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© 2007 Plant Management Network.
Accepted for publication 30 July 2007. Published 21 September 2007.

Comparison of Irrigation Systems and Fungicide Programs in Virginia Market-type Peanut

David L. Jordan and P. Dewayne Johnson, Professor and Research Technician III, Department of Crop Science, Box 7620, North Carolina State University, Raleigh 27695

Corresponding author: David L. Jordan. David_Jordan@ncsu.edu

Jordan, D. L., and Johnson, P. D. 2007. Comparison of irrigation systems and fungicide programs in Virginia market-type peanut. Online. Crop Management doi:10.1094/CM-2007-0921-01-RS.

Abstract

Research was conducted in North Carolina to determine interactions of irrigation and fungicide program on canopy defoliation caused by early leaf spot (Cercospora arachidicola Hori) and web blotch (Phoma arachidicola Marasas et al.), pod yield, and percentages of extra large kernels (%ELK), fancy pods (%FP), and total sound mature kernels (%TSMK) for the Virginia market type peanut cultivar Gregory. Irrigation treatments included no irrigation, subsurface drip irrigation (SDI), overhead sprinkler irrigation (OSI), and a combination of SDI and OSI. Fungicide programs included no fungicide or bi-weekly applications beginning in early July through mid- September. Bi-weekly fungicide applications decreased canopy defoliation (P ≤ 0.0001), increased pod yield (P ≤ 0.0001), %ELK (P ≤ 0.0001), and %FP (P = 0.0166) but did not affect %TSMK (P = 0.1603) when compared with the no-fungicide control. Irrigation did not affect canopy defoliation (P = 0.3788) but did affect pod yield (P = 0.0878), %ELK (P = 0.0021), %FP (P = 0.0031), and %TSMK (P = 0.0702). The %ELK was similar when peanut was not irrigated (48%) or was irrigated with SDI only (46%) and the combination of SDI and OSI (48%). The highest %ELK was noted when with OSI only (52%). Irrigation increased %FP regardless of irrigation system compared with non-irrigated peanut (84% versus 87 to 90%).

Introduction

The percentage of irrigated peanut in the United States increased from as little as 10% in the 1970s to almost 50% in the 1990s (9). Less than 20% of peanut hectares are irrigated in North Carolina (7). Approximately 44% of peanut hectares are irrigated in the southwestern United States (1). Overhead sprinkler irrigation (OSI) is the primary method of irrigation of peanut (14). However, more recently some growers have adopted subsurface drip irrigation (SDI) in peanut and other agronomic and vegetable crops (14,19). Subsurface drip irrigation can conserve soil water and provide peanut yield similar to that of peanut grown under OSI (10,13). Cost of installation of SDI and OSI depends on field size, topography, and cropping systems (1,2,14). Long-term investment in either system is similar (14).

Defoliation of peanut caused by early leaf spot was lower when peanut was grown under SDI compared with OSI (10). Less defoliation due to lower incidence of early leaf spot was associated with a decrease in the amount and duration of moisture in the peanut canopy under SDI compared with OSI. Increased humidity in the peanut canopy and moist soil conditions following OSI can increase incidence of Sclerotinia blight (caused by Sclerotinia minor Jagger), early leaf spot, and late leaf spot [caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton syn. Phaeoisariopsis personata von Arx] (12,15,21). Disease incidence often increases under irrigation, and benefits of increased yield can be minimized due to increased incidence of non-controlled disease (12,15,21). Less disease, more efficient water use, and maintenance of pod yield make SDI an attractive alternative to OSI.

Sorensen et al. (19) reported higher yield of the runner market type cultivar Georgia Green when at least two years separated peanut in the same field, SDI was spaced 91 cm apart, and peanut was irrigated at 75% of estimated crop use compared with yield of continuous peanut, SDI spaced 182 cm apart, and irrigation at 50% of estimated crop use. While SDI provided sufficient soil moisture to promote growth of the peanut plant, soil moisture with SDI was limited in the pegging zone (18,19). Calcium movement into developing pegs and maturing pods is influenced by soil moisture, and lower %ELK values are often associated with sub-optimal calcium absorption by these structures (6,7). Lanier et al. (10) reported that although pod yield of the Virginia market type cultivar Perry was similar when peanut was grown under SDI and OSI, a lower %ELK was noted in SDI compared to OSI in one of two years. Sorensen and Wright (18) suggested that SDI maintained soil temperatures in the pegging zone below a critical value of 29°C (4) from peanut fruit initiation through crop harvest. A ceiling for the critical value for soil temperature has not been established for Virginia market type peanut. Additionally, research has not been conducted to determine the combined effects of SDI and OSI on pod yield and market grade characteristics.

