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In North America Amylostereum areolatum (Chaillet ex Fr.) Boidin is a fungal symbiont associated with both the non-native Sirex noctilio Fabricius (Hymenoptera: Siricidae) and less commonly the native Sirex nigricornis Fabricius (Hymenoptera: Siricidae) woodwasps. The relationship between S. noctilio and A. areolatum constitutes a serious threat to pine plantation in the southern hemisphere. Studies have shown evidence of exchange of symbionts between non-native and native Sirex species. Our objectives were 1) to identify and assemble a panel of rDNA intergenic spacer–single nucleotide polymorphisms (IGS-SNPs) for genotyping strains of A. areolatum symbionts associated with Sirex species in North America, and 2) to develop genetic markers for monitoring the spread of specific A. areolatum haplotypes associated with S. noctilio across regions. The IGS-SNPs panel analyzed included haplotypes B1, B2, D1, D2 (from known IGS type B and D), E, and F. Genetic markers and haplotype-specific primers were designed to detect the IGS haplotypes D and E of A. areolatum. We found that haplotype D was absent in A. areolatum from S. nigricornis in Louisiana, while haplotype E was detected in all A. areolatum from S. nigricornis in Canada and Louisiana. Both haplotype D and E were co-detected in approximately 5% of samples from Canada. The IGS-SNP markers detected specific haplotypes accurately. Observing haplotype D in any A. areolatum from the native S. nigricornis likely indicates the presence of the potentially harmful S. noctilo-A. areolatum complex. The work highlights how IGS-SNPs can help in early detection without direct occurrence/observations of the non-native species of concern.

Throughout history a great many plant species have been purposefully transported to new areas around the globe. Horticulture, the promise of new sources of plant material for industry, forage, food, and stabilization of soil are only a few of the motives for the early transcontinental exchange of plants. Many introductions have been beneficial or benign, but some plants introduced into new areas are now considered invasive and detrimentally impact the environment. Triadica sebifera (Chinese Tallowtree; Euphorbiaceae) is an excellent example of the best intentions leading to unanticipated negative effects many decades later. Native to eastern Asia and now naturalized and widespread in many tropical, subtropical, and temperate areas in the world, Chinese Tallowtree has proven to be one of the worst woody invasive plants. It is known for shading out native vegetation, capable of dominating areas following disturbance or even invading previously diverse undisturbed habitats. It is prevalent in the southern United States, especially along the Gulf Coast. Investigations into classical biological control of Chinese Tallowtree have yielded at least 2 promising candidates but have raised objections among beekeepers and beekeeping organizations who prize the quality honey produced from an abundant spring nectar flow. In this overview, we discuss Chinese Tallowtree's invasive characteristics, detrimental effects, potential use as a biomass crop, and demonstrated or potential direct and indirect effects on native and non-native pollinators. We review the current state of identification and screening of biological control agents and present 4 research topics that are would fill gaps in our knowledge of Chinese Tallowtree and pollinators. Classical biological control has the potential to reduce Chinese Tallowtree populations across the landscape, which would likely result in greater understory and tree diversity, benefitting native and exotic pollinators.

We investigated the antifungal activities of an endophytic fungus identified as Acaromyces ingoldii, found on a loblolly (Pinus taeda L.) pine bolt in Louisiana during routine laboratory microbial isolations. The specific objectives were to determine the inhibitory properties of A. ingoldii secondary metabolites (crude extract) on the mycelial growth of a brown-rot fungus Gloeophyllum trabeum and a white-rot fungus Trametes versicolor, and to determine the effective concentration of A. ingoldii crude preparation against the two decay fungi in vitro. Results show the crude preparation of A. ingoldii from liquid culture possesses significant mycelial growth inhibitory properties that are concentration dependent against the brown-rot and white-rot fungi evaluated. An increase in the concentration of A. ingoldii secondary metabolites significantly decreased the mycelial growth of both wood decay fungi. G. trabeum was more sensitive to the inhibitory effect of the secondary metabolites than T. versicolor. Identification of specific A. ingoldii secondary metabolites, and analysis of their efficacy/specificity warrants further study. Findings from this work may provide the first indication of useful roles for Acaromyces species in a forest environment, and perhaps a future potential in the development of biocontrol-based wood preservation systems.

