Organic amendments have been widely used for management of plant-parasitic nematodes. Relatively rapid declines in nematode population levels may occur when decomposing materials release toxic compounds, while longer-term effects might include increases in nematode antagonists. Improved crop nutrition and plant growth following amendment use may lead to tolerance of plant-parasitic nematodes. Results depend on a great variety of factors such as material used, processing/composting of material, application rate, test arena, crop rotation and agronomic practices, soil type, climate, and other environmental factors. Reasons for variable performance and interpretation of results from amendment studies are discussed. Case studies of amendments for nematode management are reviewed from Florida, where composts and crop residues are the most frequently used amendments. Plant growth was often improved by amendment application, free-living nematodes (especially bacterivores) were often stimulated, but suppression of plant-parasitic nematodes was inconsistent. Amendments were generally not as effective as soil fumigation with methyl bromide for managing root-knot nematodes (Meloidogyne spp.), and often population levels or galling of root-knot nematodes in amended plots did not differ from those in non-amended control plots. While amendments may improve plant growth and stimulate soil food webs, additional study and testing are needed before they could be used reliably for management of plant-parasitic nematodes under Florida conditions.
biological control; compost; free-living nematodes; mulch; organic agriculture; pest management; soil food web; sustainable agriculture
Conservation biological control is the modification of the environment or existing practices to protect and enhance antagonistic organisms to reduce damage from pests. This approach to biological control has received insufficient attention compared with inundative applications of microbial antagonists to control nematodes. This review provides examples of how production practices can enhance or diminish biological control of plant-parasitic nematodes and other soilborne pests. Antagonists of nematodes can be enhanced by providing supplementary food sources such as occurs when organic amendments are applied to soil. However, some organic amendments (e.g., manures and plants containing allelopathic compounds) can also be detrimental to nematode antagonists. Plant species and genotype can strongly influence the outcome of biological control. For instance, the susceptibility of the plant to the nematode can determine the effectiveness of control; good hosts will require greater levels of suppression than poor hosts. Plant genotype can also influence the degree of rhizosphere colonization and antibiotic production by antagonists, as well the expression of induced resistance by plants. Production practices such as crop rotation, fallow periods, tillage, and pesticide applications can directly disrupt populations of antagonistic organisms. These practices can also indirectly affect antagonists by reducing their primary nematode host. One of the challenges of conservation biological control is that practices intended to protect or enhance suppression of nematodes may not be effective in all field sites because they are dependent on indigenous antagonists. Ultimately, indicators will need to be identified, such as the presence of particular antagonists, which can guide decisions on where it is practical to use conservation biological control. Antagonists can also be applied to field sites in conjunction with conservation practices to improve the consistency, efficacy, and duration of biological control. In future research, greater use should be made of bioassays that measure nematode suppression because changes in abundance of particular antagonists may not affect biological control of plant parasites.
antagonists; biological control; crop rotation; farming practices; organic amendments; pesticides; plant genotype; tillage
Brassicas have been used frequently for biofumigation, a pest-management strategy based on the release of biocidal volatiles during decomposition of soil-incorporated tissue. However, the role of such volatiles in control of plant-parasitic nematodes is unclear. The goal of this study was to determine the direct localized and indirect volatile effects of amending soil with broccoli tissue on root-knot nematode populations. Meloidogyne incognita-infested soil in 50-cm-long tubes was amended with broccoli tissue, which was mixed throughout the tube or concentrated in a 10-cm layer. After three weeks at 28°C, M. incognita populations in the amended tubes were 57 to 80% smaller than in non-amended tubes. Mixing broccoli throughout the tubes reduced M. incognita more than concentrating broccoli in a 10-cm layer. Amending a 10-cm layer reduced M. incognita in the non-amended layers of those tubes by 31 to 71%, probably due to a nematicidal effect of released volatiles. However, the localized direct effect was much stronger than the indirect effect of volatiles. The strong direct effect may have resulted from the release of non-volatile nematicidal compounds. Therefore, when using biofumigation with broccoli to control M. incognita, the tissue should be thoroughly and evenly mixed through the soil layer(s) where the target nematodes occur. Effects on saprophytic nematodes were the reverse. Amended soil layers had much greater numbers of saprophytic nematodes than non-amended layers, and there was no indirect effect of amendments on saprophytic nematodes in adjacent non-amended layers.
