Effect of Compost Amendments on Disease Severity and Yield of Tomato in Conventional and Organic Production Systems

Photosensitizer to the rescue: in planta and field application of photodynamic inactivation against plant pathogenic bacteria

Control of plant pathogens using chemical and synthetic pesticides raises a major safety concern for humans and the environment. Despite the ongoing exploration of sustainable alternative methods, management practices for pathogens, especially bacteria, have remained almost unchanged over decades, whereby long-term uses of copper and antibiotics has led to widespread bacterial resistance in the field. Antimicrobial photodynamic inactivation (aPDI) of bacteria is emerging as an alternative strategy to combat resistant plant pathogens. aPDI utilizes light-sensitive molecules (photosensitizers) that upon illumination produce reactive oxygen species able to kill pathogens. Here we explore the potential of an anionic semisynthetic water-soluble derivative of chlorophyl (Sodium Magnesium Chlorophyllin: Mg-chl), as an antibacterial agent in planta, by simulating processes naturally occurring in the field. Mg-chl in combination with Na2EDTA (cell wall permeabilizing agent) was able to effectively inhibit Pseudomonas syringae pv. tomato DC3000 in vitro and in planta in both tomato and N. benthamiana. Notably, Mg-chl in combination with Na2EDTA and the common surfactant Morwet D-400 significantly reduced Xanthomonas hortorum pv. gardneri and Xanthomonas fragarie, respectively, in a commercial greenhouse trial against bacterial spot disease in tomato and in field experiments against angular leaf spot disease in strawberries.

Organic Amendments for Pathogen and Nematode Control

The loss of methyl bromide as a soil fumigant and minimal advances in the development and registration of new chemical fumigants has resulted in a resurgence of interest in the application of organic amendments (OAs) for soilborne plant pathogen and plant-parasitic nematode management. Significant progress has been made in the characterization of OAs, application of strategies for their use, and elucidation of mechanisms by which they suppress soilborne pests. Nonetheless, their utility is limited by the variability of disease control, expense, and the logistics of introducing them into crop production systems. Recent advances in molecular techniques have led to significant progress in the elucidation of the role of bacteria and fungi and their metabolic products on disease suppression with the addition of OAs. Biosolarization and anaerobic soil disinfestation, developed to manipulate systems and favor beneficial microorganisms to maximize their impact on plant pathogens, are built on a strong historical research foundation in OAs and the physical, chemical, and biological characteristics of disease-suppressive soils. This review focuses on recent applications of OAs and their potential for the management of soilborne plant pathogens and plant-parasitic nematodes, with emphasis primarily on annual fruit and vegetable production systems.

Organic versus Conventional Cropping Sustainability: A Comparative System Analysis

We are at a pivotal time in human history, as the agricultural sector undergoes consolidation coupled with increasing energy costs in the context of declining resource availability. Although organic systems are often thought of as more sustainable than conventional operations, the lack of concise and widely accepted means to measure sustainability makes coming to an agreement on this issue quite challenging. However, an accurate assessment of sustainability can be reached by dissecting the scientific underpinnings of opposing production practices and crop output between cropping systems. The purpose of this review is to provide an in-depth and comprehensive evaluation of modern global production practices and economics of organic cropping systems, as well as assess the sustainability of organic production practices through the clarification of information and analysis of recent research. Additionally, this review addresses areas where improvements can be made to help meet the needs of future organic producers, including organic-focused breeding programs and necessity of coming to a unified global stance on plant breeding technologies. By identifying management strategies that utilize practices with long-term environmental and resource efficiencies, a concerted global effort could guide the adoption of organic agriculture as a sustainable food production system.