Throughout history a great many plant species have been purposefully transported to new areas around the globe. Horticulture, the promise of new sources of plant material for industry, forage, food, and stabilization of soil are only a few of the motives for the early transcontinental exchange of plants. Many introductions have been beneficial or benign, however, some plants introduced into new areas are now considered invasive and detrimentally impact the environment. Chinese tallowtree [Triadica sebifera (L.) Small] (Euphorbiaceae) is an excellent example of the best intentions leading to unanticipated negative effects many decades later. Native to eastern Asia and now naturalized and widespread in many tropical, subtropical, and temperate areas in the world, Chinese tallowtree has proven to be one of the worst woody invasive plants. It is known for shading out native vegetation, capable of dominating areas following disturbance or even invading previously diverse undisturbed habitats. It is prevalent in the southern United States, especially along the Gulf Coast. Investigations into classical biological control of Chinese tallowtree have yielded at least two promising candidates but have raised objections among beekeepers and beekeeping organizations who prize the quality honey produced from an abundant spring nectar flow. In this review we discuss Chinese tallowtree’s invasive characteristics, detrimental effects, potential use as a biomass crop, and demonstrated or potential direct and indirect effects on native and non-native pollinators. We review the current state of identification and screening of biological control agents. Four research questions are presented which are designed to fill gaps in our knowledge of Chinese tallowtree and pollinators. We conclude that classical biological control efforts to reduce Chinese tallowtree populations are justified and, if successful, will likely improve habitat for native plants and native and exotic pollinators in restored areas.

Laurel wilt is a destructive disease of redbay (Persea borbonia) and other species in the laurel family (Lauraceae). It is caused by Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus (Coleoptera: Curculionidae), cointroduced into the United States around 2002. During assessments of fungi associated with bark beetles from loblolly pine, an unknown fungus was isolated that appeared to have broad-spectrum antifungal activities. In this study, we identified the unknown fungus and determined the inhibitory effect of its secondary metabolites on R. lauricola. DNA analysis identified the fungus as Acaromyces ingoldii (GenBank accession no. EU770231). Secondary metabolites produced by the A. ingoldii completely inhibited R. lauricola mycelial growth on potato dextrose agar (PDA) plates preinoculated with A. ingoldii and reduced R. lauricola growth significantly on malt extract agar plates preinoculated with A. ingoldii. R. lauricola isolates inoculated on PDA plates 7 days after A. ingoldii were completely inhibited with no growth or spore germination. Direct evaluation of A. ingoldii crude extract on R. lauricola spores in a multi-well culture plate assay showed inhibition of spore germination at 10% and higher concentrations. Secondary metabolites from A. ingoldii could be potentially useful in managing the future spread of laurel wilt.

In the past two decades, laurel wilt disease has significantly affected members of the Lauraceae in the southeast United States, causing widespread mortality of native redbay (Persea borbonia (L.) Spreng), and incidence of infections in avocado (Persea americana Mill.), sassafras (Sassafras albidum L.) and swamp bay (Persea palustris [Raf.] Sarg.) (Fraedrich et al., 2008, 2015, Olatinwo, et al. 2019). Laurel wilt is a vascular disease caused by Raffaelea lauricola (T.C. Harr., Fraedrich & Aghayeva), a fungus vectored by a non-native ambrosia beetle Xyleborus glabratus Eichhoff (Fraedrich et al. 2008). In August 2020, we investigated the mortality of a spicebush shrub (Lindera benzoin L.) (3.8 cm diameter at root collar, two m height) located ca. 17 mi northeast of Colfax, Grant Parish, Louisiana (31.750263° N, -92.643694° W). Evaluation of the dead shrub revealed brown, persistent foliage, and black vascular discoloration of the sapwood, typical symptoms of laurel wilt (Fig. S1). Although, beetle holes were observed on the sapwood, no beetle was found in galleries at the time. In the laboratory, a fungus consistently isolated from surface-sterilized sapwood tissues plated on potato dextrose agar (PDA) was identified as R. lauricola based on the morphological characteristics of the isolate (i.e., mucoid growth, conidiophores, and oblong/ovoid shape conidia [Harrington et al. 2008]). The fungal isolate was denoted as SB1. The identity of the fungus was confirmed by positive PCR amplification of the large subunit ribosomal RNA gene region using species-specific primers; rab-lsu-rl_F: CCCTCGCGGCGTATTATAG and rab-lsu-rl_R: GCGGGGCTCCTACTCAAA (Olatinwo, unpublished). The sequence of the isolate SB1 (GenBank Accession no. MW207371) showed 100% homology to the R. lauricola strain CBS 127349 sequence (GenBank Accession no. MH877933). The pathogenicity of SB1 on spicebush was evaluated on four healthy shrubs (average: 1 m height and 40 mm in diameter) at the location from which the original detection was made. Stems of two spicebush shrubs were inoculated with SB1 agar plugs from a 14-day old culture on PDA, while plain PDA plugs were used on the remaining two shrubs as non-inoculated controls. Agar plugs were placed in 5 mm (0.2 in) diameter hole punched on the bark with cork-borer as described by Mayfield et al (2008). After six weeks, the R. lauricola inoculated shrubs were wilted with noticeable blackened tissue discoloration in the sapwood, while the control trees remained healthy (Fig. S2). Raffaelea lauricola was re-isolated from tissue of the two inoculated, symptomatic shrubs, but not from the control trees. The sequence of the re-isolated R. lauricola isolate, denoted as SB3 (GenBank Accession no. MW207372), showed 100% homology to the R. lauricola strain CBS 127349 and isolate SB1. This first documentation of laurel wilt on spicebush in Louisiana is significant because, spicebush berries, leaves, and twigs are food sources for forest animals, birds, and insects including whitetail deer and spicebush swallowtail (Papilio troilus L.). Since its first report on sassafras in 2014 (Fraedrich et al. 2015), laurel wilt has spread across Louisiana on sassafras and swamp bay (Olatinwo et al. 2019) and has been confirmed in14 parishes. This report shows the relentless nature of the disease, as the pathogen moves from one vulnerable host to the next, expanding into new locations and threatening forest ecosystems across the southern United States.