amendment; biofumigation; broccoli; Brassica oleracea; management; Meloidogyne incognita; root-knot nematode; soil
The effects of perennial peanut (Arachis glabrata) hay, an aged yard-waste compost (mainly woodchips), and a control treatment without amendment were determined on two population levels of root-knot (Melaidogyne arenaria) nematode over three consecutive years in field microplots. Okra (Hibiscus esculentus, susceptible to the root-knot nematode) and a rye (Secale cereale) cover crop (poor nematode host) were used in the summer and winter seasons, respectively. The organic amendment treatments affected plant growth parameters. In the first year, okra yields were greatest in peanut-amended plots. Yield differences with amendment treatment diminished in the second and third years. Okra plant height, total fruit weight, and fruit number were greater with the lower population level of the root-knot nematode. Residual levels of nutrients in soil were greater where root-knot nematode levels and damage were higher and plant growth was poor. Nutrient levels affected the growth of a subsequent rye cover crop.
compost; Hibiscus esculentus; Meloidogyne arenaria; nematode; organic amendments; pest management; root-knot nematode; sustainable agriculture
Previous laboratory research demonstrated that N-Viro Soil (NVS), an alkaline-stabilized municipal biosolid, suppressed plant-parasitic nematodes. This study continued to explore the use of NVS as a nematode management tool specifically addressing factors that could influence its use. N-Viro Soil from different locations, the components of NVS (de-watered biosolids and fly ash admixtures), and sterilized NVS were applied to sand microcosms to determine effects on nematode survival sand solution pH and ammonia concentrations. This study confirmed the previous finding that an important mechanism of Heterodera glycines suppression by NVS was the generation of alkaline soil conditions. Only the fly ash admixture that resulted in an increase in pH to 10.0 suppressed H. glycines to the same level as NVS. Alkaline-stabilization of biosolids was necessary to achieve nematode suppression. Biosolids applied at rates <3% dry w/w did not suppress H. glycines to the same level as equivalent amounts of NVS. Sand solution pH levels after biosolid application, regardless of rate, were approximately 8.5 whereas 1% and 4% w/w NVS amendment resulted in pH levels of 10.3 and 11.6, respectively. NVS from different processing facilities were all effective in suppressing H. glycines. The NVS source that produced the highest concentration of ammonia did not reduce H. glycines survival to the same level as those sources generating pH levels above 10.1. Microbes associated with NVS appeared not to be responsible for the nematode suppressiveness of the amendment; there was no difference in nematode suppression between autoclaved and nonautoclaved NVS. The role that ammonia plays in the suppression of H. glycines by NVS is still unclear.
ammonia; biosolid; Heterodera glycines; Meloidogyne incognita; nematodes; pH
Preventive and/or manipulative practices will be needed to maintain soil's biological, physiochemical, nutritional, and structural health in natural, managed, and disturbed ecosystems as a foundation for food security and global ecosystem sustainability. While there is a substantial body of interdisciplinary science on understanding function and structure of soil ecosystems, key gaps must be bridged in assessing integrated agro-biological, ecological, economical, and environmental efficiency of soil manipulation practices in time and space across ecosystems. This presentation discusses the application of a fertilizer use efficiency (FUE) model for assessing agronomic, economic, ecological, environmental, and nematode (pest) management efficiency of soil amendments. FUE is defined as increase in host productivity and/or decrease in plant-parasitic nematode population density in response to a given fertilizer treatment. Using the effects of nutrient amendment on Heterodera glycines population density and normalized difference vegetative index (indicator of physiological activities) of a soybean cultivar ‘CX 252’, how the FUE model recognizes variable responses and separates nutrient deficiency and toxicity from nematode parasitism as well as suitability of treatments designed to achieve desired biological and physiochemical soil health conditions is demonstrated. As part of bridging gaps between agricultural and ecological approaches to integrated understanding and management of soil health, modifications of the FUE model for analyzing the relationships amongst nematode community structure, soil parameters (eg. pH, nutrients, %OM), and plant response to soil amendment is discussed.
fertilizer use efficiency model; normalized difference vegetative index; nutrient amendment; soil amendments; soil degradation; soybeans; soybean cyst nematode
Population densities of nematodes in field soil without plants were monitored for 10 months following application of organic amendments to pots in a greenhouse. The four treatments consisted of three different kinds of organic amendments: homogeneous crop residues of maize (Zea mays, C:N = 48.0:1), Texas panicum (Panicum texanum, C:N = 32.9:1), or velvetbean (Mucuna pruriens, C:N = 18.6:1), plus a control without any amendment. Plant-parasitic nematodes declined in all treatments due to absence of a food source. Bacterivore numbers increased following amendment application and remained greater than initial population levels until 4 months after application. Fungivore numbers were higher than initial levels until 6 months after amendment application and did not decline below the initial numbers during the course of the experiment. On several sampling dates, the bacterivorous genera Cervidellus and Eucephalobus were most abundant in pots with maize residues. Among the fungivores, Aphelenchoides numbers early in the experiment were greatest in pots amended with velvetbean, whereas numbers of Aphelenchus, Nothotylenchus, and Tylenchidae (mainly Filenchus) were greatest during the latter half of the experiment following the maize amendment. Omnivorous nematodes, particularly Eudorylaimus, showed two peaks in abundance during the course of the experiment. Results provided some evidence that population levels of some genera of bacterivores and fungivores may be affected by specific organic amendments.
