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.

Exposure Time to Lethal Temperatures for Meloidogyne incognita Suppression and Its Implication for Soil Solarization.

Meloidogyne incognita eggs or J2 were incubated in test tubes containing sand:peat mix and immersed in a water bath heated to 38, 39, 40, 41, 42, 43, 44 and 45 degrees C for a series of time intervals. Controls were maintained at 22 degrees C. Nematodes surviving or hatching were collected from Baermann trays after three weeks of incubation. Regression analyses between percent survival or egg hatch and hours of heat treatment were performed for each temperature. Complete suppression of egg hatch required 389.8, 164.5, 32.9, 19.7 and 13.1 hours at 38, 39, 40, 41 and 42 degrees C, respectively. Complete killing of J2 required 47.9, 46.2, 17.5 and 13.8 hours at 39, 40, 41 and 42 degrees C, respectively. J2 were not completely killed at 38 degrees C within 40 hours of treatment, but were killed within one hour at 44 and 45 degrees C. Effect of temperature on nematode killing is not determined by heat units. Oscillating temperature between cool and warm did not interfere with the nematode suppressive effect by the heat treatment. Six-week solarization in the field during the summers of 2003 and 2004 in Florida accumulated heat exposure times in the top 15 cm of soil that surpassed levels required to kill M. incognita as determined in the water bath experiments. Although near zero M. incognita were detected right after solarization, the nematode population densities increased after a cycle of a susceptible pepper crop. Therefore, future research should address failure of solarization to kill nematodes in the deeper soil layers.

Saline Irrigation Affects Belonolaimus longicaudatus and Hoplolaimus galeatus on Seashore Paspalum.

Seashore paspalum (Paspalum vaginatum) has great potential for use in salt-affected turfgrass sites. Use of this grass on golf courses, athletic fields, and lawns in subtropical coastal areas may aid in conservation of freshwater resources. Belonolaimus longicaudatus and Hoplolaimus galeatus are considered among the most damaging root pathogens of turfgrasses in Florida. Glasshouse experiments were performed in 2002 and 2003 to examine the effects of increasing levels of irrigation salinity on B. longicaudatus and H. galeatus. Irrigation treatments were formulated by concentrating deionized water to six salinity levels (0, 5, 10, 15, 20, and 25 dS/m). Final population densities of H. galeatus followed a negative linear regression (r(2) = 0.92 and 0.83; P <= 0.01) with increasing salinity levels. Final population densities of B. longicaudatus were quadratically (r(2) = 0.72 and 0.78; P <= 0.01) related to increasing salinity levels from 0 to 25 dS/m. An increase in population densities of B. longicaudatus was observed at moderate salinity levels (10 and 15 dS/m) compared to 0 dS/m. Root-length comparisons revealed that B. longicaudatus caused root stunting at low salinity levels, 0 to 10 dS/m, but roots were not affected at 15 to 25 dS/m. These results indicate that the ability of B. longicaudatus to feed and stunt root growth was negatively affected at salinity levels of 15 dS/m and above.

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.

Reduction of Phytophthora Blight of Madagascar Periwinkle in Florida by Soil Solarization in Autumn.

Three field experiments were conducted in southwest and west-central Florida in 1993 through 1995 to evaluate the effectiveness of soil solarization during autumn in reducing Phytophthora blight of Madagascar periwinkle (Catharanthus roseus) caused by Phytophthora nicotianae. Plots (3.6 by 3.6 m) were infested by incorporating winter wheat seed containing P. nicotianae in the upper 15 cm of soil. Solarization was then conducted for 21 to 41 days, primarily during October, using clear, 25- or 50-µm low-density polyethylene mulch. The progress of Phytophthora blight, monitored for 31 to 42 days following planting, was significantly reduced by solarization in all experiments, and final blight incidence was reduced in two of three experiments. Solarization also reduced population densities of P. nicotianae.

Reduction of Landscape Pathogens in Florida by Soil Solarization.

