Dan O. Chellemi

Adaptation of Soil Solarization to the Integrated Management of Soilborne Pests of Tomato Under Humid Conditions

ABSTRACT Soil solarization was shown to be cost effective, compatible with other pest management tactics, readily integrated into standard production systems, and a valid alternative to preplant fumigation with methyl bromide under the tested conditions. Solarization using clear, photoselective, or gas-impermeable plastic was evaluated in combination with metham sodium, 1,3-dichloropropene + chloropicrin, methyl bromide + chloropicrin, pebulate, or cabbage residue. Strip solarization, applied to 20-cm-high, 0.9-m-wide beds, was conducted to achieve compatibility with standard production practices and resulted in soil temperatures 2 to 4 degrees C above those temperatures resulting when using conventional flatbed solarization. Soil temperatures were 1 to 2 degrees C higher at the edges of the raised beds, eliminating any border effects associated with solarization. Following a 40- to 55-day solarization period, the plastic was painted white and used as a production mulch for a subsequent tomato crop. The incidence of Southern blight and the density of Paratrichodorus minor and Criconemella spp. were lower (P < 0.05) in solarized plots. No differences (P < 0.05) in the incidence of Fusarium wilt and the density of nutsedge and Helicotylenchus spp. were observed between plots receiving solarization and plots fumigated with a mixture of methyl bromide + chloropicrin. The severity of root galling was lower (P < 0.05) when soil solarization was combined with 1,3-dichloropropene + chloropicrin (16.2 + 3.4 g/m(2)) and a gas-impermeable film. The incidence of bacterial wilt was not affected by soil treatments. Marketable yields in plots using various combinations of soil solarization and other tactics were similar (P < 0.05) to yields obtained in plots fumigated with methyl bromide + chloropicrin. The results were validated in several large scale field experiments conducted by commercial growers.

Effects of soil solarization and fumigation on survival of soilborne pathogens of tomato in Northern Florida

The effects of soil solarization and fumigation, alone or combined, on survival of Fusarium oxysporum f. sp. radicis-lycopersici, F. o. lycopersi, Phytophthora nicotianae (=P. parasitica), and Peudomonas solanacearum were examined in field plots in northern Florida. Soil solarization was performed over a 32- to 49-day period using a photoselective, low-density polyethylene film. Soil was fumigated with a 67:33 mixture of methyl bromide:chloropicrin. Precipitation occurred on 14 and 23 days during solarization periods in 1992 and 1993, respectively

Influence of site factors on dogwood anthracnose in the Nantahala Mountain range of western North Carolina

D. O., Britton, K. O., and Swank, W. T. 1992. Influence of site factors on dogwood anthracnose in the Nantahala Mountain range of western North Carolina. Plant Dis. 76:915-918. Sixty-five 0.08-ha plots located within the Nantahala Mountain range of western North Carolina were surveyed for dogwood anthracnose, caused by Discula destructive!. The incidence of disease and disease severity (extent of foliar symptoms and limb dieback) within canopies of Cornus florida was determined for all trees with a diameter of 1.0 cm or greater at 1.37 m aboveground. The incidence of dogwood anthracnose ranged from 53 to 100%; the severity of foliar symptoms, from 3 to 65%; and limb dieback, from 8 to 65%. Plots were inventoried, and the relationship between dogwood anthracnose and 14 variables representing indices of host density, stand composition, and topography was examined. Host density or relative host density, expressed in stems per hectare or importance value, respectively, and azimuth accounted for a significant portion of explainable variation in dogwood anthracnose. Anthracnose was inversely related to absolute or relative measurements of host density. Disease was greatest in northeast-facing plots and lowest in southwest-facing plots. Elevation had a minor influence on disease incidence and limb dieback. Geographic features, as described by the landform index, had a minor influence on disease incidence.

A standardized approach for estimating the permeability of plastic films to soil fumigants under various field and environmental conditions.

