R. McSorley

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.

Nematode communities as indicators of status and processes of a soil ecosystem influenced by agricultural management practices

Abstract Nematode communities were monitored for three years in a citrus soil ecosystem in Central Florida under various agricultural regimes comparing standard vs. reduced-input practices. Differences in agricultural regimes consisted of two fertilization levels, two irrigation levels, and two types of ground cover under the tree (herbicide vs. mulch). While some nematodes were affected sporadically by fertilization and irrigation treatments, mulch had a consistent and frequently significant effect on many bacterivores, fungivores, herbivores, and omnivores. Rhabitidae, Cephalobus, Aphelenchus, and Aphelenchoides had an immediate but temporary response to mulch additions. Acrobeles, Acrobeloides, Eucephalobus, Teratocephalus, Criconemoides, Aporcelaimellus, and Eudorylaimus were always less abundant in mulch-treated plots, whereas Plectus and Belonolaimus were always more abundant. Of various indices of community composition, only maturity indices, unlike diversity indices, indicated the status and intensity of soil processes (decomposition, mineralization). However, different responses of single genera within a trophic group implied unique contributions of nematode genera in soil ecosystem processes on a temporal scale, suggesting that generic or possibly species level of resolution provide the most adequate information about the soil ecosystem.

ADAPTATIONS OF NEMATODES TO ENVIRONMENTAL EXTREMES

Abstract Nematodes are a highly diverse group of organisms that show a variety of adaptations to extremes in soil and plant environments. Developmental dormancy and diapause are important for seasonal survival and long-term longevity of eggs in some species, whereas changing sex ratios may improve survival chances of the next generation in some instances. More direct and immediate responses to environmental conditions include aggregation or the formation of relatively resistant dauer larvae. Many nematodes can undergo temporary quiescence in response to environmental stress, and entry into anhydrobiosis or other extreme states allows long-term survival in unusually stressful environments. These inactive survival stages may make up a substantial proportion of the nematode population in some terrestrial environments.

Comparison of soil extraction methods for nematodes and microarthropods

Abstract Active extraction techniques, dependent on the behavior of soil animals, and passive techniques, dependent on specific gravity or sedimentation rate, are widely used in the extraction of both nematodes and microarthropods. No method is completely suitable for extraction of both nematodes and microarthropods. Since no extraction method is 100% efficient, the estimation of extraction efficiency can provide a basis for evaluating extraction performance and comparing results of different methods.

Comparison of Different Sampling Methods and Effect of Pesticide Application on Spider Populations in Lime Orchards in South Florida

Abstract A survey of predatory arthropods in lime orchards at Homestead, FL, showed that spiders significantly outnumbered the other predatory arthropods (the green lacewing Chrysoperla rufilabris, coccinellid Harmonia sp., and the ant Myrmelachista sp.). The spider community consisted of nine families, 25 genera, and 15 species. The abundance and diversity of the predatory spiders in lime orchards suggests their possible role in regulating the increase of arthropod pest populations. In general, comparison of three sampling methods revealed that the visual sampling method provided the highest number of spiders collected followed by the shake-cloth method and the DVAC suction method collected the least. However, our data showed that the choice of sampling method depends on the species of interest. For instance, spider species in the hunting group were collected frequently using the visual method followed by the shake-cloth method; whereas, most of the species in the web-building group were collected by the three sampling methods with similar frequencies. The difference in the efficiency of the sampling methods may be explained by the retreating habits of the different spider species. The data gathered in sampling the predatory arthropods in sprayed and nonsprayed lime orchards demonstrated the probable nontarget effect of the different pesticides used in the orchards.

Relationship of crop and rainfall to soil nematode community structure in perennial agroecosystems

Abstract Population densities in soil of nematodes belonging to different genera were monitored for 3 years in a citrus grove and an adjacent bahiagrass pasture in Florida, USA, to determine whether indices of community structure or densities of key genera were more useful in characterizing the soil nematode communities of these very different perennial agroecoystems. Population densities of Acrobeles, Aphelenchus, Cervidellus, Ironus, Paratrichodorus, and Zeldia were consistently greater (P⪯0.10) 0.10) in the citrus site, where 64% to 83% of the nematodes found were bacterivores and only 1 % to 16% herbivores. The pasture, containing 19% to 47% bacterivores and 25% to 67% herbivores, had greater numbers of Bunonema, Criconema, Criconemella, Eucephalobus, Hemicriconemoides, Miconchus, Tylenchorhynchus, and Wilsonema. Several indices of nematode community structure also showed consistent differences with site. The Shannon-Weaver diversity index, calculated across trophic groups, was greater in the pasture, but Simpsons index and the ratio of decomposers to herbivores were greater in citrus, reflecting the preponderance of bacterivores at that site. Within each site, population densities of nematodes in several key genera were correlated with rainfall over time, but correlations between rainfall and indices of community structure were infrequent.