Two experiments were conducted during autumn 1997 and 1998 in west-central Florida to evaluate the effectiveness of soil solarization alone and in combination with the biological control agents Streptomyces lydicus (Actinovate) and Pseudomonas chlororaphis (syn. P. aureofasciens, AtEze) and the reduced-risk fungicide fludioxonil (Medallion) in managing soilborne pathogens of impatiens (Impatiens × wallerana, 'Accent Burgundy'). Naturally infested soil was solarized for 47 or 48 days during September and October using two layers of 25-µm clear, low-density polyethylene mulch, separated by an air space of up to 7.5 cm. Solarization decreased the final incidence and progress of Rhizoctonia crown rot and blight, incidence of Pythium spp. in roots, and root discoloration, and increased shoot biomass in both experiments. The technique also consistently reduced root-knot severity and population densities of Meloidogyne incognita, Dolichodorus heterocephalus, Paratrichodorus minor, and Criconemella spp. The incidence of Rhizoctonia crown rot and blight was reduced by fludioxonil, but not by the biological control agents.

Effect of silver reflective mulch and a summer squash trap crop on densities of immature Bemisia argentifolii (Homoptera: Aleyrodidae) on organic bean.

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.

Simulated sampling strategies for nematodes distributed according to a negative binomial model.

A FORTRAN computer program was developed to simulate nematode soil sampling strategies consisting of various numbers of samples per field, with each sample consisting of various numbers of soil cores. The program assumes that the nematode species involved fit a negative binomial distribution. Required input data are estimates of the mean and k values, the number of samples per field and cores per sample in the strategy to be investigated, and the number of times the simulation is to be replicated. Output consists of simulated values of the relative deviation from the mean and standard error to mean ratio, both averaged over all replications. The program was used to compare 150 simulated sampling strategies for Meloidogyne incognita, involving all combinations of two mean values (2.0 and 10.0 la.rvae/10 cm(3) soil), three k values (1.35, 0.544, and 0.294), five different numbers of samples per field (1, 2, 4. 10, 20), and five different numbers of cores per sample (1, 2, 4, 10, 20). Simulations resulting from different mean values were similar, but best results were obtained with higher k values and 20 cores per sample. Relatively few 20-core samples were needed to obtain average deviations from the mean of 20-25%.

Host Suitability of Potential Cover Crops for Root-knot Nematodes.

Several potential cover crops were evaluated for their susceptibility to Meloidogyne arenaria race 1, M. incognita race 1, and M. javanica in a series of five greenhouse experiments. No galls or egg masses were observed on roots of castor (Ricinus communis), cowpea (Vigna unguiculata cv. Iron Clay), crotalaria (Crotalaria spectabilis), or American jointvetch (Aeschynomene americana). Occasional egg masses (rating

Determining consistency of spatial dispersion of nematodes in small plots.

Nematode population densities in field plots were estimated by collecting samples consisting of 12 soil cores. Plots encompassed a variety of plant hosts and sampling dates, and provided data on the population densities of seven species of plant-parasitic nematodes. Three separate samples were collected per plot on each sampling date to obtain estimates of the mean and variance of numbers for each species. For each nematode species, these estimates were used to derive the Taylor's Power Law regression over plots having identical hosts and sampling dates. For some nematode species, comparisons of regression equations among different sampling dates on the same host revealed similarities in values of a and b from Taylor's Power Law. Parameters of Taylor's Power Law relationships were used to develop sampling plans and to obtain estimates of sample precision. Precision estimates from specific and general sampling plans are illustrated for Belonolaimus longicaudatus.

Extraction Efficiency of Belonolaimus longicaudatus from Sandy Soil.

