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PRODUCTION PAPER

Disease Management in Overhead Sprinkler and Subsurface Drip Irrigation Systems for Peanut

^a Dep. of Crop Sci., North Carolina State Univ., Box 7620, Raleigh, NC 27695-7620
^b Peanut Belt Res. Stn., North Carolina Dep. of Agric. and Consumer Serv., 112 Research Station Lane, Lewiston-Woodville, NC 27849-0220
^c Dep. of Biol. and Agric. Eng., North Carolina State Univ., Box 7637, Raleigh, NC 27695-7637
^d North Carolina Coop. Ext. Serv., 102 Dundee St., Windsor, NC 27983
^e Dep. of Plant Pathol., North Carolina State Univ., Box 7616, Raleigh, NC 27695-7616

^* Corresponding author (david_jordan{at}ncsu.edu).

Received for publication July 25, 2003.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Experiments were conducted during 2001 and 2002 at one location in North Carolina to compare development of early leaf spot (Cercospora arachidicola Hori), pod yield, and market grade characteristics when peanut (Arachis hypogea L.) was grown under overhead sprinkler irrigation (OSI) and subsurface drip irrigation (SDI) and fungicides were not applied or applied biweekly or based on weather advisories. Incidence of early leaf spot was lower when peanut was grown under SDI compared with OSI when fungicides were not applied. Fewer fungicide applications were needed when applications were based on weather advisories rather than when applied biweekly. There was no difference in early leaf spot control or leaf defoliation resulting from disease when fungicides were applied regardless of irrigation system or fungicide application approach. Pod yield was higher in 2001 under SDI compared with OSI when fungicides were not applied; yield was similar in 2002. Disease severity was much higher in 2001 than in 2002 and most likely explains differences in pod yield between years. No difference in yield was noted when fungicides were applied, regardless of irrigation system. The percentage of extra large kernels (%ELK) was lower in 1 of 2 yr under SDI compared with OSI. There were no differences in percentages of fancy pods (%FP), sound splits (%SS), and other kernels (%OK) among irrigation systems and fungicide programs. In a separate experiment where fungicides were applied biweekly, pod yield, %FP, and %ELK were similar under SDI and OSI but greater than nonirrigated peanut. The %OK was lower when peanut was irrigated.

Abbreviations: OSI, overhead sprinkler irrigation • SDI, subsurface drip irrigation • %ELK, percentage of extra large kernels • %FP, percentage of fancy pods • %OK, percentage of other kernels • %SS, percentage of sound splits • %TSMK, percentage of total sound mature kernels

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
THERE ARE APPROXIMATELY 195615 ha of irrigated peanut in the southeastern United States (Lamb et al., 1997). The percentage of irrigation has increased from less than 10% in the 1970s to more than 49% in the 1990s (Lamb et al., 1997). In North Carolina, less than 20% of peanut acreage is irrigated (Jordan, 2003). In the southwestern United States, 44% of peanut acreage is irrigated (Bosch et al., 1998). In these regions, OSI is the primary method (O'Brien et al., 1998). Irrigation generally increases peanut yield when disease is controlled (Porter and Wright, 1987). However, disease incidence often increases under irrigation, and benefits of increased yield can be minimized due to increased incidence of noncontrolled disease (Rotem and Palti, 1969; Wright et al., 1986). Increased moisture on the soil surface and humidity in the peanut canopy following overhead irrigation can increase incidence of Sclerotinia blight (Sclerotinia minor), pod rot (Pythium myriotylum), and leaf spots (Cercospora arachidicola and Cercosporidium personatum) (Wright et al., 1986).

Subsurface drip irrigation has been evaluated in a variety of agronomic and vegetable crops (O'Brien et al., 1998). Subsurface drip irrigation can conserve water while maintaining or increasing peanut yield (Puppala et al., 2000). It is suspected that disease incidence in peanut would be lower under SDI compared with OSI because a decrease in the amount and duration of moisture in the canopy under SDI would lessen the likelihood of disease development. Cost of installation of SDI and OSI depends upon field size, topography, and cropping systems (Bosch et al., 1992; O'Brien et al., 1998). Initial and long-term investment in either system is similar (O'Brien et al., 1998). Less disease and more efficient water use make SDI an attractive alternative to OSI. In North Carolina, peanut is grown on relatively small and irregular-shaped fields that limit efficient use of OSI.

