Southern Stem Rot Research Articles

Management Efficacy and Response to Post-Application Precipitation of Fungicides for Southern Stem Rot of Peanut and Evaluation of Co-Application with Micronized Sulfur

Southern stem rot (SSR) is caused by Athelia rolfsii and is an economically important disease of peanut (Arachis hypogaea L.). Application of protectant fungicides is an effective management component for reducing levels of this soil-borne disease. The majority of peanut hectarage in South Carolina and Mississippi is rainfed. Timely precipitation has the potential to aid the movement of foliar-applied fungicides through the canopy and into contact with soil interfaces where SSR infections occur. Questions have arisen as to the quantitative relationship of post-application precipitation and fungicide-active ingredient efficacy in managing SSR and protecting associated pod yield potentials. To examine this, fungicide efficacy experiments were screened for inclusion in a meta-analysis, from which eleven experiments conducted from 2015 to 2023 were selected and paired with environmental data from nearby weather stations. Precipitation during the two days following fungicide application was associated with significant reduction in SSR incidence (logit rate of −0.0039/mm) and increased pod yield (log slope of 0.0028/mm). Active ingredient interactions with precipitation among pod yield but not SSR incidence data were present for benzovindiflupyr plus azoxystrobin, flutolanil, and tebuconazole. Fungicides with the greatest levels of control per application at maximum label rates were inpyrfluxam (18.8%), benzovindiflupyr plus azoxystrobin (15.4%), flutolanil (12.3%), and prothioconazole plus tebuconazole (10.5%). Micronized sulfur neither contributed to SSR control nor pod yield increase. Tebuconazole was associated with the greatest % SSR control per fungicide product cost (0.47%/$/ha/application) but was also the treatment with the least amount of control (3.5%) at its maximum label rate. Maximum label rates of benzovindiflupyr plus azoxystrobin (USD 637) and inpyrfluxam (USD 548) were estimated as conferring the greatest returns over the chlorothalonil-only control. Results serve as a helpful reference for farmers and practitioners in selecting fungicide management options and targeting application times, as feasible, to utilize natural precipitation to improve management outcomes.

Comparison of Current Peanut Fungicides Against Athelia rolfsii Through a Laboratory Bioassay of Detached Plant Tissues.

Southern stem rot of peanut, caused by Athelia rolfsii, is an important fungal disease that impacts peanut production worldwide. Foliar-applied fungicides are used to manage the disease, and several fungicides have been recently registered for southern stem rot control in peanuts. This study compared fungicidal, residual, and potential systemic activity of current fungicides against A. rolfsii using a laboratory bioassay. Peanut plants grown in the field were treated with eight fungicides approximately 90 days after planting, and plants were collected for the laboratory bioassay weekly for 5 weeks following application. Peanut plants were separated into the newest fully mature leaf present at sample collection, the second newest fully mature leaf present at the time of fungicide application, the upper stem, and the crown tissues. Each plant tissue was inoculated with A. rolfsii then incubated at 30°C for 2 days. Lesion length was measured, and percent inhibition of fungal growth by each fungicide relative to the control was calculated. All fungicides provided the greatest inhibition of A. rolfsii on leaf tissues that were present at the time of fungicide application, followed by the newly grown leaf and upper stem. Little inhibition occurred on the crown. Fungal inhibition decreased at similar rates over time for all fungicides tested. Succinate dehydrogenase inhibitors provided less basipetal protection of upper stems than quinone outside inhibitor or demethylation inhibitor fungicides. Properties of the fungicides characterized in this study, including several newly registered products, are useful for developing fungicide application recommendations to maximize their efficacy in controlling both foliar and soilborne peanut diseases.

Late Leaf Spot Defoliation, Microclimate Modification, and Southern Stem Rot Development in Peanut (Arachis hypogaea L.) in South Carolina