Numbers of Belonolaimus longicaudatus extracted from sandy soils (91-92% sand) by sieving and centrifugation were only 40-55% of those extracted by sieving and incubation on a Baermann tray. Residues normally discarded at each step of the sieving plus Baermann tray extraction procedure were examined for nematodes to obtain estimates of extraction efficiencies. For third-stage and fourth-stage juveniles, males, and females, estimates of extraction efficiency ranged from 60 to 65% in one experiment and 73 to 82% in another. Estimated extraction efficiencies for second-stage juveniles were lower (33% in one experiment, 67% in another) due to losses during sieving. When sterilized soil was seeded with known numbers of B. longicaudatus, 60% of second-stage juveniles and 68-76% of other stages were recovered. Most stages of B. longicaudatus could be extracted from these soils by sieving plus Baermann incubation with an efficiency of 60-70%.

Nematode population changes and forage yields of six corn and sorghum cultivars.

Two temperate corn (Zea mays) hybrids (Pioneer 3320 and Northrup King 508), two tropical corn cultivars (Pioneer X304C hybrid and Florida SYN-1 experimental open pollinated cultivar), the sorghum (Sorghum bicolor) x sudangrass (Sorghum sudanense) hybrid DeKalb SX-17, and the sorghum hybrid DeKalb FS25E were compared for effect on nematode densities and forage yield in three plantings (one single-crop and one double-crop system) in Florida. Final population densities of Meloidogyne incognita in the three plantings ranged from 0 to 13/100 cm(3) soil on the two Sorghum spp. and were lower (P

Evaluation of Two Soybean Cultivars and Aldicarb Treatment in Soil Infested with Plant-parasitic Nematodes.

The soybean cultivars Davis and Leflore were grown in a northern Florida experimental site infested with eight species of plant-parasitic nematodes. Meloidogyne incognita appeared to become the predominant pathogen, suppressing Davis soybean yield regardless of aldicarb treatment. Soybean yields of Leflore were 1.4-fold to 3.5-fold greater than yields of Davis, but aldicarb did not affect yields of either cultivar. Davis soybean yield was negatively correlated with the at-plant density of M. incognita, whereas Leflore seed yield was not negatively correlated with any nematode.

Energetics of Meloidogyne incognita on Resistant and Susceptible Alyceclover Genotypes.

To determine the energy cost of a population of Meloidogyne incognita on the roots of alyceclover, nematode biomass was estimated and equations in the literature were used to calculate energy budgets. Amounts of energy consumed, respired, or used in production of nematode biomass were calculated. Results suggested that severe infestations of root-knot nematodes can remove significant quantities of energy from their hosts. Over a 36-day period, a population of 2.6 females of M. incognita per root system removed less than 0.4 calories of energy from a resistant alyceclover plant but over 11 calories were removed by 28 females from a susceptible alyceclover. The calculations indicate that on the resistant alyceclover line, 53% of the energy assimilated by the root-knot population was allocated to respiration, with only 47% allocated to production, whereas on the susceptible line, 65% of the assimilated energy was allocated to production. Such energy demands by the parasite could result in significant reductions in yield quantity and quality at a field production level.

Population Dynamics of Plant-parasitic Nematodes on Cover Crops of Corn and Sorghum.

Buildup of plant-parasitic nematode populations on corn (Zea mays), soybean (Glycine max), and sorghum (Sorghum bicolor) were compared in 1991 and 1992. Final population densities (Pf) of Meloidogyne incognita were lower following sorghum than after soybean in both seasons, and Pf after sorghum was lower than Pf after corn in 1992. In both seasons, Pf differed among the sorghum cultivars used. No differences in Pf on corn, sorghum, and soybean were observed for Criconemella spp. (a mixture of C. sphaerocephala and C. ornata) or Paratrichodorus minor in either season. Pf levels of Pratylenchus spp. (a mixture of P. brachyurus and P. scribneri) were greatest after corn in 1992, but no differences with crop treatments were observed in 1991. When data from field tests conducted with corn and sorghum during the past four seasons were pooled, negative linear relationships between ln(Pf/Pi) and ln(Pi) were observed for Criconemella spp. and P. minor on each crop, and for M. incognita on corn (Pi = initial population density). Although ln(Pf/Pi) and ln(Pi) were not related for M. incognita with pooled sorghum data, separate relationships were derived for various sorghum cultivars. Regression equations from pooled data were used to obtain estimates of equilibrium density and maximum reproductive rate, and these estimates were used to construct models expressing nematode Pf across a range of initial densities. Many of these models were robust, encompassing a range of sites, season, crop cultivars, and planting dates. Quadratic models derived from pooled field data provided an alternative method for expressing Pf as a function of Pi.