Determining interactions among irrigation systems and disease management programs is important in developing efficient production and pest management recommendations for peanut. Research was conducted to compare canopy defoliation caused by early leaf spot and web blotch, peanut pod yield, and percentages of ELK, FP, and TSMK when rainfall was supplemented with SDI, OSI, and a combination of SDI and OSI compared with no irrigation when fungicides were applied bi-weekly or not at all.

Studying Interaction of Irrigation and Fungicide Program in Peanut

The experiment was conducted in North Carolina during 2003 and 2004 at the Peanut Belt Research Station located near Lewiston-Woodville on a Norfolk sandy loam (fine-loamy, siliceous, thermic, Typic Paleudults) with pH 6.1 and 2.3% organic matter. Peanut cultivar Gregory was seeded at 140 kg/ha in single rows spaced 91 cm apart on 5 May 2003 and 8 May 2004. This seeding rate was designed to establish 14 plants per linear m of row (7). Aldicarb was applied in the seed furrow at 1.1 kg ai/ha. With the exception of fungicides applied for disease control and irrigation, all other production and pest management inputs were common across the entire test area and were based on North Carolina Cooperative Extension Service recommendations (3,7,8,17).

Experimental design and treatment factors. The experimental design was a split-plot in a two-factor factorial arrangement including four irrigation methods and two fungicide programs. Irrigation was the whole plot unit and fungicide program was the sub-plot unit. Irrigation treatments included no irrigation, SDI, OSI, and a combination of SDI and OSI. Fungicide programs included no fungicide and bi-weekly applications beginning in early July through mid-September (Table 1). Individual sub-plot treatment size was four rows by 9 m long. Sub-plots were replicated four times.

Table 1. Fungicides and application dates for the bi-weekly spray programs during 2003 and 2004.

 * Chlorothalonil, pyraclostrobin, and tebuconazole were applied at 1200, 175, and 230 g/ha, respectively.

Irrigation installation and application. In early April 2001, soil was disked twice and field cultivated to prepare the field for installation of SDI. Drip tubing was installed with a ripper-bedder at a depth of 25 cm in rows spaced 91 cm apart. Beds were established each year in non-irrigated and OSI plots with a disk bedder equipped with in-row ripper shanks (ripping depth of 25 cm). Beds in the SDI blocks of the field were re-established in 2003 following peanut in 2001 and cotton in 2002 (10). Similarly, peanut in 2004 followed peanut in 2002 and cotton in 2003 (10). Beds were prepared without ripping in SDI. Water was pumped from an irrigation pond to a 22,710-liter reservoir tank, which supplied water for both irrigation systems. Water from the reservoir tank was supplied with a centrifugal pump (Challenger 1.5 kW Water Pump, Model 35-5460, Pentair Pool Products, St. Paul, MN) through a sand filter system (Flow Guard Sand Filter System, Model 215S, Flow Guard Filtration Products, Selma, CA) and through a disk filtration system [ARKAL Disk Filter (140 mesh by 100 micron), Netafim, Tel Aviv, Israel] to remove fine particulates. Filtered water flowed through the main manifold to drip lines in respective blocks. Control of water application was regulated by an electric water control console valve and electronic solenoid (Orbit Electric Water Control, Model 57540, Orbit Irrigation Products Inc., Bountiful, UT). Flow meters (ABA Flow Meters, 16 mm by 19 mm, Model 98604940, Senniger Irrigation Inc., Orlando, FL) were used to measure flow rates and record water application in SDI. Pressure regulators followed the flow meters to reduce pressure to 69 kPa. Drip tubing used for SDI was model TSX2 510-12-450 (T-Tape, T-Systems Inc., Queensland, Australia) and was 25 mm in diameter with emitters spaced at 30 cm. The SDI system was designed to deliver 102 liters/min.

The OSI irrigation system consisted of six irrigation heads spaced 6.1 m apart (OSI System 20H, Nelson Irrigation Sprinkler Heads, Walla Walla, WA) established on a single irrigation line placed down the middle of each block of OSI plots. Water use in OSI was recorded with Taylor model 2715 (Taylor USA, Oak Brook, Illinois) rain gauges. A series of 10 rain gauges were spaced equally through the radius of sprinkler nozzle on either side of OSI pipe. Frequency and amount of irrigation was based on recommendations from the Irrigator Pro model for peanut (5). Overhead sprinkle irrigation was supplied as sequential applications of 18 mm to satisfy irrigation requirements. Irrigation was done during the morning hours to avoid wind and optimize water distribution. A total of 138 and 112 mm water was provided by OSI during 2003 and 2004, respectively (Table 2). In these respective years, 127 and 125 mm water was applied through SDI during the season from early July and mid-September (Table 2). Rainfall during this period was 504 mm (2003) and 510 mm (2004) (Table 2). Water was applied each day with SDI from Monday through Friday at a rate of approximately 5 mm/day as needed to satisfy recommendations from Irrigator Pro (5). Irrigation was reinitiated 4 days after rainfall in excess of 18 mm and was continued when rainfall events were less than 18 mm.

