Twelve field trials were completed in North Carolina from 2005 to 2007 to determine the impact of planting pattern on peanut yield, market grade characteristics, and pest reaction for the Virginia market type cultivars Perry and VA 98R. The first set of experiments was designed to evaluate incidence of Cylindrocladium black rot (caused by
Efficient management of pests is important in optimizing peanut yield and economic returns (
Southern corn rootworm (SCRW) is a primary pest of peanut in fine-textured soils, and direct injury is caused by larvae penetrating the pod to feed on the kernel. Pod scarring occurs when larvae are unsuccessful at penetrating the outer pod wall, and can reduce peanut value. Because larvae are subterranean, scouting is difficult; therefore, SCRW control with insecticides is preventive. The decision to make an insecticide application is based upon a risk index calculation of conditions particular to the site (
Disease management in peanut is important to optimize both yield and quality. Uncontrolled diseases result in yield losses of up to 50% (
Cylindrocladium black rot (CBR), which is caused by the soil-borne fungus
Peanut is also susceptible to several plant parasitic nematodes, including northern root knot (
Various factors specific to the cropping system must be considered, and weighed by the grower in order to make the most prudent pest management decisions with regard to the environment and the profitability of the farm enterprise. Cultivar selection is important because different cultivars express considerable differences in resistance to individual diseases, especially to TSW, CBR, and SB (
While the role of twin row planting patterns is well documented in reducing incidence of TSW in peanut, comprehensive research has not been conducted in North Carolina to determine the broader impact of twin row plantings on other pests. Therefore, the objective of this research was to determine how peanut disease management practices interact with planting pattern to affect disease incidence, yield, and market grade characteristics in Virginia market type cultivars.
Six experiments were completed in North Carolina during 2005, 2006, and 2007; two in farmer-owned fields in 2005 (Bethel) and (Chadbourn), three at the Peanut Belt Research Station located in Lewiston-Woodville in 2006 (Fields A2, B3, and C2) and in one field during 2007 (Field F3). One of the most important management considerations for CBR is the disease history of the field, and each of these locations and fields had a history of CBR. Soil at the Bethel site was an Exum fine sandy loam (fine-silty, siliceous, thermic Typic Paleudult). Soil at the Chadbourn site was a Norfolk loamy fine sand (fine-loamy, siliceous, thermic typic Paleudult). Soil at the Peanut Belt Research Station was a Norfolk loamy sand (fine-loamy, kaolinitic, thermic typic Kandiudults). Plot size was four rows wide (91-cm spacing) and 12.2 m long in Bethel and Chadbourn and 9.1 m long at Lewiston-Woodville.
Treatments included a factorial arrangement of two cultivars (Perry and VA 98R), two levels of fumigation (none or metam sodium at 112 L/ha), and two planting patterns (single or twin rows). The twin row planting pattern consisted of two rows spaced 20 cm apart on 91-cm spacing. Final in-row plant populations ranged from 11 to 14 plants/m and 15-17 plants/m in single and twin row planting patterns, respectively. Metam sodium (Vapam HL, Amvac Chemical Corp., Los Angeles, CA) was delivered 25 cm below projected seed placement in raised seedbeds 2 weeks prior to planting. Aldicarb (Temik 15G, Bayer CropScience, Research Triangle Park, NC) at 1.1 kg ai/ha and
Four experiments were completed in North Carolina during 2005, 2006 and 2007; two at farmer-owned fields in 2005 (Corapeak) and 2006 (Roxobel), and one at the Peanut Belt Research Station in Lewiston-Woodville in each of 2006 (Field B3) and 2007 (Field F3). Fields were selected because they had a history of SB in peanut based on the growers’ experience. Soil at the Corapeak site was a Goldsboro fine sandy loam (fine-loamy, siliceous, subactive, thermic Aquic Paleudults). Soil at the Roxobel site was a Norfolk sandy loam (fine-loamy, siliceous, thermic Typic Kandiudults). Soil at the Peanut Belt Research Station was a Norfolk loamy sand (fine-loamy, kaolinitic, thermic typic Kandiudults). Plot size was four rows wide (91-cm spacing) and 12.2 m long at Corapeak, four rows wide (93-cm spacing) and 7.6 m long at Roxobel, and four rows wide (91-cm spacing) and 9.1 m long at Lewiston-Woodville.
Treatments included a factorial arrangement of two cultivars (Perry and VA 98R), two levels of boscalid (Endura fungicide, BASF Corp., Research Triangle Park, NC) (none or boscalid at 0.44 kg/ha), and two planting patterns (single or twin rows). Aldicarb at 1.1 kg/ha and
Weeds were controlled with the same preplant incorporated, preemergence, and postemergence herbicides for all treatments at a given location or year and location combination, but differed across years and locations. Chlorpyrifos (Lorsban 15G, Dow Agroscience, Indianapolis, IN) was applied based upon calculations made for each location using the SCRW index (
Foliar damage from tobacco thrips feeding was recorded in 2006 approximately 3 weeks after planting by evaluating 10 of the most recently emerged leaflets for feeding damage using a scale of 1 to 3, where 0 = no foliage damaged and 3 = all foliage damaged. Incidence of CBR was evaluated by counting dead and severely wilted plants in the center two rows of each plot in late September. Plants exhibiting wilting and yellowing were not counted if symptoms of spotted wilt were apparent, whereas wilted plants that yielded to a firm tug on the main stem were assumed to have root and crown rot caused by CBR. Incidence of SB was determined in late September by parting the canopy in the center two rows of each plot and inspecting stems and crowns for symptoms of the disease. Symptomatic plants were marked with surveyor's flags, and all flags were counted when ratings were completed. Leaf spots (both early and late) were evaluated on a 1.2 m section of row in the center two rows of each plot. The section to be rated was determined prior to rating by computer randomization. A rating of plant condition, which is an overall measure of cumulative defoliation and disease, was recorded within 2 weeks prior to digging using a scale of 0 = no disease and 100 = entire canopy expressing disease symptoms.