Intervals and Number of Applications of Acibenzolar-S-Methyl for the Control of Bacterial Spot on Processing Tomato

Acibenzolar-S-methyl (ASM) is a plant activator that triggers systemic acquired resistance that is labeled for use in Brazil for managing tomato bacterial spot. The aim of this study was to define the optimum relationship between interval and number of applications of ASM for the most efficacious control of bacterial spot on processing tomato. Four intervals between applications (4, 7, 10, and 14 days) and four application frequencies (4, 6, 8, and 10 applications) were evaluated in five trials performed between 2010 and 2011 in Brasília, Distrito Federal, and in Morrinhos, in the state of Goiás. Copper hydroxide (CH) was applied after ASM applications to complete 13 applications per growing season. Two check treatments were added: standard CH weekly applications and untreated. The following variables were evaluated: severity of bacterial spot, yield, percentage of ripe and rotten fruit, soluble solids content, and the benefit/cost ratio. Disease severity varied between treatments in three trials and yield varied in two trials. A greater number of applications resulted in a reduction of bacterial spot, and the ideal interval between applications was between 8 to 10 days. However, there was a reduction in yield with 10 ASM applications. The temporal effect of ASM applications on bacterial spot severity was evaluated under greenhouse conditions. Reduction in disease severity was observed up to 6 days following ASM application. Additionally, the weekly treatment of seven applications of ASM followed by six applications of CH was compared with a standard program of CH under commercial production conditions in Itaberaí, Goiás, where bacterial spot occurred naturally. The program with ASM and CH resulted in significantly less foliar disease severity than the standard program, which did not result in yield gains. In addition, no differences were detected between the two programs for soluble solids content, industrial yield, plant height, and percentage of ripe and rotten fruit.

Plant Diseases and Management Approaches in Organic Farming Systems

Organic agriculture has expanded worldwide. Numerous papers were published in the past 20 years comparing plant diseases in organic and conventional crops. Root diseases are generally less severe owing to greater soil health, whereas some foliar diseases can be problematic in organic agriculture. The soil microbial community and nitrogen availability play an important role in disease development and yield. Recently, the focus has shifted to optimizing organic crop production by improving plant nutrition, weed control, and plant health. Crop-loss assessment relating productivity to all yield-forming and -reducing factors would benefit organic production and sustainability evaluation.

Menadione Sodium Bisulphite (MSB) enhances the resistance response of tomato, leading to repel mollusc pests

BACKGROUND

Snails and slugs are terrestrial gastropods representing an important biotic stress that adversely affects crop yields. These pests are typically controlled with molluscicides, which produce pollution and toxicity and further induce the evolution of resistance mechanisms, making pest management even more challenging. In our work, we have assessed the efficacy of two different plant defence activators, menadione sodium bisulphite (MSB) and 1,2,3-benzothiadiazole-7-thiocarboxylic acid S-methyl ester (BTH), as inducers of resistance mechanisms of the model plant for defence, Solanum lycopersicum, against the generalist mollusc Theba grasseti (Helicidae). The study was designed to test the feeding behaviour and choice of snails, and also to analyse the expression profile of different genes specifically involved in defence against herbivores and wounds.

RESULTS

Our data suggest that, through the downregulation of the terpene volatile genes and the production of proteinase inhibitors, treated MSB plants may be less apparent to herbivores that use herbivore-induced plant volatiles for host location. By contrast, BTH was not effective in the treatment of the pest, probably owing to an antagonistic effect derived from the induction of both salicylic-acid-dependent and jasmonic-acid-dependent pathways.

CONCLUSIONS

This information is crucial to determine the genetic basis of the choice of terrestrial gastropod herbivores in tomato, providing valuable insight into how the plant defence activators could control herbivore pests in plants. Our work not only reports for the first time the interaction between tomato and a mollusc pest but also presents the action of two plant defence inductors that seems to produce opposed responses by inducing resistance mechanisms through different defence pathways.

Plant disease management in organic farming systems

Organic farming (OF) has significantly increased in importance in recent decades. Disease management in OF is largely based on the maintenance of biological diversity and soil health by balanced crop rotations, including nitrogen-fixing and cover crops, intercrops, additions of manure and compost and reductions in soil tillage. Most soil-borne diseases are naturally suppressed, while foliar diseases can sometimes be problematic. Only when a severe disease outbreak is expected are pesticides used that are approved for OF. A detailed overview is given of cultural and biological control measures. Attention is also given to regulated pesticides. We conclude that a systems approach to disease management is required, and that interdisciplinary research is needed to solve lingering disease problems, especially for OF in the tropics. Some of the organic regulations are in need of revision in close collaboration with various stakeholders.