bacterivores; fungivores; nematode community; omnivores; plant parasitics; predators; soil ecology; trophic groups
Nonchemical methods and strategies for nematode management including cultural methods and engineered measures have been recommended as an alternative to methyl bromide (a major soil fumigant), due to its role in the depletion of the ozone layer. Hence, an international agreement has recently been reached calling for its reduced consumption and complete phasing out. This present research evaluates the potential of Ecologic, a biological, marine shell meal chitin material, as a soil amendment management agent for root knot nematode, Meloidogyne incognita, control, and its effect on the growth of Floradel tomato plant, Lycopersicon esculentum. To accomplish this goal, studies were conducted during which, experimental pots were set up in greenhouse environments using sterilized soil inoculated with 5,000 root-knot eggs per 1500 g soil. There were 4 treatments and 5 replications. Treatments were: No chitin; 50 g chitin; 100 g chitin; and 200 g chitin. A two-week wait period following Ecologic amendment preceded Floradel tomato planting to allow breakdown of the chitin material into the soil. Fresh and dry weights of shoot and root materials were taken as growth end-points. A statistically significant difference (p ≤ 0.05) was obtained with regard to the growth rate of L. esculentum at 100 g chitin treatment compared to the control with no chitin. Mean fresh weights of Floradel tomato were 78.0 ± 22.3g, 81.0 ± 20.3g, 109.0 ± 25.4g and 102.0 ± 33.3g at 0, 50, 100 and 200g chitin, respectively. The analysis of root knot nematode concentrations indicated a substantial effect on reproduction rate associated with chitin amendment. Study results showed a significant decrease in both root knot nematode eggs and juveniles (J2) at 100g and 200g Ecologic chitin levels, however, an increase in nematode concentrations was recorded at the 50g Ecologic chitin level (p ≤ 0.05). The mean amounts of J2 population, as expressed per 1500cm3 soil, were 49,933 ± 38,819, 86,050 ± 25248, 103 ± 133 and 103 ± 133 for 0, 50, 100 and 200g chitin, respectively. Similarly, the mean numbers of root knot nematode eggs (per 1500cm3 of soil) were 40,759 ± 36,712, 66,048 ± 39,730, 9,904 ± 16,591 and 9,257 ± 17,204. Root gall rating was also significantly lower (p ≤ 0.05) at the 100g and 200g chitin levels compared to the control. Percent gall ratings were 3.3 ± 1.0%, 3.2 ± 1.0%, 1.0 ± 0.5%, and 1.0% ± 0.6% for amendment levels of 0, 50, 100, and 200g chitin, respectively.
Ecologic chitin; root knot nematode; tomato plant; agricultural management
The effects of soil solarization and ammonium bicarbonate or ammonium sulfate against plant-parasitic nematodes on yellow squash (Cucurbita pepo) and on vinca (Catharanthus roseus) were evaluated at two sites. Solarization for 3 weeks in the spring suppressed population levels of Belonolaimus longicaudatus, Criconemella spp., and Dolichodorus heterocephalus throughout the growing season on both crops at both sites. Levels of Meloidogyne incognita were suppressed initially, but population densities increased by the end of the crop in several cases. In one site, numbers of Paratrichodorus minor resurged following solarization to levels that were greater than those present in unsolarized control plots. The effect of solarization was not enhanced by combination with ammonium amendments, but, in one site, application of ammonium bicarbonate or ammonium sulfate resulted in lower numbers of B. longicaudatus than in the unamended control. Additional research and improved efficacy of candidate amendments are required before they can be successfully integrated with solarization for nematode management. Efficacy of solarization against plant-parasitic nematodes was achieved despite a relatively short (3 weeks) solarization period.
