Progress 09/01/02 to 02/28/07
Outputs
OUTPUTS: We evaluated the potential of intercropping to reduce early leaf spot (ELS) and late leaf spot (LLS) on peanut over seven seasons in eastern NC. In all trials, four-row strips of peanut were alternated with four rows of another crop in 16-row x 15-m plots, using various Virginia-type cultivars. A randomized complete block design with 4-5 blocks was used each year, employing standard cultivation and weed and insect management practices. The treatments evolved through three phases over time. During 2000-2002, corn was intercropped in low-disease-pressure locations at Castle Hayne or Butner, NC. ELS was reduced 30-73% (p<.05) compared to the monocrop with no reduction in yield. During the 2003-2004 period trials were located in the high-disease location of Lewiston-Woodville, NC and a cotton intercrop added. A reduced-spray schedule, in which two sprays were applied early in the season to delay epidemic onset, also was added. Corn was no longer effective, but cotton reduced ELS
AUDPC by 25-41% in unsprayed plots, and by 60% (p<.05) in combination with a reduced-spray schedule. Intercropping appeared to act by delaying epidemic onset, so in 2005-2006 cultivars or lines with moderate rate-reducing resistance to ELS were introduced to complement this mechanism. Treatments included a monocrop of the susceptible cv Gregory; a monocrop of the partially resistant germplam line GP-NC 343; intercrop of cotton/Gregory or GP-NC 343; intercrop of cotton/Gregory or GP-NC 343 peanut with reduced spray; monocrop of Gregory or GP-NC 343 with reduced spray; and monocrop of Gregory or GP-NC 343 sprayed full season. The predominant disease was late leaf spot (LLS). In contrast to previous years, intercropping did not affect leaf spot incidence or defoliation compared to the corresponding monocrop treatment. We previously have observed that intercropping is more effective against ELS than LLS, which has been the predominant leaf spot since 2004. GP-NC 343 expressed high levels
of resistance to leaf spots and had correspondingly high yields, even in unsprayed monocrop treatments. Peanuts were monitored over two seasons at Lewiston-Woodville to assess microclimatic variations which may mediate disease reductions due to intercropping. Temperature and leaf wetness at canopy height were recorded every 15 minutes in four adjacent rows of peanuts grown in each of three cropping systems: peanut monoculture, peanut/cotton intercrop, or peanut/corn intercrop. The peanut monocrop canopy was warmest (P < .01) and most variable, followed by the corn, then the cotton intercrops, throughout the day and season. Though there was typically no interaction between time of day and treatment (P > 0.10), a diurnal pattern was observed in which differences among treatments were negligible except during the afternoon, when deviations of 2-3 C were common between monocrop and cotton intercrop canopies. Neither daily leaf wetness occurrence nor duration differed among the treatments.
These observations suggest that the suppression of ELS in peanut intercrops largely may be due to the effects of the non-peanut crop on pathogen dispersal rather than microclimatic alterations.
PARTICIPANTS: Individuals: Barbara B. Shew, PI; Mark A. Boudreau, PI; Joyce E. Hollowell, Agricultural Research Specialist, technical assistance; Jennifer Ackland, Undergraduate Student (Imperial College of London, Wye); Mary-Claire Garrison, Undergraduate Student (NCSU), technical assistance; Sarah Amend, Undergraduate Student (NCSU), technical assistance; Eric Olson, Undergraduate Student (NCSU), technical assistance; Jianxia Ma, technical assistance; Cameron Ward, Undergraduate Student (Wake Technical College) technical assistance. Partner Organizations and contacts: NC State University; NC Department of Agriculture; Herbert Green Agroecology; David Jordan, Department of Crop Science; Thomas Isleib, Department of Crop Science. Training and professional development: Jennifer Ackland (M.S. thesis, Imperial College of London, Wye, M. Jeger, chair); Damon Smith, Ph.D. Student (not supported by this project); Sarah Ruark, M.S. Student (not supported by this project)
TARGET AUDIENCES: American Phytopathological Society; American Peanut Education and Research Society; Peanut growers and county agents; Organic producers
PROJECT MODIFICATIONS: Changes were outlined in requests for no cost extensions. Briefly, the project as originally proposed was envisioned as a research program for a graduate student in Plant Pathology. However, we were unable to recruit and secure admission for a graduate student to carry on the research project. Therefore, we relied on existing technical personnel at NCSU (Joyce Hollowell) and numerous undergraduate assistants to complete the project. This meant that the project was completed at a slower pace than outlined in the original proposal. Also unanticipated was the statewide shift in leaf spot from predominantly ELS to LLS, which occurred starting in about 2004. LLS had never predominated in NC prior to this time. The reasons for the shift may include a succession of wetter than normal years in the early 2000's due to hurricane activity (which also is thought to introduce inoculum via long distance transport), widespread deployment of highly susceptible cultivars, and
development of resistance to a commonly used fungicide. Regardless, LLS does not appear to be as amenable to control by intercropping as early leaf spot. The reasons for this difference could not be determined in the current studies.