Table 2. Rainfall and water supplied through subsurface drip irrigation (SDI), overhead sprinkler irrigation (OSI), and the combination of SDI and OSI during 2003 and 2004.

Data collected and statistical analyses. The percentage of the peanut canopy that was defoliated by the combination of early leaf spot and web blotch was determined in late September within one week prior to digging and inverting peanut vines using a scale of 0 to 100% where 0 = no defoliation and 100 = complete defoliation (10). Peanut was dug and vines inverted based on pod mesocarp color determination (16,20). A composite sample of four plants from two replications within each irrigation treatment where fungicide was applied bi-weekly was used to determine when to initiate digging peanut. Pod maturity was similar under all irrigation systems, allowing digging of peanut for all irrigation systems to occur on the same day. Peanut was harvested after pods and vines were allowed to air dry for approximately 1 week. A 1-kg sample of pods was collected at harvest from each plot to determine %ELK, %FP, and %TSMK using Cooperative Grading Service criteria (Peanut Loan Schedule, 1997-2001, USDA-FSA-1014-3).

Data for canopy defoliation, pod yield, %ELK, %FP, and %TSMK were subjected to analysis of variance appropriate for a two (year) by four (irrigation system) by two (fungicide program) factorial treatment arrangement in a split plot design. Means of significant main effects and interactions were separated using Fisher’s Protected LSD test at P ≤ 0.10 using appropriate error terms for fixed and random effects for the split plot treatment arrangement (11).

Canopy Defoliation, Pod Yield, & Market Grade Characteristics

Interactions of year × irrigation × fungicide program, irrigation × fungicide program, and year × irrigation were not significant (P ≤ 0.05 or P ≤ 0.10) for canopy defoliation, pod yield, %ELK, %FP, and %TSMK (Table 3). However, the interaction of year × fungicide program was significant for canopy defoliation (P ≤ 0.0001) (Table 3). Although this interaction was not significant for pod yield and market grade characteristics, the main effect of fungicide program was significant (P ≤ 0.0001) for canopy defoliation, pod yield, %ELK, and %FP. The main effect of irrigation was significant for pod yield (P = 0.0878), %ELK (P = 0.0021), %TSMK (P = 0.0702), and %FP (P = 0.0031) (Table 3).

Table 3. Analyses of variance for canopy defoliation caused by early leaf spot and web blotch; pod yield; and percentages of extra large kernels (%ELK), fancy pods (%FP), and total sound mature kernels (%TSMK).

 ^a indicates significance at P ≤ 0.05.

 ^b indicates significance at P ≤ 0.10.

Table 4. Canopy defoliation, pod yield, and percentages of extra large kernels (%ELK), fancy pods (%FP), and total sound mature kernels (%TSMK) when fungicides were applied bi-weekly compared with non-treated peanut.

 * indicates significance at P ≤ 0.05. Data are pooled over years and irrigation treatments.

When pooled over years and irrigation treatments, canopy defoliation was 91% and 75% within 1 week of digging when fungicides were not applied during 2003 and 2004, respectively (Table 4). In contrast, canopy defoliation was 5% or less during 2003 and 2004 when fungicides were applied bi-weekly (Table 4). When pooled over years and irrigation treatments, pod yield increased from 1260 to 3020 kg/ha when fungicides were applied compared to pod yield of the no-fungicide control (Table 4). When fungicides were applied bi-weekly, %ELK and %FP increased from 44 to 53% and 86 to 88%, respectively (Table 4). The %TSMK ranged from 73 to 74% and was not affected by fungicide program (Tables 3 and 4). Increased pod yield, %ELK, and %FP following application of fungicide were not surprising. Preventing canopy defoliation has been shown to increase pod yield and improve market grades compared with non-treated peanut or peanut with sub-optimum foliar disease control (17).

