The Impact of Post Application Irrigation on Dollar Spot, Brown Patch and Algae Control with Renown Fungicide, 2008

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Julius Hicks
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1 The Impact of Post Application Irrigation on Dollar Spot, Brown Patch and Algae Control with 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, 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 fungicide utilizing five different (none, immediately, 4, 8 and 24 hours) irrigation timings following application. was applied at the same rate ( fl oz/1000 ft 2 ) 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 and three times per week. The study area received 1.5 lb N per 1000 ft 2 from (IBDU) in December of No fungicides have been applied since December of 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

2 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 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 ( ). 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 ( dollar spot infection centers per 25 ft2; DSIC). On that rating date, complete dollar spot control was observed in 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 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 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 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 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, treated plots had significantly better quality, when compared to the untreated control. treated plots subjected to the immediate irrigation treatment, had poorer quality when compared to all other 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 treated plots had less algae than the untreated control. No differences were observed among the 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 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

3 the later part of this study, dollar spot activity was beyond the acceptable level in the treated plots, however, 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 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.

5 Table 1. Visible fungicide on leaf and dollar spot control as influenced by post application irrigation with fungicide, 2008 Treatment Rate fl oz/1000ft 2 Post Application Irrigation Visible Fungicide on Leaf (0-5) a Dollar spot infection centers plot -1 b %Dollar spot b 26 May 1 June 1 Jun 8 Jun 22 Jun 29 Jun 4 Jul 11 Jul 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 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 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 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 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 a 46.3 a LSD (P=.05) Treatment Prob(F) * Treatments were applied on 25 May, 8 and 22 June 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.

6 Table 2. Percent of plot area blighted by Rhizoctonia solani as influenced by post application irrigation regimes, Treatment* Rate fl oz/1000ft 2 % Plot Area Blighted by Rhizoctonia solani a Post Application Irrigation 8 May 22 Jun 29 Jun 4 Jul 11 Jul None 0.0 b c 0.0 a 0.0 a 0.0 b 0.0 b Immediately Following 1.3 b 0.0 a 0.0 a 3.0 b 0.0 b 4 hours 0.0 b 0.0 a 0.0 a 0.0 b 0.0 b 8 hours 0.0 b 0.0 a 0.0 a 0.0 b 0.0 b 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) Treatment Prob(F) * Treatments were applied on 25 May, 8 and 22 June 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.

7 Table 3. Overall turfgrass quality and percent algae coverage as influenced by irrigation regime following applications of fungicide, Treatment Rate fl oz/1000ft 2 Overall turfgrass Quality (0-10) a % Algae b Post Application Irrigation 8 Jun 22 June 4 July 11 July 4 July None 8.85 a c 9.05 a 9.18 a 7.25 a 0.0 b Immediately Following 8.00 b 6.95 c 7.88 b 5.65 c 0.0 b 4 hours 8.53 a 8.10 b 8.68 ab 6.50 b 0.0 b 8 hours 8.65 a 8.83 ab 8.78 ab 6.40 b 0.5 b 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) Treatment Prob(F) * Treatments were applied on 25 May, 8 and 22 June 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

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