Soil samples were taken from each plot during the first week of June (2005 and 2006) to determine populations of plant parasitic nematodes. Approximately 20 soil cores (10 cm diameter by approximately 12 cm deep) were collected from each plot in a zigzag pattern and combined into one sample per plot. To determine populations of microsclerotia of
Optimum maturity was determined for each cultivar using the pod mesocarp color technique (
The experimental design was a split-plot with cultivars (Perry and VA 98R) serving as the whole plot unit. Depending on the experiment, combinations of either fumigation for CBR suppression or application of boscalid for Sclerotinia blight suppression were combined with planting patterns (single and twin rows) to create sub plots. Treatments were replicated four times. Data for CBR,
Significant differences were found for inoculum density of
Nematode populations were relatively low in all trials. For ring nematode, a trial by planting pattern by fumigation interaction was significant (p = 0.0215), and this interaction most likely was caused by fewer nematodes being present in single rows following fumigation compared with no effect of fumigation in twin rows (
Influence of trial and fumigation on lesion nematode population; trial, planting pattern and fumigation on ring nematode; and trial and cultivar on root knot nematode when sampled in the experiment designed to manage Cylindrocladium black rot.a
The interaction of trial by fumigation was significant for lesion nematodes (p = 0.0145), where fumigation reduced soil populations in the Chadbourn trial but in none of the other trials (
Planting pattern did not affect TSW or interact with other treatments (p
The interaction of cultivar by planting pattern was significant (p = 0.0093) for tobacco thrips injury observed 2 weeks after peanut emergence. Interactions of trial (combination of year and location) by all other treatment factors were not significant for thrips injury (p
Interactions of trial by planting pattern (p = 0.0213) and trial by cultivar (p = 0.0009) were significant for pod scarring caused by SCRW. When pooled over fumigation treatments and cultivars, greater damage from SCRW was noted in twin rows at Chadbourn than in single rows even though chlorpyrifos was applied (
Influence of planting pattern and cultivar on pod scarring at harvest in each trial of the experiment designed to manage Cylindrocladium black rot.a
Interactions of trial by cultivar (p = 0.0099) and trial by planting pattern (p = 0.0020) were significant for pod yield. A difference in yield was noted in each trial when comparing cultivars but the differences were not consistent (
Influence of cultivar and planting pattern on pod yield of peanut in the experiment designed to manage Cylindrocladium black rot.a
In 4 of 6 trials, planting peanut in twin rows increased yield by 330 to 550 kg/ha over single rows regardless of cultivar (
In one trial each for Perry and VA 98R, %ELK was highest when planted in twin rows, while in another trial %ELK was highest for VA 98R planted in single rows (
Influence of cultivar and planting pattern on the percentage of extra-large kernels in the experiment designed to manage Cylindrocladium black rot.a
Planting pattern did not affect SB incidence (p = 0.4031). However, higher seeding rates in twin rows would be expected to increase SB given that the risk of SB increases as the canopy closes (
Collectively, results from these experiments reveal the complexity of selecting IPM strategies in peanut when multiple pests are present across diverse environments and fields. Although interactions among treatment factors were noted, oftentimes responses were independent or interactions could be explained by differences in disease potential among the treatments or locations. However, when making management decisions, it is highly problematic that disease histories frequently are unreliable, as seen in these studies. All fields were selected based on previous history of disease but no disease developed in two of six CBR trials and two of four SB trials. The mistaken CBR history at Chadbourn likely resulted from an earlier misdiagnosed epidemic of TSW but the lack of disease in other trials is harder to explain. Obtaining reliable histories of SB is particularly difficult due to the strong influence of environment and within-field clustering of inoculum in this pathosystem (
Research associated with pest management in peanut often focuses on interactions of a specific intervention such as insecticide or fungicide with cultivars or cultural practices such as seeding rates, planting dates, or digging dates with cultivars. The most recent in-depth study in North Carolina with more than two pest management components was conducted in 1997 and 1998 comparing preventative and threshold-based approaches for Virginia market type peanut (
Results from this research suggest that pest reaction to twin-row planting pattern in North Carolina with the Virginia market type peanut often will be the same as pest reaction in the traditional single row planting pattern. Yield increases were common for peanut in twin rows compared with single rows irrespective of pest management input. A limitation to results from these and similar large scale experiments is the relatively rapid adoptation of new cultivars and pest management products. For example, the cultivars Perry and VA 98R have been replaced by more recently released cultivars and are no longer grown in North Carolina. However, results from these experiments illustrate the importance of continuing to formulate comprehensive pest management strategies and validating them experimentally as production practices change.
Gratitude is expressed to the farmers who provide land for this research; they include Joey Baker (Roxobell site); G. P. Kittrell, (Corapeak site), the Hayes Farm (Edenton site), B. Lennon (Chadbourn site), and K. Mann (Bethel site). We also thank Richard Rhodes, Michael Shaw, Sam Uzzell, and Michael Williams for their assistance as Cooperative Extension agents with the on-farm trials. The authors also thank Dewayne Johnson, Brenda Watson, Joyce Hollowell, and Brian Royals for their technical help and assistance in collecting data. This research was supported by funds obtained from a USDACAR (Crops at Risk) grant and USAID Peanut CRSP project LAG-G-00-96-90013-00.