There was no difference in canopy defoliation when comparing irrigation treatments (Tables 3 and 5). Canopy defoliation ranged from 42 to 45% when pooled over years and fungicide programs (Table 5). Peanut pod yield was not affected by irrigation during these experiments at P ≤ 0.05 (Table  3). However, when comparing means (P = 0.0878) pooled over years and fungicide programs, pod yield was higher with the combination of OSI and SDI than SDI alone or non-irrigated peanut (Table 5). Pod yield did not differ when comparing OSI and SDI alone or SDI and non-irrigated peanut (Table 5).

Table 5. Peanut canopy defoliation, pod yield, and percentages of extra large kernels (%ELK), fancy pods (%FP), and total sound mature kernels (%TSMK) response to subsurface drip irrigation (SDI), overhead sprinkler irrigation (OSI), and the combination of OSI and SDI.

 * Means followed by the same letter are not significant different according to Fisher’s Protected LSD. Data are pooled over years and fungicide treatments.

The %ELK was similar when peanut was not irrigated (48%) or was irrigated SDI only (46%) and the combination of SDI and OSI (48%). The highest %ELK was noted when with OSI only (52%) (Table 5). The %FP was higher when peanut was subjected to OSI compared with SDI or no irrigation (Table 5). However, there was no difference in %FP when comparing peanut irrigated with OSI or a combination of OSI and SDI (Table 5).

The cultivar Gregory produces the largest kernels and pods when compared with other commercially planted Virginia market type peanut in North Carolina, and calcium is essential for adequate development of pods for this cultivar (7). Higher %ELK and %FP is indicative of larger pods (7), and although not documented in this research, presence of water in the pegging zone from OSI may have contributed to higher levels of calcium moving into pods compared with less soil water in the pegging zone for SDI only (18). This explanation does not, however, address the lower %ELK noted when peanut was subjected to the combination of SDI and OSI (48%) compared with OSI only (52%). It is plausible that the combination of OSI and SDI provided excess soil water that may have adversely affected overall peanut growth or pod development irrespective of calcium movement into developing pods. Previous research (10) indicated that %ELK, %FP, and %TSMK was higher when peanut was subjected to OSI compared with SDI in one of two experiments.

A total of 504 and 510 mm of rain was documented during 2003 (2 July through 12 September) and 2004 (15 July through mid-10 September), respectively (Table 2). Lanier et al. (10) reported a positive response to SDI and OSI compared with non-irrigated peanut when disease was controlled in years when peanut received 120 to 185 mm rainfall. In their experiments, pod yield increased from 2540 kg/ha (non-irrigated) to 3360 kg/ha (OSI) and 3560 kg/ha (SDI). In our experiment, pod yield increased from 1960 kg/ha for non-irrigated peanut to 2200 kg/ha (OSI) and 2330 kg/ha (combination of OSI and SDI) when pooled over years and fungicide programs (Table 5). When comparing pod yield following fungicide applications, which is the comparison of Lanier et al. (10), pod yield for non-irrigated peanut, SDI, OSI, and the combination of OSI and SDI was 2810, 3030, 3040, and 3210 kg/ha, respectively (data not shown). Less rainfall during experiments by Lanier et al. (10) compared with more rainfall in our experiments may explain the more modest response to irrigation reported here.

Consistent with previous findings (10), results from this experiment demonstrate that %ELK and %FP may be lower when peanut is grown under SDI compared with OSI. Additionally, the combination of OSI and SDI was less effective in maintaining %ELK than OSI alone. Concern about pod and kernel development in SDI has been expressed previously because this approach to irrigation may limit water in the pegging zone (10,18). Results from these experiments also reinforce the importance of effective fungicide programs to control foliar disease in peanut, which minimizes pod shed and maintains optimum pod yield and market grades. However, differential response to fungicide treatment (no fungicide versus bi-weekly sprays) was not observed when comparing irrigation systems. This is in contrast to previous results (10) demonstrating less canopy defoliation when fungicides were not applied and peanut was planted with SDI compared with OSI. The discrepancy may have been associated with previous crop rotation and development of disease in combination with rainfall, relative humidity, and temperature during these years with respect to establishment of disease epidemics. Crops other than peanut were planted in these fields prior to planting peanut in 2001 and 2002 (10). However, only one year of cotton separated peanut plantings in our experiment. It is possible that the level of inoculum produced during the previous peanut crop due to no-fungicide controls dwarfed any minor differences in foliar disease development that may have been present when comparing irrigation treatments.

Acknowledgments

The North Carolina Peanut Growers Association Inc. and the North Carolina Agricultural Foundation provided partial funding for this research. Appreciation is expressed to Steve Barnes and Tommy Corbett, former and current Research Station Superintendents, and Jimmy Matthews, Derrick Ambrose, Joel Alston, David Callus, Greg Hughes, James Roundtree, and Reginald Wilkins, former and current technical staff at the Peanut Belt Research Station, North Carolina Department of Agriculture and Consumer Services, for assistance with these experiments. Carl Murphy assisted with harvest and determining market grades.

