1. Identify natural products and crop production systems that contribute to management of soilborne diseases, weeds, and nematodes. 1a. Develop combinations of commercially-available allylisothiocyanates (AITC) with organic amendments and other crop protection tools to improve weed, disease, and nematode control. 1b. Develop strategies to eliminate obstacles to the use of dimethyl disulfide. 2. Optimize application of anaerobic soil disinfestation (ASD) for application in vegetable and ornamental production. 2.a. Determine minimal input requirements and optimize organic amendments for effective application of ASD. 2.b. Increase environmental benefit of ASD through incorporation of reclaimed water. 3. Identify rootstocks for use with grafted vegetables with resistance or tolerance to pathogens and root-knot nematodes. 3a. Characterize rootstocks and associated microbiome for resistance or tolerance to soilborne pathogens of importance in the Southeastern U.S. 3b. Determine nutritional requirements and capacity of grafted plants to mitigate abiotic stress related to water quality.
The loss of methyl bromide for soil fumigation, limited registration of new chemical fumigants, and increased regulation of existing chemical fumigants has caused significant changes to crop production practices, including the registration and utilization of biofumigants and non-fumigant systems. Newly registered compounds, used alone or in combination, do not provide the same level of pest control resulting from the use of methyl bromide. Recognizing that some of the currently-registered chemical fumigants may, in the future, follow the same path as methyl bromide, the emphasis of the current research project will be to enhance the efficacy and understand the mechanisms of biologically and culturally-based management strategies for pathogens, weeds, and nematodes impacting vegetable and ornamental crops. Efficacy of management components will be examined individually and in combinations to achieve improved control of pathogens previously managed through soil fumigation using methyl bromide and to mitigate abiotic stress. Although some tactics have shown significant efficacy against individual pests or problems, integrated systems that address pest complexes are limited. It is critical that broad-spectrum pest control is achieved and approaches are compatible with the USDA, ARS mission to sustain a competitive agricultural economy by addressing pests that impact crop production as well as improving the health of the agro-ecosystem. Developed strategies will be built upon to gain a better understanding of pest biology, plant nutrition, pathogen and non-pathogen microbial interactions, and the impacts of pest control practices on the development of disease, weed, and nematode suppressive soil. Laboratory, greenhouse, and field experiments will be conducted independently, and in cooperation with ARS and University researchers, and through agreements with industry to broaden the scope of the research. Continued engagement with grower and industry partners will ensure effective transfer of technology which will include more efficient and environmentally compatible crop production systems that minimize health risks to workers and bystanders, and reduce inputs and environmental pollution from pesticides and fertilizers.
This is the final report for this project which has been replaced by 6034-22000-046-000D, "Enhancing Vegetable and Ornamental Production by Synergistically Managing Nutrients and Pests." ARS scientists in Fort Pierce, Florida, conducted field trials to determine the efficacy of allylisothiocyanate (AITC) to manage soil pathogens and pests including nematodes on multiple vegetable and cut flower species. It was shown that AITC, which does not manage weeds, paired well with herbicides for weed control, and still managed soilborne plant pathogenic microbes and plant parasitic nematodes. On-farm field trials were held where chitin amendments in combination with AITC were applied to the soil prior to planting. Microbial deoxyribonucleic acid (DNA) was extracted from soil collected throughout the experiment. Utilizing length heterogeneity polymerase chain reaction (LH-PCR) and sequencing techniques, bacterial community shifts were observed and particularly with Actinomycetes. Field experiments have been completed and data has been collected. On-farm field trials were conducted to determine the effect of chitin products on managing three types of root-knot nematode. Root-knot nematode population densities from three species of cut flowers were calculated along with the marketable yield of the flowers. Dimethyl disulfide (DMDS) was repeatedly applied to a field. Prior to and after application of DMDS soil samples were collected and total DNA was extracted. Utilizing LH-PCR to compare temporal sampling of the bacterial community, it was observed that specific populations increased with continual DMDS application. Adoption of DMDS was limited due to its strong odors. Materials for odor mitigation were identified and small-scale laboratory evaluations have been completed to determine field-applicable rates on chlorine dioxide. Sources of biochar were identified and collected. Oak residue biochar was applied with DMDS and had a significant impact on the detection of dimethyl disulfide through the plastic at the soil surface. The odor mitigation did not detrimentally impact nematode mortality levels, but poor weed control occurred in all treatments. After surveying Florida growers, the cost of molasses was one of the limiting factors for adopting ASD. Thus, multiple field and greenhouse studies were conducted to compare various alternative carbon sources to combine or replace molasses as a soil amendment. These sources included whey, citrus