We report the association of Cristulariella moricola (Hino) Redhead with a zonate leaf spot on Eucalyptus benthamii (Myrtaceae). We observed the disease outbreak across a series of experimental E. benthamii plantings in Barnwell County, South Carolina, USA in October 2015. The disease caused nearly complete foliar necrosis of most trees in one experimental planting, but disease incidence remained at low levels ( C. moricola in other tree species.

We investigated the antifungal activities of an endophytic fungus identified as Acaromyces ingoldii, found on a loblolly (Pinus taeda L.) pine bolt in Louisiana during routine laboratory microbial isolations. The specific objectives were to determine the inhibitory properties of A. ingoldii secondary metabolites (crude extract) on the mycelial growth of a brown-rot fungus Gloeophyllum trabeum and a white-rot fungus Trametes versicolor, and to determine the effective concentration of A. ingoldii crude preparation against the two decay fungi in vitro. Results show the crude preparation of A. ingoldii from liquid culture possesses significant mycelial growth inhibitory properties that are concentration dependent against the brown-rot and white-rot fungi evaluated. An increase in the concentration of A. ingoldii secondary metabolites significantly decreased the mycelial growth of both wood decay fungi. G. trabeum was more sensitive to the inhibitory effect of the secondary metabolites than T. versicolor. Identification of specific A. ingoldii secondary metabolites, and analysis of their efficacy/specificity warrants further study. Findings from this work may provide the first indication of useful roles for Acaromyces species in a forest environment, and perhaps a future potential in the development of biocontrol-based wood preservation systems.

Armillaria root and butt diseases, which are a global issue, can be influenced by changing environmental conditions. Armillaria gallica is a well-known pathogen of diverse trees worldwide (Brazee and Wick 2009). Besides A. gallica causing root rot of Hemerocallis sp. and Cornus sp. in South Carolina (Schnabel et al. 2005), little is reported on the distribution and host range of A. gallica in the southeastern USA. In July 2017, three Armillaria isolates were obtained from two naturally occurring hosts in Georgia, USA and cultured on malt extract medium (3% malt extract, 3% dextrose, 1% peptone, and 1.5% agar). One isolate (GA3) was obtained in Unicoi State Park near Helen, Georgia (Lat. 34.712275, Long. -83.727765, elev. 498 m) from the basal portion of Rhododendron sp. with extensive root/butt decay, but no crown symptoms were evident (Supplementary Figure 1). GA4 and GA5 (Lat. 33.902433, Long. -83.382453, elev. 215 m) were isolated from wind-felled Quercus rubra (red oak) with root disease at the State Botanical Gardens in Athens, Georgia. GA4 was associated with a large root ball (ca. 4-m diameter) (Supplementary Figure 2), and GA5 was obtained from a mature tree with infected roots, with characteristic spongy rot of Armillaria root disease. Crown symptoms could not be evaluated because the crowns had been removed before the collections. Several other oaks with Armillaria root disease were noted throughout the State Botanical Gardens. Pairing tests reduced these three isolates (whiteish mycelia with a dark, brownish crust and rhizomorphs), to two genets with GA4 = GA5. Both genets (GA3 and GA4) were identified as A. gallica using translation elongation factor 1α (tef1) sequences (Genbank Nos. MT761697 and MT761698, respectively) that showed ≥ 97% identity (≥ 98% coverage) with A. gallica sequences (KF156772, KF156775). Also, nine replications of somatic pairing tests showed 33 - 67% compatibility with A. gallica (occurs in southeastern USA), compared with 0 - 22% for A. mexicana, A. mellea (occurs in southeastern USA), A. solidipes, and Desarmillaria tabescens (occurs in southeastern USA). To our knowledge, this note represents the first report of A. gallica on Rhododendron and Q. rubra in Georgia, USA, which has experienced severe drought in recent decades (e.g., Park Williams et al. 2017) that could predispose trees to Armillaria infection (e.g., Wargo 1996). Quercus rubra was previously reported as a host of A. gallica in Arkansas (Kelley et al. 2009) and Massachusetts (Brazee and Wick 2009), USA. In Missouri, USA, A. gallica has been reported as a weak pathogen with potential biological control against A. mellea (Bruhn et al. 2000). Other reports from several regions on various hosts suggest pathogenicity of A. gallica is associated with changing climate (Nelson et al. 2013, Kim et al. 2017, Kubiak et al. 2017). Wide genetic variation and/or cryptic speciation within A. gallica may account for differences in ecological behavior (Klopfenstein et al. 2017), but this is difficult to evaluate because Armillaria pathogenicity tests cannot be used on most forest tree seedlings. This study suggests that A. gallica is more widespread than previously known and its adverse impacts on woody plants may intensify over time, depending on the environmental conditions. Further studies are needed to determine environmental influences on A. gallica, the full distribution of A. gallica, and its effects in forests of the southeastern USA.