Minimizing atmospheric emissions of soil fumigants is critical for protecting human and environmental health. Covering the soil surface with a plastic tarp is a common approach to restrict fumigant emissions. The mass transfer of the fumigant vapors through the tarp is often the rate-limiting factor in fumigant emissions. An approach for standardizing measurements of film permeability is proposed that is based on determining the resistance (R) of films to diffusion of fumigants. Using this approach, values were determined for more than 200 film-chemical combinations under a range of temperature, relative humidity, and film handling conditions. Resistance to diffusion was specific for each fumigant/film combination, with the largest range of values observed for the fumigant chloropicrin. For each fumigant, decreased with increasing temperature. Changes in film permeability due to increases in temperature or field installation were generally less than a factor of five. For one film, values determined under conditions of very high relative humidity (approximately 100%) were at least 100 times lower than when humidity was very low (approximately 2%). This approach simplifies the selection of appropriate films for soil fumigation by providing rapid, reproducible, and precise measurements of their permeability to specific fumigants and application conditions.

Yield potential and soil quality under alternative crop production practices for fresh market pepper

This study was conducted in Florida in 1999 and 2000 to examine the impact of alternative crop production practices on soil quality and yields of fresh market pepper ( Capsicum annuum ). Replicated field plots were established on an organic vegetable farm that had been under certification for 5 years and on a conventional pepper farm that had been fumigated with methyl bromide for 25 consecutive years. Production practices evaluated included raised beds covered by white plastic mulch, soil solarization, no-till in a stubble crop of sunn hemp ( Crotolaria juncea ) or iron-clay pea ( Vigna unguiculata ) and the addition of 67 t ha −1 of urban plant debris (UPD). Soil fumigation with methyl bromide–chloropicrin was also evaluated at the conventional farm site. Soil organic carbon significantly increased following the addition of UPD in both years at the organic site but only in the second year at the conventional site. Cation exchange capacity increased significantly after addition of UPD in both years at both sites and a significant interaction with production practices was observed in the second year at the organic site. Soil phosphorus levels were high at both sites but were not impacted by production practices or UPD. In 1999, the addition of UPD significantly decreased soil nitrate levels at the organic site and the conventional site, except under the no-till treatments. In 2000, soil nitrate levels were not affected by UPD or production practice. Stand counts, determined by the number of surviving pepper plants 21–28 days after transplanting, were severely impacted in no-till treatments due to intense competition from weeds. Marketable yields equal to, or above, the 1999/2000 statewide average for conventional production systems were obtained with soil fumigation and soil solarization at the conventional site in 1999. In 2000, an epidemic of Phytophthora blight ( Phytophthora capsici ) eliminated production at the conventional site. Marketable yield at the organic site approached the statewide average for conventional systems under the solarization treatment. Yields under plastic mulch were increased at both sites with the addition of UPD. The results demonstrated that organic pepper yields from soil-solarized plots were similar to yields obtained by conventional farmers using high inputs of rapidly mobile nitrogen sources. However, no-till systems for fall production do not appear to be a viable alternative under Florida conditions due to the rapid proliferation of weeds under the cover crop stubble. The addition of urban plant debris was associated with an increase in soil organic carbon and cation exchange capacity in sandy soils typical of those found in Florida.

An alternative, low-input production system for fresh market tomatoes

An alternative, low-input production system for fresh market tomato was developed using strip tillage practices in conjunction with established bahiagrass pasture. The alternative system was designed to reduce the impact of soilborne pests, minimize agricultural inputs, improve soil conservation and optimize yields. Field experiments indicate that competition from bahiagrassfor nutrients within the tilled strips significantly impacted yield. Selective colonization of tomato roots by arbuscular mycorrhizal fungi isolated from field plots was observed. Damage from root-knot nematodes was minimized by planting tomato into established bahiagrass pastures. The alternative system was validated on a commercial tomato production farm in a side by side comparison with a conventional production system consisting of raised beds, fumigated with methyl bromide and covered by black polyethylene plastic. Yields were 6.5 t/ha greater under the conventional system. However, the net return was

Soil Fate of Agricultural Fumigants in Raised-Bed, Plasticulture Systems in the Southeastern United States

568/ha greater in the alternative system. The results indicate that the alternative system has the potential to replace or supplement the conventional production system.