Impacts
We evaluated the potential of intercropping to reduce early leaf spot (ELS) and late leaf spot (LLS) on peanuts over seven seasons in eastern NC. Intercropping was effective against leaf spots in low disease locations but not in areas with a history of disease, particularly when LLS predominated. The potential for intercropping to reduce peanut leaf spot may be limited to production areas with low background inoculum, or in combination with resistance to ELS and LLS. The high levels of resistance and correspondingly high yields seen in GP-NC 343 indicate that this is a promising line to use in production systems that seek to minimize fungicide use, and in organic production. A major outcome of this project has been the development of approaches that can be used in organic production systems, including use of host resistance, intercropping, and minimal use of approved fungicides timed to optimize disease control.
Publications
- B.B. Shew and M.A. Boudreau. 2007. Intercropping as a tool for disease management in no-spray and reduced spray peanuts. ASA-CSSA-SSSA International Annual Meetings, November 4-8, 2007. III/Div. A08 252-5
- M.A. Boudreau and B.B. Shew. 2006. Microclimatic patterns in peanut intercropped with corn or cotton. Phytopathology 96:S14
- B.B. Shew and M.A. Boudreau. 2005. Development of early leaf spot in peanut intercropped with corn or cotton. Proc. Amer. Peanut Research Educ. Soc. 37:54.
- M. Boudreau and B.B. Shew. 2005. A portable tower for field sampling of diverse vertical profiles. Phytopathology 95:S12.
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Progress 10/01/05 to 09/30/06
Outputs
Leaf spot epidemics were monitored on peanut intercropped with corn or cotton from 2003 to 2006. In 2006, treatments included a monocrop of the susceptible cv Gregory; a monocrop of the partially resistant germplam line GP-NC 343; intercrop of cotton/Gregory or GP-NC 343; intercrop of cotton/Gregory or GP-NC 343 peanut sprayed twice in early season (reduced spray); monocrop of Gregory or GP-NC 343 with reduced spray; and monocrop of Gregory or GP-NC 343 sprayed full season. The line GP-NC 343 has high partial resistance to leaf spots and was included to assess effects of apparent infection rate on the epidemics. The early season sprays were included as a means of assessing effects of disease onset. The predominant foliar disease was late leaf spot. In contrast to previous years, intercropping did not affect leaf spot incidence or defoliation compared to the corresponding monocrop treatment. We previously have observed that intercropping is more effective against early
leaf spot than late leaf spot, which has become the predominant leaf spot in the past two years. GP-NC 343 expressed high levels of resistance to leaf spots and had correspondingly high yields, even in unsprayed treatments. Peanuts were monitored over two seasons at the Peanut Belt Research Station in Lewiston-Woodville, NC to assess microclimatic variations which may mediate disease reductions due to intercropping. Temperature and leaf wetness at canopy height were recorded every 15 minutes in four adjacent rows of peanuts grown in each of three cropping systems: peanut monoculture, peanut/cotton intercrop, or peanut/corn intercrop. The peanut monocrop canopy was warmest (P < .01) and most variable, followed by the corn, then the cotton intercrops, throughout the day and season. Though there was typically no interaction between time of day and treatment (P > 0.10), a diurnal pattern was observed in which differences among treatments were negligible except during the afternoon, when
deviations of 2-3C were common between monocrop and cotton canopies. Neither daily leaf wetness occurrence nor duration differed among the treatments. These observations are consistent with other work which suggests that the suppression of early leaf spot in peanut intercrops largely may be due to the effects of the non-peanut crop on pathogen dispersal rather than microclimatic alterations. Mechanistic studies also were conducted to examine effects of intercropping on spore removal and dispersal. Spore counting for these studies is still underway.
Impacts
The high levels of resistance and correspondingly high yields seen in GP-NC 343 indicate that this is a promising line to use in production systems that seek to minimize fungicide use, and in organic production. Intercropping may be useful in production systems were early leaf spot predominates.