Peanut producers in the United States apply a wide range of fungicides to control foliar and soil-borne diseases (Shew, 2003). Although many peanut producers apply fungicides biweekly, advisories have been developed to more precisely time applications (Bailey, 1999). This approach to disease management uses temperature and relative humidity to establish a threshold for development of early leaf spot and other diseases (Bailey, 1994, 1999). Using weather-based advisories to target fungicides for early leaf spot control can reduce the number of fungicide sprays needed for adequate disease control (Bailey, 1999; Damicone et al., 1994; Jordan et al., 1999).

Although the majority of peanut in the United States is seeded in single rows spaced 91 to 100 cm apart, research suggests that seeding peanut in twin row patterns (rows spaced approximately 18 cm apart with centers between the twin rows spaced 91 to 100 cm apart) can increase yield, improve some market grade characteristics, and decrease incidence of tomato spotted wilt tospovirus (Baldwin and Williams, 2002). However, increased incidence of other diseases and poorer row visibility at the time of digging and inversion of peanut vines have been observed in twin row-planting patterns (Beasley, 1970; Henning et al., 1982).

Determining interactions among irrigation systems and disease management programs will assist in developing efficient production and pest management systems for peanut. Research was conducted to compare early leaf spot control, peanut pod yield, and market grade characteristics when peanut was grown under SDI and OSI and fungicides were applied biweekly or based on weather advisories. Additional research was conducted to compare peanut pod yield and market grade characteristics when peanut was grown under SDI and OSI compared with nonirrigated peanut when fungicides were applied biweekly.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Peanut Response to Subsurface Drip Irrigation and Overhead Sprinkler Irrigation under Various Disease Management Programs
Experiments were conducted in 2001 and 2002 in North Carolina 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. In early April 2001, soil was disked twice and field-cultivated to prepare the field for installation of drip irrigation lines. Irrigation lines were installed with a ripper-bedder at a depth of 25 cm in rows spaced 91 cm apart. Corn (Zea mays L.) was planted in 2000 before installing irrigation lines during February 2001. The experiment with peanut was established in half of the field. Cotton (Gossypium hirsutum L.) was planted in the remaining portion of the field 2001. In 2002, peanut was planted in the portion of the field where cotton was planted in 2001. Beds were established during both years in OSI with a disk bedder equipped with in-row ripper shanks (ripping depth of 25 cm). Beds in the SDI area of the field were re-established in 2002 using a bedder without ripper shanks. Water was pumped from an irrigation pond to a reservoir tank to supply the SDI plots with irrigation. Water from the reservoir tank was supplied with a centrifugal propeller water pump (Challenger 1.5 kW Water Pump, Model 35-5460, Pentair Pool Products, St. Paul, MN) to a sand filter system (Flow Guard Sand Filter System, Model 215S, Flow Guard Filtration Products, Selma, CA), and then to disk filtration system [ARKAL Disk Filter (140 mesh by 100 µm), Netafim, Tel Aviv, Israel] to remove fine particles from irrigation water. Water then flowed to an irrigation manifold that supplied water to specific plots. Irrigation water scheduling to plots was controlled by an electric water control console and electric solenoids (Orbit Electric Water Control, Model 57540, Orbit Irrigation Products, Inc., Bountiful, UT). Flow meters (ABA Flow Meters, 16 by 19 mm, Model 98604940, Sennniger Irrigation, Inc., Orlando, FL) were used to measure flow rates. Pressure regulators followed the flow meters to reduce pressure to 69 kPa. Irrigation water then flowed in 25-mm supply lines buried 25 cm below the ground surface with emitters spaced 30 cm apart delivering 102 L m^–1 (TSX2 510-12-450 T-Tape, T-Systems, Inc., Queensland, Australia). Subsurface drip irrigation was calibrated to supply 5 mm d^–1, a rate for SDI established previously for peanut (Stansell et al., 1976). The OSI system consisted of six irrigation heads spaced 6.1 m apart (OSI System 20H, Nelson Irrigation Sprinkler Heads, Walla Walla, WA) and established on a single irrigation line placed down the middle of the OSI. A total of 18 mm of water for the OSI treatment was applied over 45 min from the same water source used for SDI. Frequency and amount of irrigation were based on recommendations from the Irrigator Pro model (Davidson et al., 1998). This system uses thermal data from probes established 5 cm below the soil surface to initiate irrigation. Overhead sprinkler irrigation was supplied as sequential applications of 18 mm on consecutive days. Irrigation was applied during the morning when wind speed was low to avoid movement to adjacent plots. The amount of rainfall and total irrigation for both SDI and OSI are presented in Fig. 1 . A total of 156 and 155 mm was provided by OSI in 2001 and 2002, respectively. In these respective years, 153 and 154 mm was provided by SDI during the season. Average daily air temperature and relative humidity were recorded from a stationary weather station 1.5 m above ground located 200 m from the test site (Fig. 2 and 3) . Subsurface drip irrigation was applied each day from Monday through Friday at a rate of 2 mm d^–1. Subsurface drip irrigation was reinitiated 4 d after rainfall in excess of 18 mm and was continued when rainfall was less than 18 mm.

