no statistical differences were observed. Agronomically, plots receiving Renown
and subjected to no, 4, 8 and 24 hour irrigation had the least dollar spot. Dollar spot pressure intensified during
the first week of July and 20% plot area blighted was observed in the untreated plots. On 4 and 11 July, the
highest level of dollar spot control was provided by Renown subjected to no irrigation.
Brown patch was also present in the trial area in early May, however, was not severe until early July.
On all rating dates, plots receiving Renown no matter the irrigation treatment provide high levels of brown patch
control.
The largest factor affecting turfgrass quality was dollar spot and brown patch. Hence, where the highest
level of disease control was achieved, the highest quality was observed. On all rating dates, Renown treated
plots had significantly better quality, when compared to the untreated control. Renown treated plots subjected
to the immediate irrigation treatment, had poorer quality when compared to all other Renown treatments on
every rating date.
Due to a prolonged period of high humidity during early July, algae had become present in the trial area.
All Renown treated plots had less algae than the untreated control. No differences were observed among the
Renown treatments.
Discussion:
The trial was conducted under high dollar spot and brown patch pressure. The data from this trial
provided valuable incite for superintendents when using Renown and targeting brown patch and dollar spot.
The highest level of consistant dollar spot control was observed in plots that received no irrigation following
treatment and 24 hour irrigation following treatment. There was no differences in the level of brown patch
control on any rating date among the treatments. All of the treated plots had less brown patch than the untreated
plots.
Dollar spot is considered a foliar disease and brown patch is considered a stem/lower shoot disease. In
the later part of this study, dollar spot activity was beyond the acceptable level in the treated plots, however,
Renown was still providing a high level of brown patch control. This may be due to the chlorothalonil being
removed from mowing and other environmental weathering and the azoxystrobin moving into plant tissue
rapidly and persisting for up to 19 days following application (11 July). It is likely that the prolonged brown
patch control provided by Renown was due to the azoxystrobin which had moved into the plant tissue in all
irrigation regimes. Future research with premix fungicide should target soil and crown diseases with the same
irrigation regimes to better understand the impacts of post application irrigation and targeting diseases like
summer patch, and anthracnose on putting green turf. Also, it would be interesting to examine other pre-mixes
like Concert (chlorothalonil + propiconazole) for their level of brown patch and dollar spot control under the
same five irrigation regimes.
Table 1. Visible fungicide on leaf and dollar spot control as influenced by post application irrigation with Renown fungicide, 2008
Visible Fungicide on
Rate
Post Application Irrigation
Dollar spot infection centers plot-1 b
%Dollar spot b
Treatment
Leaf (0-5) a
fl oz/1000ft2
26 May
1 June
1 Jun
8 Jun
22 Jun
29 Jun
4 Jul
11 Jul
Renown
4.5
None
4.00 a c
3.0 a
0.3 a
3.8 b
2.5 c
1.5 b
0.90 b
6.0 b
Renown
4.5
Immediately Following
0.73 c
0.0 c
2.3 a
15.0 b
34.3 b
14.3 b
4.75 b
23.5 b
Renown
4.5
4 hours
2.00 b
2.0 b
0.3 a
11.8 b
11.3 bc
1.5 b
1.08 b
15.5 b
Renown
4.5
8 hours
4.00 a
3.0 a
0.0 a
10.8 b
5.3 c
1.3 b
1.25 b
15.5 b
Renown
4.5
24 hours
4.00 a
3.0 a
0.3 a
2.5 b
4.0 c
0.0 b
1.08 b
10.5 b
Untreated
None
0.00 d
0.0 c
7.3 a
33.5 a
78.8 a
82.5 a
20.00 a 46.3 a
LSD (P=.05)
0.092
0.00
5.05
17.66
28.15
28.72
10.638
17.77
Treatment
0.0001
1.0000
0.0518
0.0233
0.0002
0.0001
0.0096
0.0033
Prob(F)
* Treatments were applied on 25 May, 8 and 22 June 2008.
a
Visible fungicide on leaf surface was rated on a 0 to 5 scale where 0=no visible white fungicide residue on surface and 5.0= total upper leaf surface
white with residue.
b
Dollar spot infection centers per plot were counted until 4 July when the infection centers had extremely coalesced. From that point forward dollar
spot was rated on a percent (%) blighted scale from 0 to 100 where 100= total plot area blighted.
c
Means in the same column followed by the same letter are not significantly different according to P=0.05.
Table 2. Percent of plot area blighted by Rhizoctonia solani as influenced by Renown post application irrigation regimes, 2008.
Rate
Treatment*
% Plot Area Blighted by Rhizoctonia solani a
fl oz/1000ft2
Post Application Irrigation
8 May
22 Jun
29 Jun
4 Jul
11 Jul
Renown
4.5
None
0.0 b c
0.0 a
0.0 a
0.0 b
0.0 b
Renown
4.5
Immediately Following
1.3 b
0.0 a
0.0 a
3.0 b
0.0 b
Renown
4.5
4 hours
0.0 b
0.0 a
0.0 a
0.0 b
0.0 b
Renown
4.5
8 hours
0.0 b
0.0 a
0.0 a
0.0 b
0.0 b
Renown
4.5
24 hours
0.0 b
0.0 a
0.0 a
0.0 b
0.0 b
Untreated
None
17.0 a
12.5 a
11.3 a
20.0 a
26.3 a
LSD (P=.05)
10.50
11.37
10.16
6.64
9.18
Treatment Prob(F)
0.0188
0.1675
0.1625
0.0001
0.0001
* Treatments were applied on 25 May, 8 and 22 June 2008.
a
Percent plot area blighted by Rhizoctonia solani was rated on a percent (%) blighted scale from 0 to 100 where 100= total plot area blighted.
c
Means in the same column followed by the same letter are not significantly different according to P=0.05.
Table 3. Overall turfgrass quality and percent algae coverage as influenced by irrigation regime following applications of Renown fungicide, 2008.
Overall turfgrass Quality (0-10) a
% Algae b
Treatment
Rate fl oz/1000ft2
Post Application Irrigation 8 Jun 22 June
4 July
11 July
4 July
c
Renown
4.5
None
8.85 a 9.05 a
9.18 a
7.25 a
0.0 b
Renown
4.5
Immediately Following
8.00 b 6.95 c
7.88 b
5.65 c
0.0 b
Renown
4.5
4 hours
8.53 a 8.10 b
8.68 ab
6.50 b
0.0 b
Renown
4.5
8 hours
8.65 a 8.83 ab 8.78 ab
6.40 b
0.5 b
Renown
4.5
24 hours
8.68 a 8.90 a
8.95 a
6.40 b
0.8 b
Untreated
None
7.15 c 5.88 d
5.25 c
4.00 d
12.5 a
LSD (P=.05)
0.368
.786
0.990
0.685
6.23
Treatment Prob(F)
0.0001 0.0001
0.0001
0.0001
0.0034
* Treatments were applied on 25 May, 8 and 22 June 2008.
a
Overall turfgrass quality was rated on a 0 to 10 scale where 7.5 was the minimal acceptable level of a bentgrass tee and 10=optimal quality, density
and color.
b
Percent plot area covered by algae was rated on a percent (%) blighted scale from 0 to 100 where 100= total plot area blighted.
c
Means in the same column followed by the same letter are not significantly different according to P=0.05.
Water Immediately
Untreated
4 Hour Irrigation
8 Hour Irrigation