In recent years, outbreaks of nonnative invasive insects and pathogens have caused significant levels of tree mortality and disturbance in various forest ecosystems throughout the United States. Laurel wilt, caused by the pathogen Raffaelea lauricola (T.C. Harr., Fraedrich and Aghayeva) and the primary vector, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff), is a nonnative pest-disease complex first reported in the southeastern United States in 2002. Since then, it has spread across eleven southeastern states to date, killing hundreds of millions of trees in the plant family Lauraceae. Here, we examine the impacts of laurel wilt on selected vulnerable Lauraceae in the United States and discuss management methods for limiting geographic expansion and reducing impact. Although about 13 species belonging to the Lauraceae are indigenous to the United States, the highly susceptible members of the family to laurel wilt are the large tree species including redbay (Persea borbonia (L.) Spreng) and sassafras (Sassafras albidum (Nutt.) Nees), with a significant economic impact on the commercial production of avocado (Persea americana Mill.), an important species native to Central America grown in the United States. Preventing new introductions and mitigating the impact of previously introduced nonnative species are critically important to decelerate losses of forest habitat, genetic diversity, and overall ecosystem value.

International audience; AbstractKey messageAgrilus maceris attacking sugarberry trees in the southeastern USA, a region from which few specimens have been previously collected. Despite attacking at high densities, this species appears to be a secondary pest, and there is no evidence it carries harmful fungal pathogens.ContextBecause the genus Agrilus Curtis includes significant forest pests, the association of a poorly known species, Agrilus macer LeConte, with unexplained sugarberry (Celtis laevigata Willd.) mortality in the southeastern USA is a cause for alarm.AimsThis study sought to investigate the distribution and biology of A. macer and determine whether the species is a primary cause of observed tree mortality.MethodsThrough a series of studies and literature searches, we documented aspects of A. macer biology and distribution while focusing on egg-laying behavior and searching for fungal pathogens associated with oviposition sites.ResultsA. macer appears to be widely distributed throughout the southern USA, but most records are from Texas and Louisiana. Egg mass densities up to 1.2 masses per 10 cm2 (equivalent to ~ 1.9 eggs per cm2) were observed on trunks, branches, and exposed roots of dying C. laevigata trees in our study area, with an average of 16 eggs per mass. Fungi isolated from discolored sapwood around larval galleries did not cause defoliation, dieback, or mortality of sugarberry in inoculation trials.ConclusionOur findings suggest that A. macer is a secondary pest on sugarberry and does not transmit harmful fungal pathogens.

The camphor shot borer, Cnestus mutilatus (Blandford) is a nonnative ambrosia beetle first reported in the United States in 1999 at Oktibbeha County in Mississippi. Although, C. mutilatus is a major pest of several trees in its native habitat in Asia, it is not yet a major pest in the United States. However, the range expansion in recent years across the southeastern region indicates that C. mutilatus could be adapting quickly to the new environment, perhaps because of the availability of numerous host trees and suitable environmental conditions that support the population. As the population increases, future outbreaks of C. mutilatus may result in mortality of valuable hosts. Our objective was to identify potential suitable habitats for C. mutilatus in the southeastern United States under changing climate by 2020 and 2060 by examining C. mutilatus preferred conditions, host environmental requirements, precipitation, and temperature projections from an ensemble of general circulation model, and Intergovernmental Panel on Climate Change future climate scenarios. Our results indicated that suitable habitat for C. mutilatus in the southeastern United States will expand slightly under the A1B emission scenarios (i.e., moderate population growth and high-energy use balanced across all sources), and significantly under B1 emission scenarios (i.e., representing moderate population growth and an emphasis on global approaches to economic and environmental stability) by 2060. Whereas the opposite may occur under the A2 scenario (i.e., representing continuously increasing population, regionally focused economic growth, and slower introduction of alternative fuels technology). Nearly half of the parishes in Louisiana and counties in Mississippi will be suitable for C. mutilatus by 2020, under the A2 emission scenarios. However, suitable habitat range could decrease and become fragmented by 2060. These results could be useful in forest management efforts in places where C. mutilatus may become established in the future.

Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae) and sassafras trees that died from laurel wilt were discovered in a 3-parish area of northern Louisiana, USA, in Sep 2014. Redbay, a species that has been severely affected by the disease in the coastal plains forests of the southeastern USA, is not found in this area of northern Louisiana, suggesting that sassafras is attractive to X. glabratus and an adequate reproductive host for the beetle. This is the first report of X. glabratus and laurel wilt in Louisiana and the first report of the beetle and disease west of the Mississippi River. Sumario En septiembre del 2014, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae) y arboles de sasafras que murieron a causa de la marchitez del laurel fueron descubiertos en un area de 3 municipios del norte de Louisiana, EE.UU. El aguacatillo ( Persea borbonia ), una especie que se ha visto gravemente afectada por la enfermedad en los bosques de la llanura costero del sudeste de EE.UU., no se encuentra en esta zona del norte de Louisiana, lo que sugiere que el sasafras es atractivo para X. glabratus y un hospedero reproductivo adecuado para el escarabajo. Este es el primer informe de X. glabratus y la marchitez del laurel en Louisiana y el primer informe del escarabajo y la enfermedad al oeste del rio Mississippi. View this article in BioOne

The woodwasp Sirex noctilio F. (Hymenoptera: Siricidae) has become established in North America.Aprimary tactic for the management of S. noctilio in the southern hemisphere has been the development of a biological control agent, Deladenus siricidicola Bedding. This nematode has a bicyclic life cycle including a mycetophagous free-living and parasitic cycle. During oviposition, female Sirex woodwasps inject a symbiotic fungus. Because D. siricidicola only develops well on Amylostereum areolatum (Chaillet ex Fries) Boidin (Russulales: Amylostereaceae) and North American woodwasps were thought to all have Amylostereum chailletii (Persoon) Boidin as their fungal symbiont, the risk of unintended impacts from D. siricidicola in North America was considered low. Specific polymerase chain reaction primers were designed to amplify the intergenic spacer region of Amylostereum symbionts in a population of the native woodwasp Sirex nigricornis F. located in central Louisiana (i.e., well outside the known dis...

Sunflower (Helianthus annuus L.) has emerged as an economically important crop in Pakistan due to its significant share in vegetable oil production. The plant metabolic processes require protein to increase the vegetative, reproductive growth and yield of the crop. The protein is wholly dependent upon the amount of nitrogen fertilization available for plant use. A two-year field study was conducted in 2008 and 2009. The objective was to determine the effect of different nitrogen (N) levels (N1 = 0 kg·ha–1, N2 = 60 kg·ha–1, N3 = 120 kg·ha–1, N4 = 180 kg·ha–1 and N5 = 240 kg·ha–1) on three sunflower hybrids (Hysun-33, Hysun-38 and Poineer-64A93) in agro-climatic conditions of Gujranwala, a sub-humid region in the centre of the Punjab province of Pakistan. A randomized complete block design split plot experiment was set-up with cultivars in the main plots and N levels in the subplots. Results showed that Hysun-38 gave maximum TDM (15815 kg·ha–1) and maximum grain yield (3389 kg·ha–1), while minimum TDM (14640 kg·ha–1) and grain yield (3125 kg·ha–1) was observed in Hysun-33. Among different N rates evaluated, N4 gave maximum TDM (17890 kg·ha–1) and grain yield (3809 kg·ha–1) compared to the other N rates. The maximum oil content (46.2%) was observed in Hysun-38 without application of N fertilizer (N1), while the minimum oil content (40.6%) was observed from N5 treatment. In conclusion, the application of 180 kg·ha–1 N to Hysun-38 provided the best combination for good yield in sunflower crop under the prevailing sub-humid conditions of Pakistan.