Effect of Organic Mulches on Soil Surface Insects and Other Arthropods

ABSTRACT Four different types of organic mulches were evaluated for their effects on soil surface insects and related arthropods. Field experiments were conducted in fall 2007 and 2008 near Citra, Florida. In both the years, five treatments were compared: cowpea (Vigna unguiculata (L.) Walp.) mulch, sunn hemp (Crotalaria juncea L.) mulch, sorghum-sudangrass (Sorghum bicolor Moench × S. sudanense ((Piper)] Stapf) mulch, pine bark nuggets, and unmulched control. Data were collected on insects and other arthropods using pitfall traps. Results indicate that organic mulches can affect a wide range of different insects. Diptera, dominated by Asyndetus spp. (Dolichopodidae), were most dense in pine bark plots in both years. Populations of small plant-feeding insects such as Aphididae, Thripidae, and Aleyrodidae were most dense in cowpea and unmulched control plots in one season. It is possible that these insects were affected by weed growth in cowpea and control plots. Ants, which tend or feed on small plant feeders, were fairly abundant in these plots as well, as were predatory beetles. Some groups, such as Collembola (mainly Isotomidae), spiders, and Orthoptera (Acrididae and Gryllidae) were unaffected by mulches.

Effect of Silver Reflective Mulch and a Summer Squash Trap Crop on Densities of Immature Bemisia argentifolii (Homoptera: Aleyrodidae) on Organic Bean

Abstract Polyethylene mulch with a reflective silver stripe and a yellow summer squash, Cucurbita pepo L., trap crop were tested alone and in combination as tactics to reduce densities of Bemisia argentifolii Bellows & Perring eggs and nymphs, and incidence of bean golden mosaic geminivirus on snap bean, Phaseolus vulgaris L. Egg densities were consistently higher on squash than on bean, but egg densities and virus incidence were not lower on bean grown with squash than on bean grown in monoculture. Silver reflective mulch reduced egg densities compared with bean grown on bare ground during the first week after crop emergence for 2 of the 3 yr that the study was conducted. However, egg suppression by silver mulch was not enhanced by the presence of a squash trap crop when both tactics were combined. The obstacles to suppressing B. argentifolii through the use of trap crops are discussed.

Comparison of Water Displacement and WinRHIZO Software for Plant Root Parameter Assessment

Water-displacement and WinRHIZO root-scanning methods were compared for efficacy of root damage assessment. Results from both methods were similar and a highly significant relationship was found between the two methods in trial one (r2 = 0.9968, P < 0.0001) and trial two (r2 = 0.9988, P < 0.0001). Both protocols provide consistent root volume measurements; however, water displacement is preferred as an economical method if a quick evaluation of a large amount of roots is essential. For a more detailed root morphological and architectural analysis, WinRHIZO root scanning provides additional information about several root parameters that cannot be measured by simple water displacement.

Potential of Field Corn as A Barrier Crop and Eggplant as A Trap Crop for Management of Bemisia Argentifolii (Homoptera: Aleyrodidae) on Common Bean in North Florida

Trap crops and barrier crops are among the cultural control methods promoted for management of Bemisia argentifolii Bellows & Perring, particularly for small farmers in the tropics. In 1996 eggplant, Solanum melongena L., was tested as a trap crop, and in 1996 and 1997 corn, Zea mays L., was tested as a barrier crop for management of B. argentifolii on bean, Phaseolus vulgaris L. In 1996 treatments were compared by sampling immature B. argentifolii on bean leaves. Neither egg nor nymphal densities were reduced by eggplant or corn treatments in 1996. In the 1997 corn barrier trial plot size was increased and the orientation of barrier row to wind direction was evaluated. A dust-and-release procedure was used to measure entry of greenhouse-reared adult B. argentifolii into experimental plots. Counts from yellow sticky traps in 1997 indicated that migration by adult whiteflies into plots was determined primarily by air currents and was only marginally influenced by the presence of a corn barrier. The results indicate that barrier crops and certain trap crops may have limited value for whitefly management.