ammonium bicarbonate; ammonium sulfate; Belonolaimus longicaudatus; Catharanthus roseus; Cucurbita pepo; Dolichodorus heterocephalus; integrated pest management; Meloidogyne incognita; nematode; Paratrichodorus minor; squash; sustainable agriculture; vinca
Two greenhouse experiments were conducted to examine the effect of Crotalaria juncea amendment on Meloidogyne incognita population levels and growth of yellow squash (Cucurbita pepo). In the first experiment, four soils with a long history of receiving yard waste compost (YWC+), no-yard-waste compost (YWC-), conventional tillage, or no-tillage treatments were used; in the second experiment, only one recently cultivated soil was used. Half of the amount of each soil received air-dried residues of C. juncea as amendment before planting squash, whereas the other half did not. Crotalaria juncea amendment increased squash shoot and root weights in all soils tested, except in YWC+ soil where the organic matter content was high without the amendment. The amendment suppressed the numbers of M. incognita if the inoculum level was low, and when the soil contained relatively abundant nematode-antagonistic fungi. Microwaved soil resulted in greater numbers of M. incognita and free-living nematodes than frozen or untreated soil, indicating nematode-antagonistic microorganisms played a role in nematode suppression. The effects of C. juncea amendment on nutrient cycling were complex. Amendment with C. juncea increased the abundance of free-living nematodes and Harposporium anguillulae, a fungus antagonistic to them in the second experiment but not in the first experiment. Soil histories, especially long-term yard waste compost treatments that increased soil organic matter, can affect the performance of C. juncea amendment.
free-living nematode; nematode-trapping fungi; organic amendments; root-knot nematode; soil ecosystem; soil nutrient; sunn hemp; tillage
In a repeated greenhouse experiment, organic soil amendments were screened for effects on population density of soybean cyst nematode (SCN), Heterodera glycines, and soybean growth. Ten amendments at various rates were tested: fresh plant material of field pennycress, marigold, spring camelina, and Cuphea; condensed distiller’s solubles (CDS), ash of combusted CDS, ash of combusted turkey manure (TMA), marigold powder, canola meal, and pennycress seed powder. Soybeans were grown for 70 d in field soil with amendments and SCN eggs incorporated at planting. At 40 d after planting (DAP), many amendments reduced SCN egg population density, but some also reduced plant height. Cuphea plant at application rate of 2.9% (amendment:soil, w:w, same below), marigold plant at 2.9%, pennycress seed powder at 0.5%, canola meal at 1%, and CDS at 4.3% were effective against SCN with population reductions of 35.2%, 46.6%, 46.7%, 73.2%, and 73.3% compared with control, respectively. For Experiment 1 at 70 DAP, canola meal at 1% and pennycress seed powder at 0.5% reduced SCN population density 70% and 54%, respectively. CDS at 4.3%, ash of CDS at 0.2%, and TMA at 1% increased dry plant mass whereas CDS at 4.3% and pennycress seed powder at 0.1% reduced plant height. For Experiment 2 at 70 DAP, amendments did not affect SCN population nor plant growth. In summary, some amendments were effective for SCN management, but phytoxicity was a concern.
Calendula; Camelina sativa; canola meal; condensed distiller’s solubles; Cuphea; field pennycress; Glycine max; green manure; Heterodera glycines; management; marigold; organic fertilizer; organic soil amendment; soybean; soybean cyst nematode; spring camelina; Thlaspi arvense; turkey manure ash
Effects of winter cover crop management on nematode densities associated with a subsequent corn (Zea mays) crop were examined in five sites in north Florida. Two sites had received winter cover crops of lupine (Lupinus angustifolius), and one site each had rye (Secale cereale), hairy vetch (Vicia villosa), and crimson clover (Trifolium incarnatum). In each site, five different management regimes were compared: 1) conventional tillage after the cover crop was removed for forage; 2) conventional tillage with the cover crop retained as green manure; 3) no-till with the cover crop mowed and used as a mulch; 4) no-till with the cover crop removed as forage; and 5) fallow. Sites were sampled at corn planting and harvest for estimates of initial (Pi) and final (Pf) nematode population densities, respectively. Whether the cover crop was removed as forage or retained as green manure or mulch had no effect (P > 0.10) on population densities of any plant-parasitic nematode before or after corn at any site. Differences between conventional-till and no-till treatments were significant (P ≤ 0.10) only in one experiment for Paratrichodorus minor and two experiments for Pratylenchus spp. Compared with other treatments, fallow reduced (P ≤ 0.05) Pi of P. minor in two of three cases and Pf of Meloidogyne incognita in one of five sites, but enhanced soil Pf of Pratylenchus spp. in three of five sites. Tillage practices and management of cover crop residues had little consistent effect on nematodes, and these practices should be considered based on agronomic benefits rather than for nematode management.
