Survey of crop losses in response to phytoparasitic nematodes in the United States for 1994.

Previous reports of crop losses to plant-parasitic nematodes have relied on published results of survey data based on certain commodities, including tobacco, peanuts, cotton, and soybean. Reports on crop-loss assessment by land-grant universities and many commodity groups generally are no longer available, with the exception of the University of Georgia, the Beltwide Cotton Conference, and selected groups concerned with soybean. The Society of Nematologists Extension Committee contacted extension personnel in 49 U.S. states for information on estimated crop losses caused by plant-parasitic nematodes in major crops for the year 1994. Included in this paper are survey results from 35 states on various crops including corn, cotton, soybean, peanut, wheat, rice, sugarcane, sorghum, tobacco, numerous vegetable crops, fruit and nut crops, and golf greens. The data are reported systematically by state and include the estimated loss, hectarage of production, source of information, nematode species or taxon when available, and crop value. The major genera of phytoparasitic nematodes reported to cause crop losses were Heterodera, Hoplolaimus, Meloidogyne, Pratylenchus, Rotylenchulus, and Xiphinema.

Evaluation of Application Methods of Metam Sodium for Management of Fusarium Crown and Root Rot in Tomato in Southwest Florida.

Experiments were conducted during 1992 to 1995 to evaluate the effectiveness of application methods of metam sodium (MS; sodium N-methyldithio-carbamate) for the management of Fusarium crown and root rot (FCRR) caused by Fusarium oxysporum f. sp. radicis-lycopersici in mulched and staked tomatoes (Lycopersicon esculentum Mill.) grown on raised beds in commercial fields in southwest Florida. Efficacy of MS was compared with soil-injection of methyl bromide-chloropicrin (MBC), the current industry practice for production of tomatoes in Flor-ida. The incidence of FCRR was consistently high in nontreated plots (80 to 100%), but disease severity varied by site, and yields were reduced by 10 to 57% at sites with high disease severity when compared to sites treated with MBC at 336 to 448 kg/ha. Application of MBC reduced FCRR incidence in all experiments. Chemigation with MS at 701 or 935 liters/ha into mulched beds using either one or two drip irrigation tubes placed on the soil surface, and soil injection of MS at 935 liters/ha, failed to reduce the disease. The application of MS at 935 liters/ha to the soil surface prior to bed formation produced variable results. Rotovation of MS at the same rate into preformed beds consistently produced reductions in the incidence of FCRR equivalent to those achieved by MBC.

Spatial Patterns of Belonolaimus spp. Among and Within Citrus Orchards on Florida's Central Ridge.

A survey was initiated to determine the incidence of Belonolaimus spp. (sting nematodes) in citrus orchards in the central ridge region of Florida, following widespread damage by these nematodes to young trees replanted after freezing weather in 1989-90. Sting nematodes were detected in 50% of 210 samples and in 64% of 84 orchards surveyed. More orchards in Polk County were infested with sting nematodes (82%) than in counties to the north (36%) or south (48%). Principal component analysis of morphometric data separated six of seven sting nematode populations in northeastern Polk County from six populations in adjacent regions. Stylet:tail ratio for nematodes in northeastern Polk County tend to be > 1.0 and were << 1.0 for all other populations. Patchiness of nematodes within an orchard was associated with stunted trees (23% smaller), reduced root mass density (25% lower), and low fruit yield (57% reduction). Soil texture did not vary among trees of different size in the orchard, but soil water potential between irrigation events was highest beneath small trees with low root mass density. Results of the survey indicate that the incidence of sting nematodes in orchards on the central ridge is much higher than previously estimated and that sting nematodes can cause substantial damage in replanted orchards. Further research is needed to evaluate the significance of sting nematode population variability and its relationship to citrus crop loss in Florida.

Standardization of reporting procedures for nematicide efficacy testing: a research and extension perspective.

Nematicide tests reported in the Annals of Applied Nematology from 1991 to 1995 were reviewed and evaluated for 24 criteria. Most criteria such as soil type, nematode density, cultivar planted, test location, and nematicide applied were reported in more than adequate detail. Soil moisture content and temperature conditions during the test, field history of pesticide use, agronomic-horticultural production practices, and measurements of yield were reported less adequately. Many reports dealing with fumigant nematicides and application by irrigation had inadequate descriptions of rates and application methodology, Although areas for improvement exist, overall the published works in Annals of Applied Nematology are well-reported experiments. Pressure exists from several elements of hematology to "standarize" reporting procedures and test practices. Due to the diversity of crops, nematodes, nematicides, edaphic and environmental conditions that affect nematicide fate, nematode activity, plant growth, and subsequently nematicide efficacy, creation of a completely standardized format is improbable. More accurate reporting of some test criteria rather than standardization will allow better comparison between tests when results do not concur and allow future researchers to duplicate application rates and methodologies to determine the sources of discrepancies between tests, including environmental variations.

The challenge of research and extension to define and implement alternatives to methyl bromide.