Effect of Aerated Compost Tea on the Growth Promotion of Lettuce, Soybean, and Sweet Corn in Organic Cultivation

This study investigated the chemical characteristics and microbial population during incubation of four kinds of aerated compost teas based on oriental medicinal herbs compost, vermicompost, rice straw compost, and mixtures of three composts (MOVR). It aimed to determine the effects of the aerated compost tea (ACT) based on MOVR on the growth promotion of red leaf lettuce, soybean and sweet corn. Findings showed that the pH level and EC of the compost tea slightly increased based on the incubation time except for rice straw compost tea. All compost teas except for oriental medicinal herbs and rice straw compost tea contained more NO(-) 3-N than NH(+) 4-N. Plate counts of bacteria and fungi were significantly higher than the initial compost in ACT. Microbial communities of all ACT were predominantly bacteria. The dominant bacterial genera were analyzed as Bacillus (63.0%), Ochrobactrum (13.0%), Spingomonas (6.0%) and uncultured bacterium (4.0%) by 16S rDNA analysis. The effect of four concentrations, 0.1%, 0.2%, 0.4% and 0.8% MOVR on the growth of red leaf lettuce, soybean and sweet corn was also studied in the greenhouse. The red leaf lettuce with 0.4% MOVR had the most effective concentration on growth parameters in foliage part. However, 0.8% MOVR significantly promoted the growth of root and shoot of both soybean and sweet corn. The soybean treated with higher MOVR concentration was more effective in increasing the root nodule formation by 7.25 times than in the lower MOVR concentrations Results indicated that ACT could be used as liquid nutrient fertilizer with active microorganisms for culture of variable crops under organic farming condition.

Soil health paradigms and implications for disease management

Soil health has been defined as the capacity of soil to function as a vital living system to sustain biological productivity, maintain environmental quality, and promote plant, animal, and human health. Building and maintaining soil health are essential to agricultural sustainability and ecosystem function. Management practices that promote soil health, including the use of crop rotations, cover crops and green manures, organic amendments, and conservation tillage, also have generally positive effects on the management of soilborne diseases through a number of potential mechanisms, including increasing soil microbial biomass, activity, and diversity, resulting in greater biological suppression of pathogens and diseases. However, there also may be particular disease issues associated with some soil health management practices. In this review, research and progress made over the past twenty years regarding soil health, sustainability, and soil health management practices, with an emphasis on their implications for and effects on plant disease and disease management strategies, are summarized.

Summer heat and low soil organic matter influence severity of hazelnut Cytospora canker

Cytospora canker, caused by the fungus Cytospora corylicola, is present in hazelnut production areas worldwide. The disease is widespread throughout the main production areas of Italy. The causal agent is considered to be a secondary invader of damaged tissue that attacks mainly stressed plants. However, little is known of disease severity and stress factors that predispose plants to infection. In particular, the role of pedoclimatic factors was investigated. Direct survey indicated that disease severity varied across several study sites. Geostatistics showed a strong positive correlation between disease severity index and summer heat (r = 0.80 and 0.91 for July and August, respectively) and strong negative correlation between disease severity index and soil organic matter (r = -0.78). A moderate positive correlation between disease severity index and magnesium/potassium ratio (r = 0.58) and moderate negative correlations between disease severity index and total soil nitrogen (r = -0.53), thermal shock (r = -0.46), and rainfall (r = -0.53) were determined. No significant correlation between disease severity index and soil aluminum (r = -0.35), soil pH (r = -0.01), and plant age (r = -0.38) was found.