Publications
- M.A. Boudreau and B.B. Shew. 2006. Microclimatic patterns in peanut intercropped with corn or cotton. Phytopathology 96:S14
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Progress 10/01/04 to 09/30/05
Outputs
Leaf spot epidemics were monitored on peanut intercropped with corn or cotton at the Peanut Belt Research Station at Lewiston, NC from 2003 to 2005. The peanut cultivars were NC-V11 in 2003 and Gregory in 2004 and 2005. In all years, plots 16 rows wide by 15 m long were planted in four-row strips of unsprayed peanut/cotton or peanut/corn intercrops, or were planted entirely with peanut monocrops. Treatments included an unsprayed and a sprayed peanut monocrop. In 2004, additional treatments of peanut/cotton and peanut monocrop were sprayed twice early in the season (reduced spray). Leaf wetness and temperature were continuously monitored for each treatment so that microclimate could be compared relative to row location. Early leaf spot was rated on the eight peanut rows of each plot beginning in early August. In 2003 and 2004, AUDPC for early leaf spot was lower in the peanut/cotton intercrop than in the unsprayed peanut monocrop, but higher than in the sprayed peanut
monocrop. Although both years were very favorable for leaf spot development, the reduction in AUDPC relative to the unsprayed control was greater in 2004 than in 2003. In 2005, treatments included a monocrop of the susceptible peanut cultivar Gregory; a monocrop of the partially resistant peanut cultivar Perry; corn/Gregory or Perry intercrop; intercrop of cotton/Gregory or Perry; intercrop of cotton/Gregory with reduced spray; monocrop of Gregory with reduced spray; and monocrop of Gregory sprayed full season. The cultivar Perry has partial resistance to early leaf spot (but not late leaf spot) and was included to assess effects of apparent infection rate on the epidemics. As in 2004, the early season sprays were included as a means of assessing effects of disease onset. Environmental conditions were favorable for disease development and high levels of disease developed in all unsprayed plots. Unlike earlier seasons, however, the predominant foliar disease was late leaf spot. The
early leaf spot resistance in Perry was ineffective against late leaf spot. In 2005, intercropping generally did not affect AUDPCs for late leaf spot compared to the corresponding monocrop treatment (e.g., Perry vs. strip intercrop of cotton and Perry). However, the AUDPC for the strip intercrop of cotton and Gregory sprayed twice in early season was significantly lower than for the corresponding monocrop of Gregory. This pair of treatments also produced the highest yields. Highest levels of disease and lowest yields were found in corn/Gregory intercrop. Comparison of disease progress in the reduced spray intercrop and reduced spray monocrop treatments in 2004 and 2005 suggested that intercropping delayed epidemic onset, but not the rate of disease progress. The results indicate that peanut/cotton intercrops would be of most benefit when epidemic onset is delayed either through use of an early season fungicide spray or in areas of low inoculum, as in fields with long rotations or no
history of peanut production. It also appears that intercropping was less effective in suppressing late leaf spot than suggested by our previous observations of early leaf spot.
Impacts
Strip intercropping may be an alternative means of controlling foliar pathogens in a mechanized agricultural setting. Intercropping may be most effective in organic production systems or other areas where long rotations are used. By developing an understanding of the mechanisms of disease suppression, we will be able to predict if strip intercropping can be applied successfully to other intercrop-disease combinations.
Publications
- Boudreau, M.A. and B. B. Shew. 2005. A portable tower for field sampling of diverse vertical profiles. Phytopatholgy 95:S12.
- Shew, B.B., M.A. Boudreau, and J. Ackland. 2005. Development of Early Leaf Spot in Peanut Intercropped with Corn or Cotton. Proc. Amer. Peanut Res. Educ. Soc. 37: (in press)
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Progress 10/01/03 to 09/30/04
Outputs
Studies to determine whether strip intercropping can be used to manage peanut foliar diseases continued in 2004. The objectives of this work are: to evaluate the efficacy of corn-peanut and cotton-peanut intercropping as a disease management tool for leaf spots; and to continue characterizing the mechanisms of disease suppression in strip intercropping relative to monocrops with the aim of developing deployment strategies for many crops. To address the first objective, 20 plots 15 x 15 m were established at the Peanut Belt Research Station in Lewiston, NC. Each plot consisted of 16 rows and were surrounded on all sides by borders equivalent to 8 rows. The following treatments were replicated six times in a randomized complete block design: a) unsprayed peanut monocrop; b) sprayed peanut monocrop; c) unsprayed strip intercrop representing sets of four alternating peanut and corn rows; and d) unsprayed strip intercrop of four alternating peanut and cotton rows. The
virginia-type cultivar Gregory was used in this experiment. All crops were managed in accordance with recommended practices. In contrast to earlier experiments, these studies relied on the presence of natural inoculum in production areas. An unusually wet summer was highly favorable for disease development. Disease was first observed in scattered foci within plots and final disease incidence was high. Leaf spot assessment continued until peanut digging in early October. Area under the disease progress curve (AUDPC) was less in the cotton strip intercrops than in the other unsprayed treatments. To address the second objective, leaf wetness and temperature were continuously monitored for each treatment (except the sprayed peanut monocrop) in three of the five blocks. Further, because our earlier research suggested the importance of distance to corn on infection, we monitored microclimate factors in each of the four innermost rows of peanuts in these plots. Spore collectors were placed
at two heights in selected plots to determine effects of intercropping on spore movement within plots.