ABSTRACT Southern stem rot (SSR) of peanut, caused by Athelia rolfsii, is commonly influenced by environmental conditions. Defoliation from late leaf spot (LLS), caused by Nothopassalora personata, alters canopy structure and has the potential to affect microclimates. A better understanding of the potential interaction between SSR and LLS through potential microclimate modification might contribute to improved disease management. Eight field experiments were conducted from 2016 to 2019 to investigate the effect of LLS defoliation on peanut canopy and soil microclimates and SSR development. To encourage different levels of LLS defoliation, 3 spray programs (3, 4 and 6 chlorothalonil applications) were applied across four cultivars varying in susceptibility to LLS and SSR via a split-plot design. Defoliation was rated every 2 weeks from 75 days after planting (DAP) to harvest. Canopy and soil temperature and soil moisture were recorded from 75 to 140 DAP. Interaction of LLS spray program and peanut cultivar significantly affected LLS defoliation in nearly all trial years except in 2019 where low disease pressure occurred due to dry weather. Significant relationships were observed between LLS defoliation and daily maximum canopy temperatures and between area under LLS defoliation curve (AUDC) and slope of daily canopy temperature change. The influence of LLS defoliation on the microclimate was generally erratic. The relationship between AUDC and SSR was not significant. Results from this study suggest that the influence of LLS on microclimate was insufficient to substantially affect SSR development.

Spectral and Thermal Responses of Peanut to Infection and Colonization with Athelia rolfsii

Soilborne fungal diseases, including southern stem rot (causal agent: Athelia rolfsii), are major constraints to peanut production worldwide. Scouting for disease via visual observation is time and labor intensive but sensor technologies are a promising tool for plant disease detection. Prior research has focused on foliar diseases, and few studies have applied sensor-based tools for early detection of soilborne diseases. This study characterized the temporal progress of spectral and thermal responses of peanut plants during infection and colonization with A. rolfsii under controlled environment. In greenhouse experiments, A. rolfsii-inoculated and mock-inoculated lateral stems of peanut were inspected daily for symptoms, and leaf spectral reflectance and temperature were measured using a handheld spectrometer and thermal camera, respectively. Following onset of visual disease symptoms, leaflets on inoculated stems had greater spectral reflectance in the visible region compared with those on mock-inoculated stems. Leaflets on the inoculated stems also had greater normalized leaf temperatures as compared with leaflets on mock-inoculated stems. Overall, results indicate that signatures of disease development can be detected during peanut infection and colonization with A. rolfsii using spectral reflectance and thermal imaging technologies, and spectral signatures of disease are more consistent and specific compared with thermal ones. Though only one peanut variety, one pathogen isolate, and one single measurement were assessed per evaluation date, temporal progress of spectral and thermal responses on a daily basis characterized in this study can be used to develop sensor-based methods to detect southern stem rot and other soilborne diseases ultimately in the field. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Phenotypic identification of peanut germplasm for resistance to southern stem rot

Southern stem rot, caused by Sclerotium rolfsii Sacc., is a destructive soil fungal disease of peanut in China and other countries. To evaluate resistant germplasm, a total of 256 peanut accessions were investigated on their resistance to southern stem rot in 3 environments by artificial inoculation. Variance analysis indicated that disease index was significantly influenced by environment, genotype and genotype ​× ​environment interactions. Peanut accessions of var. vulgaris type exhibited higher resistance to southern stem rot. Disease index was significantly negatively correlated with linoleic acid content, while positively correlated with oleic acid content. Six resistant accessions were identified, including Hua 28, Shandongzai, ICG 6326, Quanhua 7, Quanhua 9 and Guihua 836, with their disease indexes under 40 and mortality were less than 30% in the three environments. The identified resistant accessions showed the great potential to be applied in resistant peanut breeding, and would be good genetic resources for enhancing the resistance to southern stem rot.

Novel endophytic fungi with fungicidal metabolites suppress sclerotium disease

This study is aimed to investigate the antifungal activity of endophytic fungi isolated from Jerusalem artichoke (Helianthus tuberosus) and Ginger (Zingiber officinale) and Stemona root (Stemona tuberosa) against causative agent of southern stem rot Sclerotium rolfsii. The dual assay results showed that out of 110 fungal endophytes, Diaporthe phaseolorum BUP3/1 and Macrophomina phaseolina BUP2/3, isolated from Jerusalem artichoke and Daldinia eschscholtzii 2NTYL11 and Trichoderma erinaceum ST-KKU2, isolated from Stemona root and ginger could effectively inhibited the mycelial growth of S. rolfsii at 76.00, 41.20, 66.67 and 63.63%, respectively. The β-1,3 glucanase and chitinase activities of all endophytic fungi was determined which reached the maximum after 2 and 7 days of incubation, respectively. In addition, Scanning Electron Microscope (SEM) observation showed that T. erinaceum ST-KKU2 has predatory mechanism aginst S. rolfsii via coiling and invasion. Interestingly, our endophytic fungi T. erinaceum ST-KKU2 and D. eschscholtzii 2NTYL11 were the first species in their genera to produce polyketides group as 6-n-pentyl-2H-pyran-2-one (6PAP) and 2,3-dihydro-5-hydroxy-2-methyl-4H-1-benzopyran-4-one (DHMB), respectively, to control S. rolfsii. Moreover, the antagonistic mechanisms of all endophytes were determined in vivo under greenhouse condition. The endophytic fungi, T. erinaceum ST-KKU2 and D. eschscholtzii 2NTYL11 also showed high level of reduction of southern stem rot disease by 58.14% under pot experiment. Such effects were also higher than the effects of other endophytic fungi isolated from Jerusalem artichoke when tested under greenhouse condition. Our experiments showed the fungal endophytes isolated have potential for further development as a biocontrol agent in the future.