Organically managed soils reduce internal colonization of tomato plants by Salmonella enterica serovar Typhimurium

A two-phase experiment was conducted twice to investigate the effects of soil management on movement of Salmonella enterica Typhimurium in tomato plants. In the first phase, individual leaflets of 84 tomato plants grown in conventional or organic soils were dip inoculated two to four times before fruiting with either of two Salmonella Typhimurium strains (10(9) CFU/ml; 0.025% [vol/vol] Silwet L-77). Inoculated and adjacent leaflets were tested for Salmonella spp. densities for 30 days after each inoculation. Endophytic bacterial communities were characterized by polymerase chain reaction denaturing gradient gel electrophoresis before and after inoculation. Fruit and seed were examined for Salmonella spp. incidence. In phase 2, extracted seed were planted in conventional soil, and contamination of leaves and fruit of the second generation was checked. More Salmonella spp. survived in inoculated leaves on plants grown in conventional than in organic soil. The soil management effect on Salmonella spp. survival was confirmed for tomato plants grown in two additional pairs of soils. Endophytic bacterial diversities of tomato plants grown in conventional soils were significantly lower than those in organic soils. All contaminated fruit (1%) were from tomato plants grown in conventional soil. Approximately 5% of the seed from infested fruit were internally contaminated. No Salmonella sp. was detected in plants grown from contaminated seed.

Composting projects under the Clean Development Mechanism: sustainable contribution to mitigate climate change

The Clean Development Mechanism (CDM) of the Kyoto Protocol aims to reduce greenhouse gas emissions in developing countries and at the same time to assist these countries in sustainable development. While composting as a suitable mitigation option in the waste sector can clearly contribute to the former goal there are indications that high rents can also be achieved regarding the latter. In this article composting is compared with other CDM project types inside and outside the waste sector with regards to both project numbers and contribution to sustainable development. It is found that, despite the high number of waste projects, composting is underrepresented and a major reason for this fact is identified. Based on a multi-criteria analysis it is shown that composting has a higher potential for contribution to sustainable development than most other best in class projects. As these contributions can only be assured if certain requirements are followed, eight key obligations are presented.

Pyrolysis-gas chromatography/mass spectrometry identification of distinctive structures providing humic character to organic materials

Flash pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS) was used to study the structural transformations of humic fractions formed as a result of composting processes of diverse organic materials (solid wastes of wineries, solid olive-mill wastes, domestic wastes, ovine manures plus straw, and mixtures of animal manures). Sodium hydroxide-extracted total humic-like extracts (THE; humic plus fulvic acids) from the composted and the initial noncomposted wastes and several reference humic and fulvic acids from soils were analyzed. These results were compared with results from previous studies using 13C-cross polarization magic angle spinning-nuclear magnetic resonance (NMR), UV-visible, and fluorescence emission spectroscopies. Alkylbenzenes and alkylphenols predominate in the pyrograms of the soil humic acids, whereas the fulvic acids showed higher contents of phenolic and polysaccharide-derived compounds. The pyrolysates of THE from the composted samples showed an increase in aromatic and nitrogenated structures and a decrease in polysaccharide-derived compounds. The aromatic contents as determined by Py-GC/MS and 13C-NMR were well correlated in the reference humic substances and THE from composted materials (r = 0.99 and 0.94, respectively; P < 0.01) but not in the case of THE from noncomposted materials, probably due to an aliphatic enhancement in the pyrolysates of these samples and other secondary reactions. The content in alkylbenzenes was consistent with the variations found previously for several UV-visible and fluorescence indexes as a function of the degree of humification, suggesting their involvement in structures that are a characteristic feature of the formation and evolution of humic substances.

Detection of high concentrations of organic acids in fish emulsion and their role in pathogen or disease suppression