corn; Criconemella spp.; cover crop; cropping system; green manure; Meloidogyne incognita; nematode; organic amendment; Paratrichodorus minor; Pratylenchus spp.; sustainable agriculture; tillage; Zea mays
The effects of chicken litter on Meloidogyne arenaria in tomato plants cv. Rutgers were determined in the greenhouse. Tomato seedlings were transplanted into a sandy soil amended with five rates of chicken litter and inoculated with 2,000 M. arenaria eggs. After 10 days, total numbers of nematodes in the roots decreased with increasing rates of chicken litter. After 46 days, egg numbers also decreased with increasing litter rates. In another experiment, soil was amended with two litter types, N-P-K fertilizer, and the two primary constituents of chicken litter (manure and pine-shaving bedding). After 10 days, numbers of nematodes in roots were smaller in chicken-excrement treatments as compared to nonexcrement treatments. At 46 days, there were fewer nematode eggs in chicken-excrement treatments compared to nonexcrement treatments. Egg numbers also were smaller for fertilizer and pine-shaving amendments as compared to nonamended controls. Chicken litter and manure amendments suppressed plant growth by 10 days after inoculation but enhanced root weights at 46 days after inoculation. Amendment of soil with chicken litter suppressed M. arenaria and may provide practical control of root-knot nematodes as part of an integrated management system.
amendment; biological control; chicken litter; Lycopersicon esculentum; Meloidogyne arenaria; nematode; penetration; root-knot nematode; tomato
A 7-year study located in Prince Edward Island, Canada, examined the influence of compost and manure on crop yield and nematode populations. The compost used in this study consisted of cull waste potatoes, sawdust, and beef manure in a 3:3:1 ratio, respectively. No plant-parasitic nematodes were detected in samples collected from windrow compost piles at 5- and 30-cm depths prior to application on field plots. Low population densities of bacterial-feeding nematodes were recovered from compost windrows at the 5-cm depth. Field plots of potato (Solanum tuberosum cv. Kennebec) received compost applied at 16 metric tonnes per hectare, or beef manure applied at 12 metric tonnes per hectare. An adjacent trial with barley (Hordeum vulgare cv. Mic Mac) received only the compost treatment. In both trials the experimental design was a complete randomized block with four replicates. Data averaged over seven growing seasons indicated that population levels of root-lesion nematodes (primarily Pratylenchus penetrans) were higher in root-zone soil in potato plots treated with either compost or manure compared to the untreated control plots. The soil amendments did not affect root-knot nematode (Meloidogyne hapla) population densities in the potato plots, but clover-cyst nematodes (Heterodera trifolii) were more numerous in the root-zone soils of barley treated with compost compared to the untreated plots. Numbers of bacterial-feeding nematodes (primarily Diplogaster lheritieri) were greater in soil in potato plots treated with manure and in soil around barley roots than in untreated plots. Total yields of potato tubers averaged over seven growing seasons increased by 27% in the plots treated with either compost or manure. Grain yields of barley also were increased by 12% when compost was applied. These results indicated that organic amendments increased crop yields, but the impacts on different nematode species varied and usually increased soil population levels.
bacterial-feeding nematodes; barley; beef manure; clover cyst nematode; compost; cull potato; Diplogaster lheritieri; Heterodera trifolii; potato; root-knot nematode; root-lesion nematode; sawdust
N-Viro Soil (NVS) is an alkaline-stabilized municipal biosolid that has been shown to lower population densities and reduce egg hatch of Heterodera glycines and other plant-parasitic nematodes; but the mechanism(s) of nematode suppression of this soil amendment are unknown. This study sought to identify NVS-mediated changes in soil chemical properties and their impact upon H. glycines and Meloidogyne incognita mortality. N-Viro Soil was applied to sand in laboratory assays at 0.5%, 1.0%, 2.0%, and 3.0% dry w/w with a nonamended treatment as a control. Nematode mortality and changes in sand-assay chemical properties were determined 24 hours after incubation. Calculated lethal concentration (LC90) values were 1.4% w/w NVS for second-stage juveniles of both nematode species and 2.6 and >3.0% w/w NVS for eggs of M. incognita and H. glycines, respectively. Increasing rates of NVS were strongly correlated (r² = 0.84) with higher sand solution pH levels. Sand solution pH levels and, to a lesser extent, the production of ammonia appeared to be the inorganic chemical-mediated factors responsible for killing plant-parasitic nematodes following amendment with NVS.