In the southeastern United States, millions of dollars worth of crop damage associated with tobacco thrips (Frankliniella fusca Hinds) and western flower thrips (Frankliniella occidentalis Pergande) are reported annually for economically important crops such as cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.). Tobacco thrips and western flower thrips are also important vectors of Tomato spotted wilt virus (TSWV). The populations and spread of both thrips species relies on favourable weather conditions, especially prolonged temperatures above a minimum developmental threshold. Accurate local weather information is, therefore, crucial for early prediction of thrips' population dynamics during the spring when thrips' population information could assist farmers in mitigating damage to crops. The objective of this study was to demonstrate the application of the Weather Research and Forecasting (WRF) model predictions for developing high resolution spatial and temporal forecast maps of favourable conditions for thrips' development even for locations where weather stations are not available. Tobacco thrips and western flower thrips were evaluated based on degree-day models. The results showed that southwestern Georgia is more favourable for thrips development during the early part of the growing season, although the rate of development varied according to the thrips species. The maps that were produced using WRF output provided high-resolution forecasts for favourable conditions and scouting guidance in places where weather information was limited. An accurate prediction of pest development based on forecasts of favourable conditions may assist growers in pest management decisions and in timely application of insecticides.

The impact of El Nino – Southern Oscillation (ENSO) on weather patterns could have cascading effects on several diseases of important crops in the southeastern United States. One such disease is spotted wilt of peanut caused by the Tomato spotted wilt virus (TSWV). Significant economic losses have been recorded by peanut growers in the southeastern United States since the disease was first reported in 1986. The virus is transmitted by western flower thrips Frankliniella occidentalis and tobacco thrips, Frankliniella fusca . The objective of this study was to examine the influence of El Nino – Southern Oscillation on spotted wilt intensity and peanut yield. Our analysis was based on field trials conducted between 1994 and 2005 at field locations in Georgia and Florida in the United States. The spotted wilt intensity (%) in two peanut genotypes and the corresponding yield were recorded and evaluated. Each season was categorized by ENSO (El Nino, Neutral or La Nina) based on the NOAA Climate Prediction Center classification scheme. Results showed that the interaction between ENSO and peanut genotypes significantly affected spotted wilt intensity. Spotted wilt intensity was significantly lower during La Nina when compared to El Nino or Neutral years. The results also showed a significant correlation between spotted wilt intensity and peanut yield. Incorporating findings from this study into the existing TWSV risk index could aid peanut producers in making management decisions for reducing spotted wilt.

Peanut growers in the southeastern United States have suffered significant economic losses due to spotted wilt caused by Tomato spotted wilt virus (TSWV). The virus is transmitted by western flower thrips, Frankliniella occidentalis, and tobacco thrips, F. fusca, and was first reported in the southeast in 1986. The severity of this disease is extremely variable in individual peanut fields, perhaps due to the sensitivity of the vector population to changing weather patterns. The objective of this study was to investigate the impact of early spring weather on spotted wilt risk in peanut. On-farm surveys of spotted wilt severity were conducted in Georgia peanut fields in 1998, 1999, 2002, 2004, and 2005. The percent spotted wilt intensity (%) for cv. Georgia Green was recorded and categorized into three intensity levels: low, moderate, and high. Meteorological data were obtained from the Georgia Automated Environmental Monitoring Network for the period between March 1 and April 30. Statistical analysis was conducted to identify weather variables that had significant impact on spotted wilt intensity. The results indicated a high probability of spotted wilt if the number of rain days during March was greater than or equal to 10 days and planting was before 11 May or after 5 June. The total evapotranspiration in April (>127 mm) and the average daily minimum temperature in March (>6.8°C) similarly increased the risk of spotted wilt. Knowing in advance the level of spotted wilt risk expected in a peanut field could assist growers with evaluating management options and significantly improve the impact of their decisions against spotted wilt risk in peanut.

Tomato spotted wilt virus (TSWV), a member of the genus Tospovirus (family Bunyaviridae), is an important plant virus that causes severe damage to peanut (Arachis hypogaea) in the southeastern United States. Disease severity has been extremely variable in individual fields in Georgia, due to several factors including variability in weather patterns. A TSWV risk index has been developed by the University of Georgia to aid peanut growers with the assessment and avoidance of high risk situations. This study was conducted to examine the relationship between weather parameters and spotted wilt severity in peanut, and to develop a predictive model that integrates localized weather information into the risk index. On-farm survey data collected during 1999, 2002, 2004, and 2005 growing seasons, and derived weather variables during the same years were analyzed using nonlinear and multiple regression analyses. Meteorological data were obtained from the Georgia Automated Environmental Monitoring Network. The best model explained 61% of the variation in spotted wilt severity (square root transformed) as a function of the interactions between the TSWV risk index, the average daily temperature in April (TavA), the average daily minimum temperature between March and April (TminMA), the accumulated rainfall in March (RainfallM), the accumulated rainfall in April (RainfallA), the number of rain days in April (RainDayA), evapotranspiration in April (EVTA), and the number of days from 1 January to the planting date (JulianDay). Integrating this weather-based model with the TSWV risk index may help peanut growers more effectively manage tomato spotted wilt disease.