Fish emulsion (FE) added to a sandy-loam soil at 1 and 2% rates reduced the viability of Verticillium dahliae microsclerotia by 39 and 74% in 1 day, 87 and 98% in 3 days, and 95 and 99% in 6 days, respectively. The immediate kill of microsclerotia indicated that FE contains toxic substances. We found in FE high concentrations (400 mmol/liter) of organic acids, including some known toxicants. Glycolic, acetic, formic, n-butyric, and propionic acids were the major organic acids detected in FE at the proportions of 52.5, 26.9, 7.9, 7.2, and 4.7%, respectively. In solution assays, the viability of V. dahliae microsclerotia treated for 24 h in 1, 2, 5, and 10% FE (pH 3.6 to 3.0) or a mixture of organic acids (pH 4.1 to 3.9) equivalent to the proportions in FE was reduced by 74, 94, 97, and 99% or 81, 91, 98, and 99%, respectively. The viability of microsclerotia was increased when the treatment solutions were buffered to pH 6.0. The organic acids mixtures and formic (0.025%) and acetic (0.1%) acids were toxic to Pythium ultimum. A mixture of organic acids (1, 2, and 4%) provided immediate protection of cucumber seedlings from damping-off in P. ultimum-infested muck and sandy-loam soils but not in peat-based mix. FE (1 and 2%) provided immediate protection of cucumber seedlings from damping-off in an infested muck soil, and disease protection was consistent when planting was delayed for 7, 14, and 28 days after adding FE. FE (1, 2, and 4%) did not provide immediate protection of cucumber seedlings from damping-off in a P. ultimum-infested peat-based mix; however, disease suppression was evident when planting was delayed for 7, 14, and 21 days after adding FE. Real-time polymerase chain reaction analyses of the peat-based mix indicated that the P. ultimum populations in the FE-amended mix declined over time. This study suggests that these organic acids in FE played a major role in pathogen or disease suppression, depending on the soil and substrate.

Biotic interactions, ecological knowledge and agriculture

This paper discusses biotic interactions in agroecosystems and how they may be manipulated to support crop productivity and environmental health by provision of ecosystem services such as weed, pest and disease management, nutrient cycling and biodiversity conservation. Important elements for understanding biotic interactions include consideration of the effects of diversity, species composition and food web structure on ecosystem processes; the impacts of timing, frequency and intensity of disturbance; and the importance of multitrophic interactions. All of these elements need to be considered at multiple scales that depend in part on the range of the movement of the organisms involved. These issues are first discussed in general, followed by an examination of the application of these concepts in agricultural management. The potential for a greater use of ecological management approaches is high; however, owing to the nature of complex interactions in ecosystems, there is some inherent unpredictability about responses to management interventions under different conditions. Such uncertainty needs to be accommodated in the development of recommendations for farm management. This requires an increased emphasis on the effective synthesis of complex and often apparently contradictory information and on field-based adaptive research, monitoring and social learning by farmer/researcher collaborations.

Biological and molecular analyses of the acibenzolar-S-methyl-induced systemic acquired resistance in flue-cured tobacco against Tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is an economically important virus of flue-cured tobacco. Activation of systemic acquired resistance (SAR) by acibenzolar-S-methyl (ASM) in flue-cured tobacco was studied under greenhouse conditions by challenge inoculation with a severe isolate of TSWV. ASM restricted virus replication and movement, and as a result reduced systemic infection. Activation of resistance was observed within 2 days after treatment with ASM and a high level of resistance was observed at 5 days onward. Expression of the pathogenesis-related (PR) protein gene, PR-3, and different classes of PR proteins such as PR-1, PR-3, and PR-5 were detected at 2 days post-ASM treatment which inversely correlated with the reduction in the number of local lesions caused by TSWV. Tobacco plants treated with increased quantities of ASM (0.25, 0.5, 1.0, 2.0, and 4.0 g a.i./7,000 plants) showed increased levels of SAR as indicated by the reduction of both local and systemic infections by TSWV. The highest level of resistance was at 4 g a.i., but this rate of ASM also caused phytotoxicity resulting in temporary foliar spotting and stunting of plants. An inverse correlation between the TSWV reduction and phytotoxicity was observed with the increase of ASM concentration. ASM at the rate of 1 to 2 g a.i./7,000 plants activated a high level of resistance and minimized the phytotoxicity. Use of gibberellic acid in combination with ASM reduced the stunting caused by ASM. Present findings together with previous field experiments demonstrate that ASM is a potential option for management of TSWV in flue-cured tobacco.