Quantitative trait loci sequencing–derived molecular markers for selection of stem rot resistance in peanut

AbstractDeveloping markers linked to key traits has been a focus of peanut (Arachis hypogaea L.) genomics in the postgenome era. Multiple disease resistance traits have been found to be qualitative and controlled by major quantitative trait loci (QTL) or even single genes while others are more complex. Southern stem rot (stem rot in short) is a devastating disease of peanut caused by the fungus Sclerotium rolfsii. It has been one of the most damaging diseases of peanut with regard to both cost of control and yield loss in the southeastern United States for the last decade. The disease is initiated annually from sclerotia in the soil. The nonuniform distribution of these propagules leads to the nonuniform development of disease, which makes phenotyping and genetic mapping of resistance difficult. Here we report the mapping of two QTL regions controlling stem rot resistance in peanut. Using careful field evaluation, resistant and susceptible bulks were identified from a recombinant inbred line (RIL) population and subjected to QTL sequencing (QTL‐seq). Developed SNP markers linked to the QTL were validated in a blind selection test by selecting only with markers in a part of the population not used for initial analysis. The lines selected for bulk sequencing also were shown to have strong separation for resistance in an independent field experiment. This work not only delivers markers for marker‐assisted selection (MAS) for an important disease in peanut but shows that QTL‐seq can work effectively even when considering highly complex, and quantitative traits.

Resistance to Athelia rolfsii and Web Blotch in the U.S. Mini-core Collection

ABSTRACT Athelia rolfsii (=Sclerotium rolfsii) is a soilborne fungus that causes the disease commonly known as southern blight, southern stem rot, stem rot, and white mold. Despite the fact that A. rolfsii is one of the most destructive pathogens of peanut, the U.S. germplasm collection has not been evaluated for resistance to this pathogen. Therefore, 71 of the 112 accessions comprising the U.S. peanut mini-core collection were evaluated in the field for resistance to southern blight in 2016 to 2018 in Oklahoma. Moderate to low levels of southern blight were observed, but four accessions—CC125, CC208, CC559, and CC650—had low levels of disease in 2017 and 2018, the most favourable years for A. rolfsii. Ratings for web blotch, a yield-limiting foliar disease in some production areas caused by Didymella arachidicola, were also taken in 2017 and 2018, when outbreaks occurred. Five entries—CC287, CC155, CC149, CC812, and CC559—had between 10% and 20% disease in 2018, a year when over half of the mini-core accessions exhibited between 50% and 93% disease. Because cultivated peanut in the U.S. has a narrow genetic base, these results will be useful to breeders seeking additional sources of resistance to A. rolfsii and web blotch.

2016 Evaluation of Foliar Fungicides for Disease Control in Peanut, Jay, FL

This report includes a summary of the 2016 foliar fungicide programs for control of early and late leaf spot and white mold (southern stem rot) in peanut at Jay, Florida. It shows the effectiveness of 13 fungicide programs for disease control. All programs contained active ingredients for the control of white mold (Sclerotium rolfsii) except the Bravo treatment (program #2), which was considered a control. These data represent only one year at one location, and readers are cautioned that test results should be considered over several locations and years before final conclusions are considered valid. These data are meant to serve as a guide in the selection of effective fungicide programs for peanut.