Literature Cited

1. Bosch, D. J., Powell, N. L., and Wright, F. S. 1998. Investment returns from three sub-surface microirrigation tubing spacings. J. Prod. Agric. 11:371-376.

2. Bosch, D. J., Powell, N. L., and Wright, F. S. 1992. An economic comparison of subsurface microirrigation with center pivot sprinkler irrigation. J. Prod. Agric. 5:431-436.

3. Brandenburg, R. L. 2007. Peanut insect management. Pages 75-93 in: 2007 Peanut Information. Series AG-331, N. Car. Coop. Ext. Serv., Raleigh, NC.

4. Davidson, J. L., Jr., Blankenship, P. D., Henning, R. J., Guerke, W. R., Smith, R. D., and Cole, R. J. 1991. Geocarposphere temperature as it relates to Florunner peanut production. Peanut Sci. 18:79-85.

5. Davidson, J. L., Jr., Griffin, W. J., Lamb, M. C., Williams, R. G., and Sullivan, G. 1998. Validation of Exnut for scheduling peanut irrigation in North Carolina. Peanut Sci. 25:50-58.

6. Gascho, G. J., and Davis, J. G. 1995. Soil fertility and plant nutrition. Pages 383-418 in: Advances in Peanut Science. H. E. Pattee and T. H. Stalker, eds. Am. Peanut Res. and Educ. Soc., Stillwater, OK.

7. Jordan, D. L. 2007. Peanut production practices. Pages 23-46 in: 2007 Peanut Information. Series AG-331, N. Car. Coop. Ext. Serv., Raleigh, NC.

8. Jordan, D. L. 2007. Peanut weed management. Pages 47-74 in: 2007 Peanut Information. Series AG-331, N. Car. Coop. Ext. Serv., Raleigh, NC.

9. Lamb, M. C., Davidson, J. L., Jr., Childre, J. W., and Martin, N. R., Jr. 1997. Comparison of peanut yield, quality, and net returns between non-irrigated and irrigated production. Peanut Sci. 24:97-101.

10. Lanier, J. E., Jordan, D. L., Barnes, J. S., Matthews, J., Grabow, G. L., Griffin, W. J., Jr., Bailey, J. E., Johnson, P. D., Spears, J. F., and Wells, R. 2004. Disease management in overhead and subsurface drip irrigation systems for peanut. Agron. J. 96:1058-1065.

11. McIntosh, M. S. 1982. Analysis of combined experiments. Agron. J. 75:153-155.

12. Porter, D. M., and Wright, F. S. 1987. Effects of sprinkler irrigation on peanut diseases in Virginia. Plant Dis. 71:512-514.

13. Puppala, N., Baker, R. D., and Sorensen, R. B. 2000. Valencia peanut yield response to subsurface drip vs. center pivot irrigation systems. Proc. Am. Peanut Res. Ed. Soc. 32:34.

14. O’Brien, D. M., Rogers, D. H., Lamm, F. R., and Clark, G. A. 1998. An economic comparison of subsurface drip and center pivot sprinkler irrigation systems. Appl. Engin. Agric 14:391-398.

15. Rotem, J., and Palti, J. 1969. Irrigation and plant diseases. Ann. Rev. Phytopathol. 7:267-288.

16. Sholar, J. R., Mozingo, R. W., and Beasley, J. P., Jr. 1995. Peanut cultural practices. Pages 354-382 in: Advances in Peanut Science. H. E. Pattee and H. T. Stalker, eds. Am. Peanut Res. Educ. Soc. Inc., Stillwater, OK.

17. Shew, B. 2007. Peanut disease management. Pages 94-188 in: 2007 Peanut Information. Series AG-331, N. Car. Coop. Ext. Serv., Raleigh, NC.

18. Sorensen, R. B., and Wright, F. S. 2002. Soil temperature in the peanut pod zone with subsurface drip irrigation. Peanut Sci. 29:115-122.

19. Sorensen, R. B., Butts, C. L., and Rowland, D. L. 2005. Five years of subsurface drip irrigation on peanut: what have we learned? Peanut Sci. 32:14-19.

20. Williams, E. J., and Drexler, J. S. 1981. A non-destructive method for determining peanut pod maturity. Peanut Sci. 8:134-141.

21. Wright, F. S., Porter, D. M., Powell, N. L., and Ross, B. B. 1986. Irrigation and tillage effects on peanut yield in Virginia. Peanut Sci. 13:89-92.