amendment; ammonia; biosolid; Heterodera glycines; Meloidogyne incognita; nematodes; pH
The organisms of the soil food web, dependent on resources from plants or on amendment from other sources, respond characteristically to enrichment of their environment by organic matter. Primary consumers of the incoming substrate, including bacteria, fungi, plant-feeding nematodes, annelids, and some microarthropods, are entry-level indicators of enrichment. However, the quantification of abundance and biomass of this diverse group, as an indicator of resource status, requires a plethora of extraction and assessment techniques. Soluble organic compounds are absorbed by bacteria and fungi, while fungi also degrade more recalcitrant sources. These organisms are potential indicators of the nature of incoming substrate, but current methods of biomass determination do not reliably indicate their community composition. Guilds of nematodes that feed on bacteria (e.g., Rhabditidae, Panagrolaimidae) and fungi (e.g., Aphelenchidae, Aphelenchoididae) are responsive to changes in abundance of their food. Through direct herbivory, plant-feeding nematodes (e.g., many species of Tylenchina) also contribute to food web resources. Thus, analysis of the nematode community of a single sample provides indication of carbon flow through an important herbivore channel and through channels mediated by bacteria and fungi. Some nematode guilds are more responsive than others to resource enrichment. Generally, those bacterivores with short lifecycles and high reproductive potential (e.g., Rhabditidae) most closely mirror the bloom of bacteria or respond most rapidly to active plant growth. The feeding habits of some groups remain unclear. For example, nematodes of the Tylenchidae may constitute 30% or more of the individuals in a soil sample; further study is necessary to determine which resource channels they portray and the appropriate level of taxonomic resolution for this group. A graphic representation of the relative biomass of bacterivorous, fungivorous, and herbivorous nematodes provides a useful tool for assessing the importance of the bacterial, fungal, and plant resource channels in an extant food web.
enrichment index; enrichment profile; faunal analysis; soil food web; structure index
Interpretation of nematode community indices requires a reference to a relatively undisturbed community. Maturity and trophic diversity index values were compared for five pairs of certified organically and conventionally managed soils in the Piedmont region of North Carolina. Available nitrogen (nitrate, ammonium) was estimated at various lag periods relative to times of sampling for nematode communities to determine the strength of correlative relationship between nematode communities and nitrogen availability. Soils were sampled six times yearly in 1993 and 1994 to determine the best time of year to sample. Maturity values for plant parasites were greater in organically than conventionally managed soils, and differences between management systems were greater in fall than spring months. However, other maturity and diversity indices did not differ between the two management practices. Differences in crop species grown in the two systems accounted for most differences observed in the community of plant-parasitic nematodes. Indices of free-living nematodes were correlated negatively with concentrations of ammonium, whereas indices of plant-parasitic nematodes were correlated positively with concentrations of nitrate. Due to the similarity of index values between the two systems, organically managed soils are not suitable reference sites for monitoring and assessing the biological aspects of soil quality for annually harvested crops.
community structure; conventional farming; ecology; maturity index; monitoring; nematode; ordination; organic farming; reference sites; trophic diversity
Effect of sunn hemp (Crotalaria juncea) hay amendment on nematode community structure in the soil surrounding roots of yellow squash (Cucurbita pepo) infected with root-knot nematodes was examined in two greenhouse experiments. Soils were from field plots treated long-term (LT) with yard-waste compost or no yard-waste compost in LT experiment, and from a short-term (ST) agricultural site in ST experiment. Soils collected were either amended or not amended with C. juncea hay. Nematode communities were examined 2 months after squash was inoculated with Meloidogyne incognita. Amendment increased (P < 0.05) omnivorous nematodes in both experiments but increased only bacterivorous nematodes in ST experiment (P < 0.05), where the soil had relatively low organic matter (<2%). This effect of C. juncea amendment did not occur in LT experiment, in which bacterivores were already abundant. Fungivorous nematodes were not increased by C. juncea amendment in either experiment, but predatory nematodes were increased when present. Although most nematode faunal indices, including enrichment index, structure index, and channel index, were not affected by C. juncea amendment, structure index values were affected by previous soil organic matter content. Results illustrate the importance of considering soil history (organic matter, nutrient level, free-living nematode number) in anticipating changes following amendment with C. juncea hay.