Comparative susceptibility of peanut genetically engineered for sclerotinia blight resistance to non-target peanut pathogens

Field trials were conducted from 2006 to 2008 at the Tidewater Agricultural Research and Extension Center (TAREC) in Suffolk, Virginia to determine whether Blight Blocker transgenic peanut lines showed possible increased or decreased susceptibility to common peanut pathogens. Disease susceptibility was evaluated for seven transgenic lines containing a barley oxalate oxidase gene and their corresponding parental cultivars (Perry, Wilson, NC 7). In addition to Sclerotinia blight, the peanut diseases evaluated included: i) early leaf spot caused by Cercospora arachidicola, ii) Cylindrocladium black rot caused by Cylindrocladium parasiticum, iii) southern stem rot caused by Sclerotium rolfsii, iv) tomato spotted wilt virus, and v) aflatoxin levels in seeds caused by Aspergillus flavus or A. parasiticus. Results demonstrated that the susceptibility of Blight Blocker transgenic lines to common peanut pathogens was similar to that of non-transgenic cultivars, while transgenic lines provided resistance to Sclerotinia blight caused by S. minor. Transgenic lines consistently provided high levels of resistance to S. minor in all three years, however, the barley oxalate oxidase had little or no effect on the disease susceptibility to other organisms on peanut. The results of this research should provide additional evidence needed to petition for deregulation of Blight Blocker peanut lines.

2013 Evaluation of In-Furrow and Foliar Fungicides for Disease Control in Peanut in Jay, Florida

This 10-page fact sheet summarizes the 2013 in-furrow and foliar fungicide programs for control of early and late leaf spot and white mold (southern stem rot) of peanut in Jay, Florida. It shows the effectiveness of 13 fungicide programs for disease control, as compared to no treatment. This data represents only one year and one location, and readers are cautioned that test results should be considered over several locations and years before final conclusions are valid. Written by Darcy E. P. Telenko, John Atkins, and Nick Dufault, and published by the UF Department of Plant Pathology, January 2014.

On-Farm Evaluations of Reduced Input Fungicide Programs in Peanut Fields with Low, Moderate, or High Levels of Disease Risk

ABSTRACT In 2003, 2004, and 2005 standard and reduced input fungicide programs were evaluated throughout the peanut production region of Georgia for control of early leaf spot (Cercospora arachidicola), late leaf spot (Cercosporidium personatum), and southern stem rot (Sclerotium rolfsii). Disease risk was determined for each field based on the cultural practices implemented and ranged from low to high. Six to eight fungicide applications were made in the standard programs, versus three to six applications in reduced programs. Leaf spot ratings were higher for the reduced programs in five of the fourteen trials with substantial defoliation occurring in one trial. Overall, southern stem rot control for the reduced programs was equal to or better than that for the standard program, which could be attributed to the differences in fungicide selection or timing. Pod yields for the reduced programs were equal to or greater than the standard programs in all but one trial. Net returns were higher for the reduced programs in half of the trials; however, the reduced program resulted in lower net returns in one trial in 2004. Our results indicate that reduced input fungicide programs can be used to adequately manage fungal diseases of peanut without compromising yield or profitability, and that the use of cultivars with moderate levels of disease resistance may enhance disease control.

Biological control of southern stem rot caused by Sclerotium rolfsii using Trichoderma harzianum and arbuscular mycorrhizal fungi on Jerusalem artichoke (Helianthus tuberosus L.)

Efficacy of Trichoderma harzianum and the arbuscular mycorrhizal fungus (AMF) Glomus clarum for suppression of southern stem rot caused by Sclerotium rolfsii in Jerusalem artichoke was investigated in Thailand under greenhouse conditions. Experimental factors included two Jerusalem artichoke genotypes (HEL 246 and JA 37), two levels of T. harzianum and G. clarum (inoculated and blank). The biological control agents were added to the potting medium immediately before seedlings of Jerusalem artichoke were transplanted into it; 20 days later, seedlings were inoculated with S. rolfsii by placing infested sorghum seeds at the base of the stem. The combination of cv. HEL 246 with addition of both G. clarum and T. harzianum had the lowest disease incidence (30%) and required the longest time to permanent wilt (11 days after inoculation). Inoculation of cv. JA 37 and HEL 246 with G. clarum alone gave better control of the disease than did inoculation with T. harzianum alone. The results are the first published report of biological control of S. rolfsii on Jerusalem artichoke.