View larger version (17K): [in this window] [in a new window]   Fig. 1. Rainfall and irrigation at Lewiston-Woodville during 2001 and 2002.

View larger version (23K): [in this window] [in a new window]   Fig. 2. Average daily air temperature from 1 May through 1 October at Lewiston-Woodville during 2001 and 2002.

View larger version (21K): [in this window] [in a new window]   Fig. 3. Average daily relative humidity at Lewiston-Woodville during 2001 and 2002.

The percentage of peanut leaflets with early leaf spot lesions present in mid-September was recorded on a scale of 0 to 100% where 0 = no lesions and 100 = all leaflets with at least one lesion present. The percentage of the peanut canopy that was defoliated by early leaf spot was determined in late September using a scale of 0 to 100% where 0 = no defoliation and 100 = complete defoliation of the peanut canopy. Percentage of plants exhibiting symptoms characteristic for tomato spotted wilt virus (Shew, 2003) was determined using a scale of 0 (no symptoms) to 100 (each 30-cm section of row exhibiting symptoms). Peanut was dug and vines inverted based on pod mesocarp color (Williams and Drexler, 1981). Pod mesocarp colors of brown and black indicate that kernels are more advanced in maturity than pods showing mesocarp colors of orange, yellow, or white. Pod maturity was similar under both irrigation systems, allowing digging of peanut for both irrigation systems to occur on the same day. Peanut was combined after pods and vines were allowed to air-dry for approximately 1 wk. A 1-kg sample of pods was collected at harvest from each plot to determine %FP, %ELK, %SS, percentage of total sound mature kernels (%TSMK), and %OK using Cooperative Grading Service criteria (Peanut Loan Schedule, 1997–2001, USDA-FSA-1014-3). Economic value ($ ha^–1) was calculated as the product of pod yield and market value ($ kg^–1) of farmer stock peanut using the loan rate of $0.43 kg^–1, including premiums and discounts based on market grade criteria (USDA Notice PS-479).

Data were subjected to analysis of variance appropriate for a two (year) by two (irrigation system) by four (disease management program) factorial treatment arrangement. Means of significant main effects and interactions were separated using Fisher's Protected LSD test at p 0.05 using appropriate error terms for fixed and random effects for the split-plot treatment arrangement (McIntosh, 1982).

Comparison of Irrigated and Nonirrigated Systems
The experiment was conducted during 2001 and 2002 at Lewiston-Woodville in the same field described previously. Irrigation systems for SDI and OSI also were established as described previously. The peanut cultivar Perry was seeded in single rows at a spacing of 91 cm at a seeding rate of 140 kg ha^–1. In addition to SDI and OSI irrigation, a no-irrigation control was included. Fungicides were applied biweekly as described previously to maintain peanut free of early leaf spot (Tables 1 and 2). Peanut was dug and vines inverted on the same day in 2001, based on pod mesocarp color. In 2002, peanut was dug and vines inverted 1 wk earlier under SDI and OSI than nonirrigated peanut based on pod mesocarp color determination.