This chapter examines experimental design considerations for a population-based approach for identifying microorganisms involved in specific in situ functions. Although this chapter focuses on a particular population-based approach, many of the experimental design considerations discussed here apply to a wide range of rRNA gene-based population studies and sequence selective PCR assays. This chapter examines an experimental approach that uses the population-based strategy. The approach has the following three phases: (i) identifying populations of rRNA genes whose abundances correlate with the functional parameter, (ii) validating the rRNA gene correlates identified in phase I by using an independent quantitative assay, and (iii) isolating the microorganisms identified by the rRNA gene correlates and reintroducing them into the environment to assess their functions in situ. This approach was recently used to identify microorganisms that suppress the population development of the plant parasitic nematode Heterodera schachtii in southern California soil. Functional gradients are created by manipulating the microbial community with methods such as differential heat treatments, targeted antimicrobial agents, and nutritional amendments. Microbial community composition is examined by rRNA gene analysis. Nucleotide sequence analysis of rRNA gene clone libraries can be used to generate detailed depictions of microbial community composition. PCR assays can be validated by using them to amplify DNAs extracted from different environmental samples and then cloning and sequencing several randomly selected clones from each sample. The assays can be considered selective if they exclusively amplify the target sequence.

Weather information is critical for developing pest models and decision tools that are useful for managing pest problems. It is particularly important for efficient scheduling of pesticide applications, reducing unintended consequences of chemical residues on the ecosystem, and preventing the emergence of pest resistance that follows repeated use of chemical pesticides. Weather-based pest forecasting is therefore crucial for efficient use of pesticides, the overall protection of valuable crops, crop productivity, and economic returns for the farmer. It is also critical for successful implementation of long-term integrated pest management (IPM) strategies. Global access to mobile phones, electronic text messages, emails, and dynamic internet website information have become effective means of instantly communicating pest risk information to farmers, while advances in science and emerging technology are making the output from innovative models such as high-resolution Weather Research and Forecasting (WRF) available for practical use on the farm. In this chapter, the complexity of weather is examined as a key factor in pest management, along with the uncertainty inherent in weather-based models for predicting potential pest risks.

The effects of soil inoculation with A. flavus, variety and cropping system on the level of aflatoxin in stored maize were investigated under crop storage conditions in Benin. The experiment was organized in a factorial scheme (two varieties x two cropping system x with or without A. flavus soil inoculation) with eight treatments carried out in a completely randomized block design with three replications. A. flavus incidence in the plots soil was assessed both before and after soil inoculation. The harvested maize was stored for four months and cobs were sampled in a monthly interval and analyzed for the determination of Fusarium spp. colonization, Penicillium spp. and A. flavus cfu levels, insect pests population size and aflatoxin content. Multi-factorial analysis of variance and linear regression analyses with dummy variables were used to compare treatments. The concentrations of aflatoxin B1 and B2 in the kernels tended to increase with time during storage. Variety and fungal inoculation were the main factors influencing the levels of aflatoxins in stored maize. The improved variety showed a higher number of A. flavus cfu and aflatoxin B1 and B2 levels as compared to the local variety. Intercropping with Vigna unguiculata decreased the aflatoxin concentration in the improved variety but not in the local variety. The local variety had higher levels of Penicillium spp. and lower levels of Fusarium spp. than the improved variety. The treatments had no effect on the populations of the most common storage insect pests, but their levels were positively correlated with aflatoxin content. Both the initial inoculum level and the variety effect on the water content of the kernels after harvest played a significant role in A. flavus infection.

Early leaf spot of peanut (Arachis hypogaea L.), a disease caused by Cercospora arachidicola S. Hori, is responsible for an annual crop loss of several million dollars in the southeastern United States alone. The development of early leaf spot on peanut and subsequent spread of the spores of C. arachidicola relies on favorable weather conditions. Accurate spatio-temporal weather information is crucial for monitoring the progression of favorable conditions and determining the potential threat of the disease. Therefore, the development of a prediction model for mitigating the risk of early leaf spot in peanut production is important. The specific objective of this study was to demonstrate the application of the high-resolution Weather Research and Forecasting (WRF) model for management of early leaf spot in peanut. We coupled high-resolution weather output of the WRF, i.e. relative humidity and temperature, with the Oklahoma peanut leaf spot advisory model in predicting favorable conditions for early leaf spot infection over Georgia in 2007. Results showed a more favorable infection condition in the southeastern coastline of Georgia where the infection threshold were met sooner compared to the southwestern and central part of Georgia where the disease risk was lower. A newly introduced infection threat index indicates that the leaf spot threat threshold was met sooner at Alma, GA, compared to Tifton and Cordele, GA. The short-term prediction of weather parameters and their use in the management of peanut diseases is a viable and promising technique, which could help growers make accurate management decisions, and lower disease impact through optimum timing of fungicide applications.