Over the past 30 years, methyl bromide (MBr), a broad spectrum fumigant, has been used extensively for soilborne disease and pest control in the production of many fruit, vegetable, turf, and nursery crops. Recently, agricultural emissions of MBr were implicated as a potentially significant contributor to stratospheric ozone depletion. As a precautionary measure for global ozone protection, the U.S. Environmental Protection Agency has enforced federal legislation which mandates a complete phase-out of MBr use within the United States by 1 January 2001. Thus, new cost effective, environmentally compatible strategies for control of nematodes and other soilborne pests and pathogens must be developed and tested in a relatively short time to avoid significant losses in crop productivity. The extent to which certain agricultural industries that are now heavily reliant on MBr are affected will depend on the development of sustainable, integrated tactics to pest control, such as combinations of cultural, chemical, and biological tactics. New muhidisciplinary research and extension programs must be developed to address and overcome major constraints and incompatibilities that have prevented such tactics from being widely adopted.

Application of Taylor's Power Law to Sample Statistics of Tylenchulus semipenetrans in Florida Citrus.

Taylor's Power Law was fit to Tylenchulus semipenetrans population data obtained from individual trees in a survey of 50 Florida citrus orchards (geographic survey) and to data from individual trees within a single orchard collected at regular intervals for 2 years (temporal survey). No significant differences were detected between slope or intercept values when log variance was regressed against log mean for the geographic and temporal data sets. The geographic survey was divided into two subsets of data according to the perceived size of patches of T. semipenetrans. Subsets consisted of orchards which appeared to have numerous small patches of trees infected by the nematode (small patch) and orchards in which most of the trees were infected (large patch). The slope value for the orchards with smaller patches of nematodes was different (P

Nematode-degree days, a density-time model for relating epidemiology and crop losses in perennials.

The impact of Meloidogyne hapla on alfalfa (Medicago sativa) yield was described by a multiple point damage model as a function of current plant status, cumulative pest stress, and crop history. Nematode-degree days (NDD(female symbol)), calculated on a physiologic time scale as total area under the adult female population density curve, were used to express M. hapla parasitism as cumulative nematode dosage. NDD(female symbol) increased exponentially over physiological time at rates relative to M. hapla initial population density of eggs and second-stage juveniles (Pi). Dosage accumulation rates, varying from 213 to 272 NDD(female symbol) per degree day, did not differ (P = 0.05) among six Pi levels. Cumulative yield reductions, increasing linearly with NDD(female symbol) over time to 50% of the M. hapla-free controls, were well correlated for the six initial Pi levels (r(2) = 0.93). Progressive reductions in alfalfa yields to 65% of the nematode-free controls, reflective of the prolonged exposure of the crop to M. hapla, were adequately described by NDD model estimates of either combined population densities of eggs and juveniles or adult females. Cumulative area under the combined eggs (e) and juvenile (J) population curve (NDD(e+J)) and NDD(female symbol) were linearly related (r(2) = 0.97).

Influence of Alfalfa Plant Growth on the Multiplication Rates and Ceiling Population Density of Meloidogyne hapla.

The rates of reproduction and multiplication of Meloidogyne hapla decreased as a result of self-regulatory, density-dependent processes with time and nematode population increase in the soil and roots of Medicago sativa cv. Cuf 101. Juvenile, egg, and mature female population densities increased at a maximum rate until damage to the host resulted in alfalfa yield reductions. Temporal differences in multiplication and reproduction rates of M. hapla were observed to be a function of initial population density (Pi), host damage, and root biomass, indicating increased levels of competition for a constant but limited number of feeding sites. Over time, a log linear relationship emerged between multiplication rate of M. hapla and Pi. Slopes of -0.90953 for combined eggs and juveniles and -0.71349 for mature females indicated a gradual approach to ceiling densities. Reproductive rates decreased exponentially from an initial maximal value of 200 to a relatively constant rate of 53 eggs per female.

Influence of Meloidogyne hapla on Alfalfa Yield and Host Population Dynamics.

Self-thinning in alfalfa, a dynamic process involving the progressive elimination of the weakest plants, was enhanced by Meloidogyne hapla. Alfalfa stand densities decreased exponentially with time and were reduced 62% (P = 0.05) in the presence of M. hapla. As stand densities decreased over time, mean plant weights increased at a rate 2.59 times faster in the absence of M. hapla. In a stepwise multiple regression analysis, 65% of the total variation in yield could be explained by changes in stand density and 85% by average weight of individual stems. Alfalfa yields were suppressed (P = 0.05) by M. hapla, with suppression generally increasing with time and as the nematode population density increased. Yield suppression was attributable primarily to the decline in plant numbers and to suppression in individual plant weights.

Joint Influence of Pratylenchus penetrans (Nematoda) and Leptinotarsa decemlineata (Insecta) on Solanum tuberosum Productivity and Pest Population Dynamics.

The joint action of a plant parasitic nematode, Pratylenchus penetrans (root-lesion nematode), and an insect defoliator, Leptinotarsa decemlineata (Colorado potato beetle), on growth, development, and yield of Solanum tuberosum cv. Superior was studied in the field. Three population densities of P. penetrans were superimposed on each of three population levels of L. decemlineata. The major impact of P. penetrans on final yield was through a reduction in the number of tubers formed during tuber initiation. Defoliation by L. decemlineata increased with time as larvae advanced through successive instars and densities increased. This resulted in a significant reduction in tuber weight and numbers. Total yield of S. tuberosum was decreased by 66% with increasing population densities of L. decemlineata and 27 % with increasing densities of P. penetrans. L. decemlineata feeding did not affect soil population densities of P. penetrans. Root population densities of P. penetrans, however, were significantly (P = 0.05) higher in plants maintained beetle free than in plants grown in the presence of the beetles.