The experimental design was a randomized complete block with irrigation treatments replicated four times. Data for pod yield, market grade characteristics, and economic value were subjected to analysis of variance. Means were separated using Fisher's Protected LSD test at p 0.05.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Peanut Response to Subsurface Drip Irrigation and Overhead Sprinkler Irrigation under Various Disease Management Programs
The interaction of year x irrigation system x disease management program was significant for early leaf spot incidence (Table 3). When analyzed by year, the interaction of irrigation x disease management program was significant during both years (Table 4). This interaction was most likely caused by differences in severity of early leaf spot for the 2 yr as observed in the no-fungicide controls for both irrigation systems (Table 5). It is suspected that higher rainfall in 2001, especially earlier in the season, may have contributed to greater incidence of early leaf spot during 2001 compared with 2002 (Fig. 1). Irrigation was generally applied early in the morning, giving foliage ample time to dry during the day. Although not clearly established in the climatic data, high temperature and somewhat low relative humidity in general may have contributed to there being less early leaf spot in 2002 compared with 2001 when fungicides were not applied (Table 5 and Fig. 2 and 3).

In both SDI and OSI, six fungicide applications were made in the biweekly approach (Tables 1 and 2). In contrast, four fungicide applications were made when fungicide applications were based on weather advisories under SDI (Tables 1 and 2). These data reinforce previous research showing that early leaf spot control using weather advisories to target fungicide applications are as effective as fungicides applied biweekly, and in some instances, the number of fungicide applications can be reduced without sacrificing disease control (Bailey, 1994, 1999; Damicone et al., 1994; Jordan et al., 1999).

Incidence of tomato spotted wilt virus varied by year and irrigation system (Table 3). Incidence was 3% or less in 2001, and there were no differences among irrigation systems or disease management programs (data not presented). In contrast, incidence of tomato spotted wilt virus was much higher in 2002. When pooled over disease management programs, tomato spotted wilt virus incidence was 20% under SDI and 12% under OSI (data not presented). Tomato spotted wilt virus did not differ among disease management programs (p = 0.6204, Table 3). Tomato spotted wilt tospovirus is transmitted by thrips (Frankliniella spp.) generally early in the growing season (Shew, 2003). In our experiment, irrigation and fungicide treatments did not differ until late June after the majority of transmission of virus would have occurred. Additional research is needed to determine the consistency of tomato spotted wilt incidence under various irrigation systems.

When comparing incidence of tomato spotted wilt virus between single- and twin-row planting patterns, 21 and 19% tomato spotted wilt virus occurred in these respective planting patterns under SDI (data not presented). Under OSI, incidence of tomato spotted wilt virus was 13 and 5% with these respective planting patterns (data not presented). While not significantly different in these experiments, incidence of tomato spotted wilt virus in peanut is generally lower when seeding peanut in twin-row planting patterns rather than single-row planting patterns (Brown et al., 1999).

The interaction of year x irrigation system x disease management program was not significant for peanut pod yield (p = 0.9863, Table 3). However, the interaction of year x disease management program was significant (p = 0.0011). In 2001, pod yield was higher when fungicides were applied, regardless of irrigation system or whether or not fungicides were applied biweekly or based on weather advisories (Table 6). In contrast, pod yield was similar in 2002 regardless of disease management program–planting pattern combination. Differences in economic value mirrored those for pod yield (Tables 6). Differences in yield most likely were related to differences in leaf defoliation caused by early leaf spot. The main effect of irrigation system and interactions of year x irrigation system and irrigation system x disease management program were not significant for pod yield or economic value. These data suggest that yield and economic value of peanut grown under SDI and OSI can be similar. Other research (Puppala et al., 2000) has documented similar yields in SDI and OSI systems.