Biological Impact of Divergent Land Management Practices on Tomato Crop Health

Soil concentrations and degradation rates of methyl isothio-cyanate (MITC), chloropicrin (CP), 1,3-dichloropropene (1,3-D), and dimethyl disulfide (DMDS) were determined under fumigant application scenarios representative of commercial raised bed, plastic mulched vegetable production systems. Five days after application, 1,3-D, MITC, and CP were detected at concentrations up to 3.52, 0.72, and 2.45 μg cm, respectively, in the soil atmosphere when applications were made in uniformly compacted soils with a water content >200% of field capacity and covered by a virtually impermeable or metalized film. By contrast, DMDS, MITC, and CP concentrations in the soil atmosphere were 0.81, 0.02, and 0.05 μg cm, respectively, 5 d after application in soil containing undecomposed plant residue, numerous large (>3 mm) clods, and water content below field capacity and covered by low-density polyethylene. Ranked in order of impact on the persistence of fumigants in soil were soil water content (moisture), soil tilth (the physical condition of soil as related to its fitness as a planting bed), the type of plastic film used to cover fumigated beds, and soil texture. Fumigants were readily detected 13 d after application when applied in uniformly compacted soils with water contents >200% of capacity and covered by a virtually impermeable or metalized film. By contrast, 1,3-D and MITC had dissipated 5 d after application in soils with numerous large (>3 mm) clods and water contents below field capacity that were covered by low-density polyethylene. Soil degradation of CP, DMDS, and MITC were primarily attributed to biological mechanisms, whereas degradation of 1,3-D was attributed principally to abiotic factors. This study demonstrates improved soil retention of agricultural fumigants in application scenarios representative of good agricultural practices.

Adaptation of approaches to pest control in low-input agriculture

Development of sustainable food systems is contingent upon the adoption of land management practices that can mitigate damage from soilborne pests. Five diverse land management practices were studied for their impacts on Fusarium wilt (Fusarium oxysporum f. sp. lycopersici), galling of roots by Meloidogyne spp. and marketable yield of tomato (Solanum lycopersicum) and to identify associations between the severity of pest damage and the corresponding soil microbial community structure. The incidence of Fusarium wilt was >14% when tomato was cultivated following 3 to 4 years of an undisturbed weed fallow or continuous tillage disk fallow rotation and was >4% after 3 to 4 years of bahiagrass (Paspalum notatum) rotation or organic production practices that included soil amendments and cover crops. The incidence of Fusarium wilt under conventional tomato production with soil fumigation varied from 2% in 2003 to 15% in 2004. Repeated tomato cultivation increased Fusarium wilt by 20% or more except when tomato was grown using organic practices, where disease remained less than 3%. The percent of tomato roots with galls from Meloidogyne spp. ranged from 18 to 82% in soil previously subjected to a weed fallow rotation and 7 to 15% in soil managed previously as a bahiagrass pasture. Repeated tomato cultivation increased the severity of root galling in plots previously subjected to a conventional or disk fallow rotation but not in plots managed using organic practices, where the percentage of tomato roots with galls remained below 1%. Marketable yield of tomato exceeded 35 Mg ha(-1) following all land management strategies except the strip-tillage/bahiagrass program. Marketable yield declined by 11, 14, and 19% when tomato was grown in consecutive years following a bahiagrass, weed fallow, and disk rotation. The composition of fungal internal transcribed spacer 1 (ITS1) and bacterial 16S rDNA amplicons isolated from soil fungal and bacterial communities corresponded with observed differences in the incidence of Fusarium wilt and severity of root galling from Meloidogyne spp. and provided evidence of an association between the effect of land management practices on soil microbial community structure, severity of root galling from Meloidogyne spp., and the incidence of Fusarium wilt.

Development and Deployment of Systems-Based Approaches for the Management of Soilborne Plant Pathogens

Abstract Adaptation and acceptance of pest control in low-input agriculture will be largely influenced by the approach used to manage soil-borne pests. A single tactic approach, consisting of the routine application of a broad spectrum biocide or biocides to disinfest soil is not compatible with the goal of minimizing inputs and will not have wide-scale applicability in low-input production systems. An integrated pest management (IPM) approach can be compatible with low-input systems but is often difficult to implement due to inherent constraints associated with identifying and treating organisms in the soil. Additionally, IPM will require more intensive knowledge of biological interactions in the soil and the timely management of that information, which may not be practical in low input systems. A pro-active approach, in which the production system is designed to avoid the outbreak of pests, minimizes the use of inputs in crop production by reducing the need for intervention treatments. Traditionally, the impact of soil-borne pests is not considered until after the production system has been designed and implemented. Combining biologically based pest control methods with a production system designed to minimize their impacts offers the most sustainable approach for low-input agriculture.