community structure indices; Cucurbita pepo; Meloidogyne incognita; organic amendments; squash; sunn hemp
In an outside pot experiment, dry pig manure processed on pine sawdust litter and fermented for seven days by house fly larvae (fermented manure), and pine sawdust applied alone, and in combination with a spring application of inorganic nitrogen fertilizer were used to determine their effects on plant parasitic and free-living soil nematodes on sugar beets (cv. Antek). Non amended soil was used as a control. All treatments with fermented pig manure and sawdust with nitrogen fertilizer decreased number of plant parasitic nematodes and also root-fungal feeding nematodes compared to the untreated control. Sawdust applied alone had no effect on plant parasitic and root-fungal feeding nematode suppression. Free-living nematodes which were mainly bacteriovores and fungivores were significantly more abundant in soil amended with fermented pig manure, while the sawdust had no effect on these nematodes. The effect of all tested treatments on omnivores-predators was rather random, and in general, the number of these nematodes decreased after soil amendment applications compared to the untreated control.
fermented animal manure; nematode trophic groups; nitrogen amendments; phytoparasitic nematodes; sawdust
Chitin was used as soil amendment in fiberglass field microplots, alone or with one or a combination of two to three species of Hirsutella rhossiliensis, Paecilomyces marquandii, Verticillium chlamydosporium, Bacillus thuringiensis, and Streptomyces costaricanus. Sudangrass and rapeseed were planted as cover crops and incorporated into soil as green manure amendments. Chitin amendment alone increased the marketable yield of lettuce in 1995 and reduced root-galling ratings and the reproduction of Meloidogyne hapla in both 1995 and 1996. Green manure amendments of sudangrass and rapeseed increased total and marketable yields of lettuce, and decreased root-galling ratings and the reproduction of M. hapla in 1996. Hirsutella rhossiliensis in combination with chitin increased total yield of lettuce over the chitin amendment alone in 1995. The combination of B. thuringiensis, S. costaricanus, and chitin either with or without P. marquandii increased total yield of lettuce over the chitin amendment alone in 1996. In most cases, however, the nematode-antagonistic organisms did not improve lettuce yield or further suppression of M. hapla compared to the chitin amendment alone. The introduced fungi were recoverable from the infested soil. The rifampicin-resistant mutant of B. thuringiensis was not isolated at the end of the season.
Bacillus thuringiensis; biological control; chitin amendment; cover crop; green manure; Hirsutella rhossiliensis; Lactuca sativa; Meloidogyne hapla; nematode; northern root-knot nematode; Paecilomyces marquandii; Streptomyces costaricanus; Verticillium chlamydosporium
1,3-Dichloropropene (1,3-D) is a likely alternative soil fumigant for methyl bromide. The objective was to determine root-knot nematode, Meloidogyne incognita, survival in microplots after exposure to 1,3-D for various periods of time in soil that have previously been amended with compost. The treatments were 1,3-D applied broadcast at 112 liters/ha and untreated controls in both compost-amended and unamended soil. Soil samples were collected from each microplot at 6, 24, 48, 72, and 96 hours after fumigation at three depths (0-15, 15-30, and 30-45 cm). One week after fumigation, six tomato seedlings were transplanted into each microplot and root galling was recorded 6 weeks later. Plants grown in fumigated compost-amended soil had more galls than plants from fumigated unamended soil at P ≤ 0.1. Gall indices from roots in fumigated soil amended with compost were not different from nonfumigated controls. Based on soil bioassays, the number of galls decreased with increasing time after fumigation in both compost-amended and unamended soil at 0-to-15 and 15-to-30 cm depths, but not at 30 to 45 cm deep. Higher soil water content due to the elevated levels of organic matter in the soil at these depths may have interfered with 1,3-D movement, thus reducing its efficacy.