The interaction of year x irrigation system was significant for %ELK (p = 0.0320, Table 3). The main effect of disease management program was also significant (p = 0.0252) for %ELK. However, the main effect of irrigation (p = 0.5366) and the interaction of irrigation system x disease management program (p = 0.3350) were not significant for %ELK. The %ELK was higher under OSI compared with SDI in 2001 (54 vs. 49%, data not presented). However, there was no difference between irrigation systems for this parameter in 2002, with %ELK values of 50% for both irrigation systems (data not presented). Although not substantiated in our experiments, it is suspected that while SDI provided sufficient soil moisture to promote growth of the peanut plant, soil moisture with this irrigation system was limited in the pegging zone. Sorensen et al. (2003) reported difficulty in moving sufficient irrigation water through SDI lines to the pegging zone of peanut. Soil moisture in the pegging zone was more favorable in OSI, and this may have favored greater movement of Ca into the developing pods. Calcium movement into developing pegs and maturing pods is influenced by soil moisture, and lower %ELK values are often associated with suboptimal Ca absorption by these structures (Gascho and Davis, 1995; Jordan et al., 2000). Although not recorded in these experiments, soil temperature may have been cooler in the pegging zone with OSI compared with SDI. Higher temperatures may have been detrimental to pod development and may explain partially why a lower %ELK was noted in SDI compared with OSI in 1 of 2 yr. Sorensen and Wright (2002) suggested that SDI maintained soil temperatures in the pegging zone below a critical value of 29°C (Davidson et al., 1991) from peanut fruit initiation through crop harvest. However, a ceiling for the critical value for soil temperature has not been established for Virginia market type peanut. Additional research is needed to address this issue in SDI.

The %ELK generally increased as disease management intensity increased (Table 7). There was no difference between %ELK for peanut treated biweekly when seeded in single- or twin-row planting patterns. The %ELK was also similar when fungicides were not applied and when they were applied based on weather advisories. More intensive disease management often reduces peanut leaf defoliation and subsequent pod shed. This may explain lower %ELK when fungicides were not applied.

Comparison of Irrigated and Nonirrigated Systems
Although the interaction of year x irrigation system was not significant for peanut pod yield, %FP, %ELK, %SS, or %OK, main effects for some of these parameters were significant (Table 8). Additionally, the interaction of year x irrigation systems was significant for %TSMK (p = 0.0053). When pooled over years, nonirrigated peanut yielded 1020 and 820 kg ha^–1 lower than SDI and OSI systems, respectively (Table 9). However, pod yield under SDI and OSI was similar. Previous research has shown higher yield of irrigated peanut when diseases are controlled. Additional research has shown similar yields when peanut is grown under SDI and OSI systems (Lamb et al., 1997; Puppala et al., 2000).

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Collectively, these data suggest that peanut yield under SDI and OSI systems can be similar. Additionally, when conditions favor development of early leaf spot, incidence may be lower under SDI than OSI, and fewer fungicides applications may be needed to gain acceptable early leaf spot control compared with the number needed under OSI. Although yields were similar under SDI and OSI systems, the %ELK was lower under SDI than under OSI in 1 of 2 yr. Additional research is needed to address market grade characteristics more critically under these irrigation systems. Results from these studies reinforce results from previous research demonstrating that applying fungicides based on weather advisories can be as effective as biweekly fungicide applications.

	ACKNOWLEDGMENTS

 
Appreciation is expressed to the staff at the Peanut Belt Research Station, Sarah Hans, Carl Murphy, Brenda Penny, and Rod Huffman for assistance with these experiments. Appreciation is also expressed to Norris Powell (Tidewater Agricultural Research and Extension Center, VPI and State University) and Marshall Lamb (USDA-ARS National Peanut Research Laboratory) for advice relative to subsurface drip irrigation. Staff at the Tidewater Agricultural Research and Extension Center provided the installation equipment for drip irrigation lines. The North Carolina Peanut Growers Association, Inc., and the North Carolina Agricultural Foundation provided financial support for this research.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Bailey, J.E. 1994. Evolution of a weather-based peanut leaf spot spray advisory in North Carolina. Plant Dis. 78:530–535.
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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Lanier, J. E. Articles by Wells, R. Search for Related Content PubMed Articles by Lanier, J. E. Articles by Wells, R. Agricola Articles by Lanier, J. E. Articles by Wells, R. Related Collections Other Legumes Pest Management Systems Irrigation