Comparison of Muscodor albus Volatiles with a Biorational Mixture for Control of Seedling Diseases of Sugar Beet and Root-Knot Nematode on Tomato

A biorational synthetic mixture of organic components mimicking key antimicrobial gases produced by Muscodor albus was equivalent to the use of live M. albus for control of seedling diseases of sugar beet (Beta vulgaris) caused by Pythium ultimum, Rhizoctonia solani AG 2-2, and Aphanomyces cochlioides. The biorational mixture provided better control than the live M. albus formulation for control of root-knot nematode, Meloidogyne incognita, on tomato (Lycopersicon esculentum). The biorational mixture provided control of damping-off equal to a starch-based formulation of the live fungus for all three sugar beet pathogens, and significantly reduced the number of root-knot galls on tomato roots compared with a barley-based formulation. Rate studies with the biorational mixture showed that 2 and 0.75 µl/cm³ of soil were required to provide optimal control of Rhizoctonia and Pythium damping-off of sugar beet, respectively. Five microliters of biorational mixture per milliliter of water was required for 100% mortality in 24 h for Meloidogyne incognita in in vitro studies. In in vivo studies, 1.67 µl of the biorational mixture/cm³ of sand resulted in fewer root-knot galls than a Muscodor albus infested ground barley formulation applied at 5 g/liter of sand.

Application of Acibenzolar-S-Methyl Enhances Host Resistance in Tomato Against Ralstonia solanacearum

The chemical elicitor acibenzolar-S-methyl (ASM; Actigard 50 WG), which induces systemic acquired resistance (SAR), was investigated to determine the effect on bacterial wilt of tomato caused by Ralstonia solanacearum on moderately resistant cultivars under greenhouse and field conditions. In greenhouse experiments, ASM was applied as foliar spray and/or soil drench (3 μg/ml) before and as foliar spray (30 μg/ml) after transplanting. The chemical elicitor was ineffective in reducing bacterial wilt incidence on susceptible tomato cultivars Equinox and FL 47 when plants were inoculated with R. solanacearum. However, greenhouse studies indicated that ASM significantly enhanced resistance in cultivars with moderate resistance to bacterial wilt such as Neptune and BHN 466. It appeared that ASM-mediated resistance was partially due to prevention of internal spread of R. solanacearum toward upper stem tissues of tomato plants. The effect of ASM on moderately resistant cultivars was consistent in field experiments conducted in 2002 and 2003 in Quincy, FL, where bacterial wilt incidence was significantly reduced in ASM-treated BHN 466 (in 2002), FL 7514 (in 2003), and Neptune (both years) plants. ASM-treated BHN 466 and FL 7514 produced significantly higher tomato yield than the untreated controls. This is the first report of ASM-mediated control of bacterial wilt under field conditions, which suggests that use of this treatment for moderately resistant genotypes may be effective for control of bacterial wilt of tomato.

Isolation and characterization of rhizobacteria from composts that suppress the severity of bacterial leaf spot of radish

ABSTRACT Composts can induce systemic resistance in plants to disease. Unfortunately, the degree of resistance induced seems highly variable and the basis for this effect is not understood. In this work, only 1 of 79 potting mixes prepared with different batches of mature, stabilized composts produced from several different types of solid wastes suppressed the severity of bacterial leaf spot of radish caused by Xanthomonas campestris pv. armoraciae compared with disease on plants produced in a nonamended sphagnum peat mix. An additional batch of compost-amended mix that had been inoculated with Trichoderma hamatum 382 (T(382)), which is known to induce systemic resistance in plants, also suppressed the disease. A total of 11 out of 538 rhizobacterial strains isolated from roots of radish seedlings grown in these two compostamended mixes that suppressed bacterial leaf spot were able to significantly suppress the severity of this disease when used as inoculum in the compost-amended mixes. The most effective strains were identified as Bacillus sp. based on partial sequencing of 16S rDNA. These strains were significantly less effective in reducing the severity of this disease than T(382). A combined inoculum consisting of T(382) and the most effective rhizobacterial Bacillus strain was less effective than T(382) alone. A drench applied to the potting mix with the systemic acquired resistance-inducing chemical acibenzolar-S-methyl was significantly more effective than T(382) in several, but not all tests. We conclude that systemic suppression of foliar diseases induced by compost amendments is a rare phenomenon. Furthermore, inoculation of compost-amended potting mixes with biocontrol agents such as T(382) that induce systemic resistance in plants can significantly increase the frequency of systemic disease control obtained with natural compost amendments.