molasses, composted algae, various common weeds, common cover crops, and lactose. These various soil amendments were compared to molasses by measuring the cumulative anaerobicity of the soil over the three-week ASD treatment. While a few alternatives carbon sources created anaerobic conditions similar to molasses, a few drawbacks were discovered upon considering application for large scale operations, such as cost and availability of some amendments for when ASD would be applied. Additionally, ASD experiments were conducted to evaluate the effect of different carbon sources, dry molasses and wheat bran, and increased carbon ratios on the sprouting and growth of introduced Cyperus esculentus (yellow nutsedge) tubers. These treatments were compared to a nonamended control. Wheat bran resulted in significantly fewer sprouted nutsedge tubers as well as a reduction in the number of tubers produced. However, ASD treatments with wheat bran-based amendments at lower C:N ratios reduced tuber sprouting and reproduction. Soil and leachate samples were collected from soil amended with the different carbon sources and compared to molasses amended and non-amended soil. Microbial DNA was extracted from the treated soil and using length heterogeneity pcr (LH-PCR) it was observed that bacterial populations differed depending on the carbon source applied. Soil chemistry, plant nutrient, and leachate have been collected and processed. The elements of ASD were combined with field soil and incubated at 30 Celsius for 7-days. The resulting product was added to field-soil alone and various application of ASD, including full rate and half rate of molasses. The following treatments are listed least anaerobic to most: non-amended soil, product alone, ASD full rate plus product, ASD, and ASD half rate plus product. None of the treatments were detrimental to tomato health. Thus, the cost of ASD could be reduced by reducing the amount of molasses and adding this product. Reclaimed water was collected from seven water treatment facilities at different time points throughout the year. It was observed that nutrients and bacterial populations varied significantly depending on seasons and rainfall. Additionally, after consulting with the water treatment managers, it was discovered that reclaimed water still contained heavy metals and pharmaceutical residue. Experiments were conducted by ARS scientists at Fort Pierce, Florida, to assess the resistance of tomato and cucurbit rootstocks. Heirloom tomato scions were grafted in various combinations to 18 nematode resistant rootstocks. These combinations were planted in commercial fields that had a history of high nematode and Fusarium oxysporum f.sp. lycopersici pressure. Interestingly, nematode resistance was observed to be broken in two fields. In order to determine the cause for the resistance break down, an experiment to determine if foliar disease could induce more stress, thus contributing to nematode resistance breakdown. However, the results were inconclusive due to variability of disease in the field. Another possible explanation was that nematode resistance breakdown was due to higher temperature or rootstocks being overwhelmed by multiple species of root-knot nematodes. Thus, growth chamber experiments were conducted in which grafted tomato plants were grown at different temperatures and inoculated with one or multiple species of root-knot nematode. Temperature did not contribute to resistance breakdown, however mixed nematode populations impact galling. It has been proposed that a diversity of microbes contribute to resistance to pathogens and pests. A series of experiments were conducted to determine if bacterial populations in bulk soil and in the rhizosphere differed between different resistant and susceptible rootstocks. Plants were grafted on each other, resistant rootstock and susceptible scion and vice versa, and self-grafted. Plants were grown until blossoms formed. Microbial DNA was extracted from bulk and rhizosphere soil. Bacterial populations found in the bulk and rhizosphere differed between resistant and susceptible bulk. Maximized telework prevented the initiation of experiments related to the establishment of nutrient use efficiencies of grafted and non-grafted vegetable plants. Bell pepper is the second leading vegetable crop in Florida. The profitability of bell pepper has been endangered by the increasing incidence of Phytophthora capsici, an important soilborne plant-pathogen known for its destructive potential, especially in subtropical areas. While periods of high rainfall and raised water levels are considered major causes of P. capsici outbreaks, the incidence of the disease is also favored by salinity stress, a condition increasingly affecting the coastal areas of South Florida, where a significant amount of bell pepper production occurs. Vegetable grafting is a tool that has the potential to address these issues. Studies were conducted to evaluate plant growth, nutrient accumulation, yield, and stress response of different bell-pepper grafting combinations to P. capsici under increasing salinity conditions. Non-grafted and self-grafted plants of a susceptible pepper cultivar were compared with plants grafted onto resistant rootstocks. In infested soil, non-grafted and self-grafted susceptible plants showed consistently higher incidence of Phytophthora blight compared to those grafted onto resistant rootstocks. Moreover, plants grown under moderate salinity had a higher disease incidence. Irrigation with moderately saline water may increase the incidence of Phytophthora blight in susceptible cultivars of bell pepper, however, commercial rootstocks resistant to P. capsici will control the disease either with no, moderate, or moderately-high salinity levels.