compost-amended soil; deep sand soil; 1,3-dichloropropene; fumigation; Lycopersicon esculentum; Meloidogyne incognita; nematicide; nematode; root-knot nematode; tomato
Naturally occurring disease-suppressive soils have been documented in a variety of cropping systems, and in many instances the biological attributes contributing to suppressiveness have been identified. While these studies have often yielded an understanding of operative mechanisms leading to the suppressive state, significant difficulty has been realized in the transfer of this knowledge into achieving effective field-level disease control. Early efforts focused on the inundative application of individual or mixtures of microbial strains recovered from these systems and known to function in specific soil suppressiveness. However, the introduction of biological agents into non-native soil ecosystems typically yielded inconsistent levels of disease control. Of late, greater emphasis has been placed on manipulation of the cropping system to manage resident beneficial rhizosphere microorganisms as a means to suppress soilborne plant pathogens. One such strategy is the cropping of specific plant species or genotypes or the application of soil amendments with the goal of selectively enhancing disease-suppressive rhizobacteria communities. This approach has been utilized in a system attempting to employ biological elements resident to orchard ecosystems as a means to control the biologically complex phenomenon termed apple replant disease. Cropping of wheat in apple orchard soils prior to re-planting the site to apple provided control of the fungal pathogen Rhizoctonia solani AG-5. Disease control was elicited in a wheat cultivar-specific manner and functioned through transformation of the fluorescent pseudomonad population colonizing the rhizosphere of apple. Wheat cultivars that induced disease suppression enhanced populations of specific fluorescent pseudomonad genotypes with antagonistic activity toward R. solani AG-5, but cultivars that did not elicit a disease-suppressive soil did not modify the antagonistic capacity of this bacterial community. Alternatively, brassicaceae seed meal amendments were utilized to develop soil suppressiveness toward R. solani. Suppression of Rhizoctonia root rot in response to seed meal amendment required the activity of the resident soil microbiota and was associated with elevated populations of Streptomyces spp. recovered from the apple rhizosphere. Application of individual Streptomyces spp. to soil systems provided control of R. solani to a level and in a manner equivalent to that obtained with the seed meal amendment. These and other examples suggest that management of resident plant-beneficial rhizobacteria may be a viable method for control of specific soilborne plant pathogens.
suppressive soils; biological control; replant disease; rhizobacteria
Effectiveness of castor (Ricinus communis) and velvetbean (Mucuna deeringiana) amendments was tested for suppression of the root-knot nematode (Meloidogyne arenaria) and growth of okra (Hibiscus esculentus) in three greenhouse experiments. Regression analysis was used to relate nematode population data or plant growth responses to various rates (0, 1, 2, 4, or 8 g/560 cm³ soil pot) of each amendment in separate experiments. In general, plant growth parameters responded positively to the amendment rate until a level of about 4 g to 5 g of velvetbean or castor amendment/pot. Similar trends were observed for nematode galls, egg masses, and second-stage juveniles extracted from root systems. In most circumstances, quadratic equations best expressed the relationships between plant or nematode parameters and rates of velvetbean or castor amendment, leading to the assumption that a best rate of the amendment for plant growth or nematode suppression can be predicted. In a third experiment, in which both amendments were compared directly, velvetbean amendment was more efficient than castor in suppressing nematodes as well as in improving plant growth.
Hibiscus esculentus; Meloidogyne arenaria; Mucuna deeringiana; nematode; nematode management; okra; Ricinus communis; root-knot nematode
Of the 56 species and 43 genera of Asteraceae tested, 9 were highly resistant or immune to Meloidogyne incognita and did not form root galls. Twenty-six species and six cultivars had 25% or fewer roots galled and were considered moderately resistant to M. incognita. Pre-planting Cosmos bipinnatus (F190), Gaillardia pulchella, Tagetes erecta, Tithonia diversifolia, or Zinnia elegans (F645) reduced root galling and M. incognita J2 in and around Ipomoea reptans. Amendment of soils with roots, stems, or leaves of G. pulchella was effective in controlling M. incognita on I. reptans. Tissue extracts of G. pulchella were lethal to various plant-parasitic nematodes but were innocuous to free-living nematodes. Root exudates of G. pulchella were lethal to J2 of M. incognita and were inhibitory to the hatch of eggs at the concentration of 250 ppm or higher. Gaillardia pulchella could be used to manage M. incognita as a rotation crop, a co-planted crop, or a soil amendment for control of root-knot nematode.
antagonistic plants; Asteraceous plants; Ipomoea repans; root exudates; rotation; soil amendment; tissue extracts
Experiments were conducted to determine whether the addition of organic matter to soil increased numbers of bacterivorous nematodes and parasitic activity of the nematophagous fungus Hirsutella rhossiliensis. In a peach orchard on loamy sand, parasitism of the plant-parasitic nematode Criconemella xenoplax by H. rhossiliensis was slightly suppressed and numbers of C. xenoplax were not affected by addition of 73 metric tons of composted chicken manure/ha. In the laboratory, numbers of bacterivorous nematodes (especially Acrobeloides spp.) and fungivorous nematodes increased but parasitism of nematodes by H. rhossiliensis usually decreased with addition of wheat straw or composted cow manure to a loamy sand naturally infested with H. rhossiliensis. These results do not support the hypothesis that organic amendments will enhance parasitism of nematodes by H. rhossiliensis.
bacterivorous nematode; biocontrol; biological control; Criconemella xenoplax; density-dependent parasitism; fungivorous nematode; Hirsutella rhossiliensis; nematode; nematophagous fungus; organic amendment