Impacts
Strip intercropping may be an alternative means of controlling foliar pathogens in a mechanized agricultural setting. By developing an understanding of the mechanisms of disease suppression, we will be able to predict if strip intercropping can be applied successfully to other intercrop-disease combinations.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Studies to determine whether strip intercropping can be used to manage peanut foliar diseases began in 2003. The objectives of this work are: to evaluate the efficacy of corn-peanut and cotton-peanut intercropping as a disease management tool for leaf spots; and to continue characterizing the mechanisms of disease suppression in strip intercropping relative to monocrops with the aim of developing deployment strategies for many crops. To address the first objective, 20 plots 15 x 15 m were established at the Peanut Belt Research Station in Lewiston, NC. Each plot consisted of 16 rows and were surrounded on all sides by borders equivalent to 8 rows. The following treatments were replicated six times in a randomized complete block design: a) unsprayed peanut monocrop; b) sprayed peanut monocrop; c) unsprayed strip intercrop representing sets of four alternating peanut and corn rows; and d) unsprayed strip intercrop of four alternating peanut and cotton rows. The
virginia-type cultivar NC-V 11 was used in this experiment. All crops were managed in accordance with recommended practices. In contrast to earlier experiments, these studies relied on the presence of natural inoculum in production areas. An unusually wet and cool summer was highly favorable for disease development. Disease was first observed in scattered foci within plots and final disease incidence was high. Leaf spot assessment continued until peanut digging in early October. Area under the disease progress curve (AUDPC) was less in the cotton strip intercrops than in the other unsprayed treatments. To address the second objective, leaf wetness and temperature were continuously monitored for each treatment (except the sprayed peanut monocrop) in three of the five blocks. Further, because our earlier research suggested the importance of distance to corn on infection, we monitored microclimate factors in each of the four innermost rows of peanuts in these plots. Spore collectors were
placed at two heights in selected plots to determine effects of intercropping on spore movement within plots. We have continued to conduct analysis of data collected during the initial phase of this project. Those analyses further support our preliminary conclusions that interference with dispersal phenomena is the primary means by which strip intercropping inhibits development of early leaf spot in peanut.
Impacts
Strip intercropping may be an alternative means of controlling foliar pathogens in a mechanized agricultural setting. By developing an understanding of the mechanisms of disease suppression, we will be able to predict if strip intercropping can be applied successfully to other intercrop-disease combinations.
Publications
- M.A. Boudreau, B.B. Shew, and L.E. Duffie. 2003. Mechanisms of peanut early leaf spot reductions in maize intercrops. Phytopathology 93:S10.
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Progress 09/01/02 to 12/31/02
Outputs
We have conducted extensive analysis of data collected during the initial phase of this project. Those analyses further support our preliminary conclusions that interference with dispersal phenomena is the primary means by which strip intercropping with corn inhibits development of early leaf spot in peanut. Field research on the current project will begin in the summer of 2003. In preparation for the 2003 growing season, we began efforts to recruit candidates for the graduate research assistantship provided in this project. Other preliminary tasks which have been initiated include identifying land for planting field plots, locating cultures of Cercospora nicotiane and seed of appropriate tobacco cultivars, and identifying sources of needed environmental monitoring equipment.
Impacts
Strip intercropping may be an alternative means of controlling foliar pathogens in a mechanized agricultural setting. Our research indicates suppression of early leaf spot disease when peanut is grown in strip intercrops with corn. By developing an understanding of the mechanisms of disease suppression, we will be able to predict if strip intercropping can be applied successfully to other intercrop-disease combinations.
Publications
- No publications reported this period
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