1. Management of weeds and soil-borne pathogens and pests with natural products. ARS scientists in Fort Pierce, Florida investigated three natural products for their potential to manage soilborne biological factors that limit plant health and crop yield. Allylisothiocyanates (AITC) is an organosulfur compound naturally found in mustard and other members of the Brassicaceae family. It has been shown to be a successful bactericide, nematicide and fungicide, yet, has very poor weed control. These ARS scientists showed that AITC could be combined with herbicides to manage plant pathogenic microbes, plant parasitic nematodes, and weeds. Additionally, chitin, which is found in the shell of crustaceans, impacted the incident of root-knot nematodes in cut flowers. Dimethyl disulfide (DMDS) is an organic compound has been shown to be a successful soil fumigant for managing soilborne pests and pathogens. However, DMDS has a strong odor which has limited its adoption by growers. ARS scientists were able to show that DMDS paired with oak residue biochar reduced the detection of DMDS and maintained its nematicide activity. The research conducted provides growers, especially organic growers, more tools for combating soilborne-limiting factors.
2. Optimization of anaerobic soil disinfestation. Anaerobic soil disinfestation (ASD) is a biologically based preplant technique, which has been shown to be as effective as methyl bromide for managing weeds and soilborne plant pests and pathogens. ASD consists of amending the soils with a carbon source, feed-grade molasses in Florida, and the soil is tarped and then watered. The environment under the tarp becomes anaerobic and the anaerobic microbes produce antimicrobial compounds, which manage soilborne pathogens, pests, and weeds. ARS scientists from Fort Pierce, Florida surveyed growers to discover what could increase grower adoption of ASD. One of their top concerns was the availability and cost of feed-grade molasses. Thus, these ARS researchers collected waste products, such as algae, common weeds, cover crops, and, food industry byproducts to determine if these products could be an alternative for molasses. Various cover crops, such as cowpea and sunn hemp, have shown to potential to be an alternative carbon sources for molasses or at least reduce the amount of molasses used in ASD application. Additionally, ARS scientists have developed a product from the components of ASD, which when added to a half rate of molasses created an anaerobic environment longer than the traditional application of ASD. The overall impact of this research could reduce the cost of ASD application and encourage grower adoption.
3. Utilizing grafting as a technique to mitigate the impact of soil-borne plant pathogens and nematodes on crop yield. Plant geneticists discovered plant pathogen and root-knot nematode resistance genes. However, fruits produced from resistant plants are often smaller and less succulent than those from susceptible plants. Grafting consumer desirable scions, like ‘heirloom’ varieties, which are rich in color and taste but disease prone, onto resistant rootstock offers a solution. ARS researchers from Fort Pierce, Florida identified 18 nematode and plant pathogen resistant tomato rootstocks. These rootstocks were grafted on heirloom scions. Yields from the grafted plants performed very well, however in two commercial field experiments the resistance to nematodes broke down. Further experiments were conducted to determine factors that could contribute to the resistance breakdown. It was discovered that when multiple species of root-knot nematodes were co-inoculated galling increased. In another study it was observed that resistance to Phytophthora capsica broke down as grafted bell peppers were exposed to salinity stress. Salinity stress is of great concern for vegetable growers on the coasts of Florida as salinity levels have increased in ground water. The overall impact of this accomplishment highlights that vegetable grafting, while not foolproof, provides another tool for vegetable growers to limit the impact of soilborne pathogens and parasitic nematodes.
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