PERSONNEL: Hongfei Jiang, Jack Fry, and Ned Tisserat
SPONSORS: Heart of America Golf Course Superintendent's Association, Kansas Golf
Course Superintendent's Association, Kansas Golf Association
INTRODUCTION:
The 1994 Kansas turfgrass survey indicated that water was the greatest concern of golf course superintendents in the state. Golf course managers often face public scrutiny because of high summer water usage during peak demand periods in urban areas and fear of potential health and environmental problems posed by pesticide application. Water officials from Johnson County, Kansas and the Wichita Public Works Department report that golf courses account for 2 to 5% of water used during peak demand periods in summer. Consequently, golf courses have been provided a water budget based upon mean water usage and pay significant fines if total water use exceeds the budgeted allotment. The potential influence of irrigation management on environmental issues related to golf course turf is underestimated. Irrigation influences disease incidence and fungicide requirements; weed encroachment and herbicide requirements; and clipping production and mowing requirements. More data are needed on the influence of irrigation management on turfgrass pest problems.
MATERIALS AND METHODS:
This experiment was conducted at the Rocky Ford KSU Turfgrass Research Center. Two irrigation regimes, three herbicide treatments, and three fungicide treatments were arranged in a split-split plot design. Soil was a silt loam (fine, montmorillonitic, mesic Aquic Arquidolls).
Irrigation treatments (whole plots) were i) daily application of 0.3 inches water and ii) irrigation to replace 80 to 100% of atmometer-estimated evapotranspiration (ET) on 3 days weekly. Irrigation whole plots measured 6 X 12 m. Mean weekly irrigation amounts were determined using collection cups to determine irrigation output. Time required to deliver the desired amount of water then was calculated. Irrigation treatments began on 11 July and ended on 11 September.
Herbicide treatments (subplots) were i) preventive spring application of dithiopyr at 0.5 lb. a.i./a on 15 April and ii) curative postemergence herbicide application of fenoxaprop-ethyl (Acclaiim) at 0.38 lbs a.i./a plus 2,4-D + MCPP + Dicamba (Trimec Classic) on 20 July. Herbicide subplots measured 2 X 12 m.
Fungicide treatments (sub-subplots) were i) preventive applications of flutolanil (Prostar)
at 2 oz product/1,000 sq ft for brown patch suppression on 9 June, 12 July, 3 August, and 27
August and metalaxyl (Subdue) for pythium control at 2 fl oz product/1,000 sq ft on 26 July and 11 August; ii) curative application of aforementioned fungicides when disease was observed as active; and iii) untreated. Fungicide sub-subplots measured 2 X 4 m.
Data collection:
a) Weed infestation: Weed density was determined once weekly (eight dates) by randomly dropping a 30 by 30-cm template at three locations in each sub-subplot. The numbers of grassy and broadleaf weeds in the template area were counted.
b) Disease infestation: Brown patch incidence was rated in each sub-subplot weekly (eight dates) using a visual estimate of percent infestation. Leaf spot also appeared in plots in late summer.
c) Clipping collection: Clippings were collected weekly by making one lengthwise pass in each sub-subplot with a push-type reel mower. Clippings were dried and weighed..
d) Turf quality: Visual turf quality was rated on three occasions during the study period in each sub-subplot.
e) Total water applied. Irrigation treatments were compared to determine water saved by monitoring ET. Depth of water (cm) applied weekly was determined from irrigation run times.
f) Total pesticide applied. Pesticide need as influenced by irrigation treatment was determined. Number of pesticide applications and total amount of active ingredient were determined.
Analysis of variance and single degree of freedom contrasts were used to determine treatment effects.
RESULTS:
A total of 18.6 inches of water was applied to daily irrigated turf, whereas turf irrigated to replace ET received 6.2 inches. Total active ingredient applied in the preventive program was 14.1 lbs a.i./a, whereas 14.0 lbs a.i./a was applied in the curative program. Hence, in this situation, there was no real environmental advantage of applying pesticides curatively vs. preventively (without considering chemical properties of pesticides used). Where the potential for weed or disease infestation is lower, a curative program might have an advantage in this regard. Furthermore, curative applications often are made to localized areas that would reduce the total amount of pesticide required compared to a blanket application that might be used in a preventive program.
Better turf quality and 9% less disease were observed in perennial ryegrass irrigated daily (Table 1). Daily irrigation reduced disease regardless of fungicide treatment. Over irrigation usually is related to greater disease. Turf in plots irrigated to replace ET often exhibited some wilt during midday when temperatures were over 80 F. Infected plants in daily irrigated plots seemed less likely to die than those in plots irrigated to replace ET.
Greater disease (primarily leaf spot) was observed in plots that received the curative herbicide treatment (fexoxaprop plus 2,4-D + dicamba + mecoprop). Research in Texas also has
suggested that phenoxy herbicides can predispose plants to leaf spot infection.
Fungicides reduced diseased area by about 13% (Table 1). About 3% greater disease occurred where a curative fungicide treatment was used vs. a preventive treatment. This is not unusual, for some degree of infestation must be present before the need for a curative treatment is recognized.
These results suggest that daily irrigation or fungicides can be used to suppress brown patch and leaf spot diseases on perennial ryegrass fairways. Least disease occurred in daily irrigated plots treated preventively with fungicides. In these studies, only excessive irrigation (0.3 inches per day) was evaluated. More work is required to evaluate daily irrigation to replace ET and resulting effects on disease. Daily irrigation has detriments that were not evaluated, including the potential for reduced turfgrass rooting, inability of the plant to effectively acclimate to drought conditions, and greater soil compaction. This work will continue in 1996.
Table 1. Effect of irrigation and curative and preventive herbicide and fungicide treatments on ryegrass turf response and pest incidence.
| Contrast | Turf Quality (0 to 9) | Clipping Weight (g/m2) | Disease (% of Plot Area) | Broadleaf Weeds (no./m2) | Crabgrass (no./ m2) |
| Daily irrigation vs. Irrigation to replace ET | 8.3
| 1.6
| 11.7
| 3.8
| 3.7
|
| Nontreated vs. Herbicide treated | 8.0 7.8 | 1.6 1.2 | 14.3 17.3 | 6.1 2.1* | 11.6 1.2 |
| Herbicide curative vs. Herbicide preventive | 7.5 8.1** | 1.0 1.5 | 20.6 14.0** | 1.3 2.8 | 1.0 1.4 |
| Nontreated vs. Fungicide treated | 7.6 8.0*** | 1.2 1.4 | 25.0 11.9*** | 2.7 3.7 | 4.4 4.7
|
| Fungicide curative vs. Fungicide preventive | 8.0 8.0 | 1.3 1.6 | 13.7 10.2* | 2.9 4.6** | 4.9 4.6 |