Browsing by Author "Turner Sutton, Committee Co-Chair"

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    Potential for Management of Sclerotinia Blight of Peanut (Arachis hypogaea L.) caused by Sclerotinia minor with the Biological Control Agent Coniothyrium minitans
    (2006-04-05) Partridge, Darcy Erin; Marc Cubeta, Committee Member; Barbara Shew, Committee Member; Turner Sutton, Committee Co-Chair; David Jordan, Committee Co-Chair
    Sclerotinia blight of peanut (Arachis hypogaea L.), caused by Sclerotinia minor (Jagger) Kohn, is an important disease in North Carolina and Virginia. Sclerotia are the main overwintering propagules of S. minor and serve as the primary source of inoculum for Sclerotinia blight. The effectiveness of the fungal mycoparasite Coniothyrium minitans, which is capable of colonizing sclerotia of Sclerotinia spp., was evaluated in a 5-year field study and in eight short-term field studies in northeastern North Carolina. Control of Sclerotinia blight was highest when C. minitans was applied for 3 consecutive years. However, application of C. minitans for 1 or 2 years also reduced disease in the long-term study. A single application of C. minitans was less effective when applied 4 to 6 months prior to planting and sclerotia numbers were only reduced in two of the eight short-term field studies. Sclerotia used as baits placed in the long-term field study as well as the sclerotia isolated from soil were infected by C. minitans, and the number of sclerotia was reduced where C. minitans was applied. Moderate resistance in the cultivar Perry and application of the fungicide fluazinam provided adequate control of Sclerotinia blight in all plots. The integration of C. minitans with current peanut management practices is needed for successful biological control of Sclerotinia blight. Laboratory experiments evaluated the effects of nine pesticides commonly used in peanut production on mycelial growth, conidia germination, and mycoparasitic activity of C. minitans on sclerotia of S. minor. The commercial formulations of the fungicides azoxystrobin, chlorothalonil, fluazinam, pyraclostrobin, and tebuconazole, and the herbicide flumioxazin reduced mycelial growth and conidia germination of C. minitans. Eight of nine pesticides, azoxystrobin, chlorothalonil, fluazinam, pyraclostrobin, tebuconazole, diclosulam, flumioxazin, and pendimethalin applied to soil plates reduced but did not inhibit the mycoparasitic activity of C. minitans on sclerotia of S. minor. Temperature and moisture effects on mycoparasitism were also evaluated to determine optimum conditions for infection of sclerotia of S. minor by C. minitans. Optimum temperatures for infection of sclerotia of S. minor by C. minitans ranged from 14 to 22°C and soil moisture –0.33 to –1 kPa x 10². These results indicate that C. minitans should remain active throughout most of the year in North Carolina, except during the hot summer months of June, July and August. Soil fauna such as collembola may aid in the reduction of sclerotia through direct predation and the movement of inocula of mycoparasites from infected to noninfected sclerotia. Collembola diversity and abundance were compared in four peanut fields. The most prevalent collembola families were Isotomidae, Smithurididae, Poduridae, and Hypogastruridae, with Isotomidae isolated most frequently from all sites. Abundance and diversity of collembola increased from August to October with sampling date and location having the greatest effect on the composition of the population. Determining the abundance and diversity of collembola in the field can help increase our understanding of the soil community structure. These studies show that C. minitans is able to persist and infect sclerotia of S. minor in peanut fields of North Carolina when applied in the fall or early winter across crop residue and incorporated into the top layers of the soil. C. minitans will not eradicate infestations by S. minor, but over time has the potential to reduce inoculum levels and ultimately decrease the incidence of the disease.
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    Potential Use of Hyperspectral and Multispectral Remote Sensing Imagery to Enhance Management of Peanut (Arachis hypogaea L.)