Genotypic variation of resistance to southern stem rot of Jerusalem artichoke caused by Sclerotium rolfsii

Southern stem rot caused by Sclerotium rolfsii is a significant problem of Jerusalem artichoke (Helianthus tuberosus L.) production in Thailand. Resistant varieties are not available. The objective of this study was to investigate genetic variability of Jerusalem artichoke genotypes for resistance to stem rot caused by S. rolfsii. Ninety-one Jerusalem artichoke genotypes were evaluated under greenhouse conditions. Traits evaluated included disease score, lesion length, days to permanent wilting, plant height, shoot dry weight, and root dry weight index. Number of days from inoculation until permanent wilting was the only trait with statistically significant differences among genotypes. Based on this trait, genotypes were categorized into two distinct groups: resistant and susceptible. Genotypes that consistently expressed relative resistance to S. rolfsii included HEL 280, HEL 278, HEL 293 and JA 98. These genotypes may be useful to plant breeders as sources of germplasm for incorporating resistance to S. rolfsii into Jerusalem artichoke.

Row Pattern and Seeding Rate Effects on Agronomic, Disease, and Economic Factors in Large-Seeded Runner Peanut

ABSTRACT Recent peanut cultivar releases are trending to a larger seed size, but have great resistance to tomato spotted wilt virus (TSWV). Larger-seeded cultivars cost more to plant than smaller at an equivalent population. Reduced seeding rates could save growers on seed costs and impede the spread of southern stem rot, but can reduce plant stands which can lower yields and increase TSWV incidence. Therefore, the objectives of this experiment were to compare seven peanut cultivars (Georgia Green, Georgia-06G, AT 3085RO, Florida-07, Tifguard, AP-3, and Georgia-03L) in single and twin row patterns at three seeding rates (17, 20, and 23 seed/m) on a sandy loam soil at Plains, GA for disease incidence, agronomic, and economic performance. Measured variables included yield and grade, plant height and stand, TSWV and southern stem rot incidence, and adjusted net revenue in 2008 and 2009. Twin rows outperformed single rows whenever differences occurred. The only factors consistently affected by reducing seeding rate were plant height and stand, both decreased at the lowest seeding rate. There was a trend toward lower yields (approximately 6% reduction) at the 17 seed/m rate in twin row pattern, although net returns were not diminished compared to the higher seeding rates since lower seed costs offset yield reductions. The cultivars Georgia-06G and Florida-07 had the highest yield and adjusted net revenue among the seven cultivars in both years. Tifguard and Georgia Green had lowest overall yields and would not be preferred cultivars in sandy loam soils. This study demonstrates that twin rows have higher yield, plant stands, and net revenue, plus reduced TSWV incidence than single row pattern, and a reduction in seeding rate to 17 seed/m can be made without serious risk of lost revenue. However, benefits of reducing seeding rate in twin rows were not as pronounced as they were for single rows, and exhibited a greater potential for lower yield. A grower planting in single rows would likely have the most to gain from planting fewer seed, especially under heavy southern stem rot pressure, but planting in twin rows would still be a preferred option over single rows.

Registration of ‘Bailey’ Peanut

‘Bailey’ (Reg. No. CV‐111, PI 659502) is a large‐seeded virginia‐type peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) with partial resistance to five diseases that occur commonly in the Virginia‐Carolina production area: early leaf spot (caused by Cercospora arachidicola Hori), late leaf spot [caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton], Cylindrocladium black rot [caused by Cylindrocladium parasiticum Crous, M.J. Wingf. & Alfenas], Sclerotinia blight (caused by Sclerotinia minor Jagger), and tomato spotted wilt (caused by Tomato spotted wilt tospovirus). It also has partial resistance to southern stem rot (caused by Sclerotium rolfsii Sacc.). Bailey was developed as part of a program of selection for multiple‐disease resistance funded by growers, seedsmen, shellers, and processors. Bailey was tested under the experimental designation N03081T and was released by the North Carolina Agricultural Research Service (NCARS) in 2008. Bailey was tested by the NCARS, the Virginia Agricultural Experimental Station, and five other state agricultural experiment stations and the USDA‐ARS units participating in the Uniform Peanut Performance Tests. Bailey has an alternate branching pattern, an intermediate runner growth habit, medium green foliage, and high contents of fancy pods and medium virginia‐type seeds. It has approximately 34% jumbo and 46% fancy pods, seeds with tan testas and an average weight of 823 mg seed−1, and an extra large kernel content of approximately 42%. Bailey is named in honor of the late Dr. Jack E. Bailey, formerly the peanut breeding project's collaborating plant pathologist.

Analysis of Gene Expression Profiles in Leaf Tissues of Cultivated Peanuts and Development of EST-SSR Markers and Gene Discovery.