Olatinwo, R., Borneman, J., and Becker, J. O. 2006. Induction of beetcyst nematode suppressiveness by the fungi Dactylella oviparasitica and Fusarium oxysporum in field microplots. Phytopathology 96:855-859. The ability of Dactylella oviparasitica and Fusarium oxysporum to suppress Heterodera schachtii numbers was examined in field microplots. Fungi were individually added to fumigated field soil that was seeded with sugar beet. Four weeks later, soils were infested with H. schachtii second-stage juveniles (J2). At two harvests, 11 weeks and 19 weeks (1,469 and 2,547 degree days (base 8°C), respectively) after nematodeinfestation, H. schachtii cyst and egg numbers were assessed. At both time points, D. oviparasitica reduced H. schachtii population densities to those in the naturally suppressive soil, even when additional H. schachtii J2 were added to the microplots after the first harvest. Although F. oxysporum did not alter H. schachtii population densities after 11 weeks, significant reductions were detected after 19 weeks. The sustainability of the H. schachtii suppressiveness created by single applications of the fungi at the beginning of the microplot trials was further examined in a greenhouse study. Soil collected at the completion of the microplot trials was potted and seeded with sugar beet. Four weeks later, each pot was infested with H. schachtii J2. Approximately 16 weeks (1,389 degree days) after seeding, the D. oviparasitica-amended soil produced greater fresh root weights and considerably smaller nematode population densities than the nonamended control.

The effects of Dactylella oviparasitica strain 50 applications on sugarbeet cyst nematode (Heterodera schachtii) population densities and plant weights were assessed in four agricultural soils. The fungus was added to methyl iodide-fumigated and nonfumigated portions of each soil. The soils were seeded with Swiss chard. Four weeks later, soils were infested with H. schachtii second-stage juveniles (J2). Approximately 1,487 degree-days after infestation, H. schachtii cyst, egg and J2 numbers and plant weights were assessed. In all four fumigated soils, D. oviparasitica reduced all H. schachtii population densities and increased most of the plant weights compared to the nonamended control soils. In two of the nonfumigated soils (10 and SC), D. oviparasitica reduced H. schachtii population densities and increased most plant weight values compared to the nonamended control soils. For the other two nonfumigated soils (44 and 48), which exhibited pre-existing levels of H. schachtii suppressiveness, fungal applications had relatively little impact on H. schachtii population densities and plant weights. The results from this study combined with those from previous investigations suggest that D. oviparasitica strain 50 could be an effective biological control agent.

An experimental app roach was developed for identifyin g microorganisms involved in spec if ied fun ctions such as path ogen suppress iveness. In thi s approac h, it was postul ated th at the micro organisms involved in path ogen suppress iveness co uld be discovered by identifyin g those orga nisms whose popul ation s positively co rrelate with hi gh levels of suppress iveness. The approac h has thre e phase s. The fir st phase is to identify bacteri al and fungal rRNA genes (rDNA) from so ils possessin g various levels of suppress iveness. Rib osomal DNA sequences that are more abundant in the highly suppress ive so ils than in the less suppress ive soils are considered cand idate sequences. A meth od termed oligonucleotide fin gerprinting of rRNA ge nes (OFRG) is used to obta in extensive analysis of microbi al community composition. The seco nd phase of thi s experimental approac h is to verify the results obtained from phase one usin g quantitative PCR. Here, select ive PCR primers for each of the candidate rDNA sequences are design ed. The se primers are then used to determine the rel ative amounts of the candidate sequences in soils possessin g various levels of suppress iveness produ ced by several different meth ods such as mixing various quantitie s of suppress ive and fumi gation-induced non-suppressive so il, biocid al treatments and temperature tre atments. In phase three, the organisms th at cons istently correlate with suppress iveness are isolated and amended to non-suppressive soils to ass ess their abilit ies to produ ce suppress iveness. The utility of thi s experimental appro ach was dem onstrated by usin g it to identify microorganisms invo lved in suppress iveness again st the plant-p arasitic nematode, Heterodera schachtii. This general experimental approac h sho uld also be useful for the identifying microorganisms involved in fun ctions other then pathogen suppress iveness.