    (2006-11-08) Seth Carley, Danesha; Michael Burton, Committee Member; Turner Sutton, Committee Co-Chair; Cecil Dharmasri, Committee Member; Rick Brandenburg, Committee Member; David L. Jordan, Committee Co-Chair
    Experiments were conducted during 2003 and 2004 to determine if peanut yield and market quality factors differed when paraquat was applied 24 to 28 days after emergence or when 2,4-DB was applied in mid August when peanut was seeded during the early, mid-, and late May and during early June. In other experiments conducted from 2003-2004, peanut was planted with or without aldicarb in the seed furrow to control tobacco thrips (Frankliniella fusca Hinds). In a final set of experiments conducted during 2005, treatments consisted of seeding with or without aldicarb followed by no paraquat or paraquat applied 24 to 28 days after emergence. Peanut yield and percentages of extra large kernels, total sound mature kernels, and farmer stock fancy pods were affected by planting date and pesticide treatment independently. Pod yield was higher in one of two years when peanut was planted in early and mid May compared with late May and June planting. In the other year peanut yield was higher when seeded in mid-May compared to early or late May or early June. In three of nine experiments failure to control tobacco thrips by not applying aldciarb reduced pod yield. In five experiments pod mesocarp color was used to determine if damage form tobacco thrips or paraquat delayed pod development and maturation. No differences in percentages of pods considered ready for digging were noted even though significant tobacco thrips damage and injury from paraquat was observed early in the season. A number of differences in canopy reflectance were noted when hyperspectral imaging was used within 1 wk of digging and inverting vines but were not associated with pod maturation. Further research was conducted in North Carolina from 2003-2005 to determine if reflectance of the peanut canopy could be used as an indicator of pod maturation. The cultivars VA 98R and NC-V 11 were planted beginning in early May through early June during each year and reflectance was measured in mid- to late September and was compared with the percentage of pods in the brown and black mesocarp color. The cultivars Gregory and NC 12C were dug weekly beginning in mid September through mid October. Reflectance was determined at two dates spaced approximately 2 weeks apart for the cultivar Gregory. Experiments were also conducted to determine differences in reflectance of the cultivars Gregory and Georgia Green and to determine if reflectance differed when comparing the cultivars VA 98R and Perry seeded in single and twin row planting patterns. Pod yield was affected by planting date with optimum yield occurring when peanut was planted in mid-May. Although pod yield differed among experiments, percentages of extra large kernels (%ELK) and total sound mature kernels (%TSMK) increased as digging was delayed. Pod yield of the cultivars Georgia Green and Gregory was similar in 4 of 6 experiments; yield of Georgia Green exceeded that of Gregory in two experiments. Planting peanut in twin rows resulted in higher yields than planting in single rows regardless of year or cultivar. Reflectance differed in only 1 of 3 years for the cultivar VA 98R and in no years for the cultivar NC-V 11 even though the percentage of mature pods ranged from 15 to 69% when assessed in mid- to late September. Differences in reflectance were noted when comparing the cultivars Gregory and Georgia Green but not the cultivars VA 98R and Perry. Reflectance did not differ when comparing row patterns. Research was conducted during 2004 and 2005 to develop spectral signatures of peanut with visual symptoms of nitrogen (N) deficiency, injury from a combination of low pH and Zinc (Zn) toxicity, drought stress, early leaf spot (Cercospora arachidicola Hori) and web blotch (Phoma arachidicola Marasas et al.) lesions, and following application of acifluorfen, bentazon, clethodim, imazapic, paraquat, and 2,4-DB. Each of the studies showed some differences in spectral reflectance. However, it was difficult to distinguish the herbicide treated plants from the nutrient- and drought-stressed plants due to the similarities in spectral characteristics. Research was conducted in North Carolina during 2003, 2004, and 2005 to determine the relationship between canopy defoliation and peanut yield. Applying fungicides bi-weekly beginning in early July through mid September resulted in less canopy defoliation than applying only two sprays in July or not applying fungicide and in many instances increased pod yield. When peanut canopy defoliation exceeded approximately 50%, digging 6 to 12 days prior to projected optimum maturity resulted in higher yields than digging at optimum maturity. However, response to early digging was variable when defoliation at the early digging date was less than approximately 50%.