Peanut is vulnerable to a range of foliar diseases such as spotted wilt caused by Tomato spotted wilt virus (TSWV), early (Cercospora arachidicola) and late (Cercosporidium personatum) leaf spots, southern stem rot (Sclerotium rolfsii), and sclerotinia blight (Sclerotinia minor). In this study, we report the generation of 17,376 peanut expressed sequence tags (ESTs) from leaf tissues of a peanut cultivar (Tifrunner, resistant to TSWV and leaf spots) and a breeding line (GT-C20, susceptible to TSWV and leaf spots). After trimming vector and discarding low quality sequences, a total of 14,432 high-quality ESTs were selected for further analysis and deposition to GenBank. Sequence clustering resulted in 6,888 unique ESTs composed of 1,703 tentative consensus (TCs) sequences and 5185 singletons. A large number of ESTs (5717) representing genes of unknown functions were also identified. Among the unique sequences, there were 856 EST-SSRs identified. A total of 290 new EST-based SSR markers were developed and examined for amplification and polymorphism in cultivated peanut and wild species. Resequencing information of selected amplified alleles revealed that allelic diversity could be attributed mainly to differences in repeat type and length in the SSR regions. In addition, a few additional INDEL mutations and substitutions were observed in the regions flanking the microsatellite regions. In addition, some defense-related transcripts were also identified, such as putative oxalate oxidase (EU024476) and NBS-LRR domains. EST data in this study have provided a new source of information for gene discovery and development of SSR markers in cultivated peanut. A total of 16931 ESTs have been deposited to the NCBI GenBank database with accession numbers ES751523 to ES768453.

Use of Resistant Cultivars and Reduced Fungicide Programs to Manage Peanut Diseases in Irrigated and Nonirrigated Fields.

Field experiments were conducted in 2004 and 2005 to evaluate the response of several peanut cultivars to standard and reduced-input fungicide programs under production systems which differed in the duration of crop rotation, disease history within a field, or in the presence or absence of irrigation. Effects on early leaf spot (caused by Cercospora arachidicola), late leaf spot (caused by Cercosporidium personatum), and southern stem rot (caused by Sclerotium rolfsii), pod yields, and economic returns were assessed. Standard fungicide programs were similar for both sets of experiments and included applications of pyraclostrobin, tebuconazole, azoxystrobin, or chlorothalonil. Reduced-fungicide programs, comprising combinations of the aforementioned fungicides, resulted in two and four applications for the cultivar and irrigation experiment, respectively. Two additional programs (a seven-spray chlorothalonil and a nontreated control) were included in the cultivar experiment. Fungicide programs provided adequate levels of leaf spot suppression, and stem rot incidence was similar among fungicide programs within the two management systems. In the cultivar experiment, returns were significantly lower for the reduced program compared with the full program and seven-spray chlorothalonil program; however, they were significantly higher than the nontreated control. Significant differences in leaf spot, stem rot, and yield were observed among cultivars in both experiments. Overall, leaf spot intensity was lowest for the cvs. Georgia-03L and Georgia-01R and greatest for Georgia Green and Georgia-02C. Georgia-03L, Georgia-02C, and AP-3 consistently had lower incidence of stem rot than the other cultivars. Pod yields for all cultivars were equivalent to or greater than Georgia Green in both experiments; however, the performance of reduced-fungicide programs was inconsistent.

Host status of tropical spiderwort (Commelina benghalensis) for nematodes

Abstract Nematodes are the most damaging pathogens of cotton and one of the most important pathogens of peanut. Weeds can support nematode reproduction and reduce the effectiveness of crop rotation as a management tool. This study documents the relative host status of tropical spiderwort for (1) the reniform nematode and the southern and peanut root-knot nematodes and (2) the fungal pathogen southern stem rot. A reproductive factor (RF) was calculated for each nematode (final number divided by initial number). Galling was estimated (0–10 scale) for the root-knot species. The southern root-knot nematode reproduced well on tropical spiderwort, with a gall rating of 3.1 and an RF of 15.5. The peanut root-knot nematode also reproduced well on tropical spiderwort, with a gall rating of 2.1 and an RF of 7.2. Trials with the reniform nematode were analyzed independently. In the first trial with the reniform nematode, the RF was 2.4 on tropical spiderwort and 1.4 on cotton. In the second trial, the RF was 3.6 on ...

Comparison of Calendar and AU-Pnut Advisory Programs with Azoxystrobin for the Control of Leaf Spot and Southern Stem Rot on Peanut1

Abstract In the southeastern U.S., early and late leaf spot diseases can cause substantial pod losses in peanut production. These losses are minimized with frequent fungicide applications through t...