Effect of crop rotation and tillage on nematode densities in tropical corn.

Effects of tillage and crop rotation on nematode densities in tropical corn (Zea mays cv. Pioneer X304C) were examined in a factorial experiment with two rotation crops and two tillage practices (no-till vs. conventional-till), conducted in each of three seasons (1990-1992) in north Florida. The rotation treatments consisted of sorghum (Sorghum bicolor cv. DeKalb BR64) or soybean (Glycine max) grown during the 1989 season. Densities of Meloidogyne incognita (race 1) remained lower throughout the growing season in corn following sorghum than in corn plots following soybean. This effect was observed clearly even in the third consecutive corn crop. In 1990, densities of Criconemella spp. were initially higher in plots planted to sorghum the previous year, but by the end of the subsequent corn crop, no differences were evident. Paratrichodorus minor and Pratylenchus spp. (primarily P. scribneri) were mostly unaffected by the crop rotation treatments, but in a few instances, Pratylenchus spp. densities were higher in conventional than in no-till plots. In general, tillage had little effect on densities of most nematodes examined, and rotation appears to be more important than tillage for managing plant-parasitic nematodes under these conditions.

Effects and dynamics of a nematode community on maize.

Relationships between nematode density and yield and between final and preplant population levels were examined in small maize plots on sandy soils in north-central Florida. Plant-parasitic nematodes present in the community included Belonolaimus longicaudatus, Criconemella sphaerocephala, Meloidogyne incognita, Paratrichodorus minor, Pratylenchus brachyurus, and a Xiphinema sp. Plant growth--including stand count, grain yield, stalk weight, and size of young plants--often was inversely correlated (P

Effects and dynamics of a nematode community on soybean.

The relationships between densities of all members of a plant-parasitic nematode community and yield of 'Davis' soybean and between final and preplant population levels were examined in small plots on sandy soils in north-central Florida. Plant-parasitic nematodes present in the community included Belonolaimus longicaudatus, Criconemella sphaerocephala, Meloidogyne incognita, Paratrichodorus minor, Pratylenchus brachyurus, and Xiphinema sp. Plant growth, including stand count, soybean yield (kg/ha), and size of young plants, was occasionally inversely correlated (P

Effects of Root-knot Nematodes on Areca catechu.

No root galling or egg mass formation was noted on betel palm (Areca catechu) 3 or 9 months after inoculation with Meloidogyne arenaria, M. hapla, M. incognita races 1 and 3, or M. javanica. Compared with uninoculated controls, a reduction (P

Vertical Distribution of Plant-parasitic Nematodes in Sandy Soil under Soybean.

Vertical distribution of five plant-parasitic nematodes was examined in two north Florida soybean fields in 1987 and 1988. Soil samples were collected from 0-15 cm, 15-30 cm, and 30-45 cm deep at each site. Soil at the three depths consisted of approximately 96% sand. More than 50% of Belonolaimus longicaudatus population densities occurred in the upper 15-cm soil layer at planting, but the species became more evenly distributed through the other depths as the season progressed. Criconemella sphaerocephala was evenly distributed among the three depths in one field but was low (< 20% of the total density) in the upper 15 cm at a second site. Maximum population densities of Pratylenchus brachyurus were observed at 15-30 cm on most sampling dates. Vertical distributions of Meloidogyne incognita and Paratrichodorus minor were erratic and showed seasonal variation. A diagnostic sample from the upper 0-15 cm of these soybean fields revealed only a minority of the populations of most of the phytoparasitic species present.