Effect of Organic Amendments on Soilborne and Foliar Diseases in Field-Grown Snap Bean and Cucumber

Several paper mills in Wisconsin have programs for spreading paper mill residuals (PMR) on land. A growing number of vegetable farmers recognize the agronomic benefits of PMR applications, but there have been no investigations on the use of PMR for control of vegetable crop diseases. Our objective was to determine the effect of PMR amendments on soilborne and foliar diseases of cucumber and snap bean grown on a sandy soil. Raw PMR, PMR composted without bulking agent (PMRC), or PMR composted with bark (PMRBC) were applied annually in a 3-year rotation of potato, snap bean, and pickling cucumber. Several naturally occurring diseases were evaluated in the field, along with in situ field bioassays. All amendments suppressed cucumber damping-off and Pythium blight and foliar brown spot of snap bean. Both composts reduced the incidence of angular leaf spot in cucumber. In a separate field experiment planted with snap bean for two consecutive years, all amendments reduced common root rot severity in the second year. In a greenhouse experiment, the high rate of PMRBC suppressed anthracnose of snap bean. These results suggest that the application of raw and composted PMR to sandy soils has the potential to control several soilborne and foliar diseases.

Suppression of Bacterial Spot of Tomato with Foliar Sprays of Compost Extracts Under Greenhouse and Field Conditions

The efficacy of foliar sprays with compost water extracts (compost extracts) in reducing the severity of bacterial spot of tomato caused by Xanthomonas vesicatoria was investigated. Extracts prepared from composted cow manure, composted pine bark, an organic farm compost, or composted yard waste, applied as foliar sprays on tomato transplants, resulted in a moderate but statistically significant reduction in the severity of bacterial spot. The population of X. vesicatoria in infected leaves was reduced significantly by extracts prepared from composted cow manure. Efficacy of the water extracts was not affected by oxygen concentrations in the suspension during extraction, compost maturity, or sterilization by filtration or autoclaving. The degree of control provided by foliar sprays with the most effective compost extracts did not differ from that obtained with the plant activator acibenzolar-S-methyl. In the field in two growing seasons, foliar sprays with compost water extracts did not reduce the severity of foliar diseases, including bacterial spot. During the 1997 season, when the severity of bacterial spot in the field was high, foliar sprays with compost water extracts significantly reduced the incidence of bacterial spot on tomato fruit. Amending plot soil with several rates of composted yard waste did not lead to additional control of fruit disease over those only sprayed with extracts. Foliar sprays with a mixture of chlorothalonil and copper hydroxide or with acibenzolar-S-methyl reduced the severity of bacterial spot as well as incidence of spot on fruit.

Reduction of Bacterial Spot Disease Severity on Tomato and Pepper Plants with Foliar Applications of Ammonium Lignosulfonate and Potassium Phosphate

Bacterial spot is a serious and persistent disease problem of tomato and bell pepper in both the United States and Canada. Current disease management practices, based primarily on fixed copper bactericides, do not give consistent, effective protection. Foliar applications of ammonium lignosulfonate (ALS), derived from the wood pulping process, and the fertilizer potassium phosphate (KP) were tested for their ability to control this disease under both greenhouse and field conditions. Acibenzolar-S-methyl was included as a control. Greenhouse-grown tomato transplants treated with acibenzolar-S-methyl, 2 or 4% (vol/vol) ALS, 25 mM KP, or 2% ALS plus 10 mM KP and then inoculated with Xanthomonas campestris pv. vesicatoria had significantly less disease than the unprotected controls. Weekly foliar applications of acibenzolar-S-methyl, ALS, or KP significantly reduced disease severity on the foliage of inoculated field-grown tomato and pepper plants; although less disease appeared on the fruit of these plants, the effect was not always statistically significant except for the acibenzolar-S-methyl treatment. Acibenzolar-S-methyl increased the yield of marketable tomato fruit in 2 of 3 years of the study and that of pepper fruit in 1 of 2 years. There was a marked increase in the yield of marketable fruit on all ALS-treated pepper plants in 2001. None of the treatments significantly increased total tomato or pepper yield. ALS and KP had no observable phytotoxic effect on tomato or pepper foliage. Our results indicate that future integrated disease management programs for bacterial spot may be enhanced by including foliar sprays of these two products.