Meloidogyne Haplanaria: An Emerging Threat to Tomato Production in Florida.

The Mi-gene is widely used in different tomato cultivars to resist several Meloidogyne spp. (root-kot nematode; RKN), including M. incognita, M. javanica, and M. arenaria. Tomato cultivars with the Mi-gene are widely used in fields. However, factors such as temperatures, high initial population densities, and gene dosage can interfere with the expression of this gene. In addition, the presence of virulent species of RKN can limit the usefulness of the gene. One of the virulent species is M. haplanaria, which was identified infecting RKN-resistant tomato in Florida in 2015. The objectives of this study were to determine the initial damage threshold of M. haplanaria on tomato under greenhouse conditions and to analyze the impact of temperature and genetic background on virulence in tomato cultivars. The results showed a preliminary damage threshold of three eggs and J2/cm3 of soil. In addition, it was observed that M. haplanaria has a shorter life cycle than the virulent M. enterolobii and can infect, reproduce, and damage homozygous or heterozygous RKN-resistant tomato plants. This research demonstrated that M. haplanaria should be considered highly virulent on RKN-resistant tomato and is an important threat to agriculture in Florida.

Satellite-based soil moisture provides missing link between summertime precipitation and surface temperature biases in CMIP5 simulations over conterminous United States.

Past studies have shown that climate simulations have substantial warm and dry biases during the summer in the conterminous United States (CONUS), particularly in the central Great Plains (CGP). These biases have critical implications for the interpretation of climate change projections, but the complex overlap of multiple land-atmosphere feedback processes make them difficult to explain (and therefore correct). Even though surface soil moisture (SM) is often cited as a key control variable in these processes, there are still knowledge gaps about its specific role. Here, we use recently developed remotely sensed SM products to analyse the link between spatial patterns of summertime SM, precipitation and air temperature biases over CONUS in 20 different CMIP5 simulations. We identify three main types of bias combinations: (i) a dry/warm bias over the CGP region, with a significant inter-model correlation between SM and air temperature biases (R = -0.65), (ii) a wet/cold bias in NW CONUS, and (iii) a dry/cold bias in SW CONUS. Combined with irrigation patterns, these results suggest that land-atmosphere feedbacks over the CGP are not only local but have a regional dimension, and demonstrate the added-value of large-scale SM observations for resolving the full feed-back loop between precipitation and temperature.

Exploiting soil moisture, precipitation and streamflow observations to evaluate soil moisture/runoff coupling in land surface models.

Accurate partitioning of precipitation into infiltration and runoff is a fundamental objective of land surface models tasked with characterizing the surface water and energy balance. Temporal variability in this partitioning is due, in part, to changes in pre-storm soil moisture, which determine soil infiltration capacity and unsaturated storage. Utilizing the NASA Soil Moisture Active Passive Level-4 soil moisture product in combination with streamflow and precipitation observations, we demonstrate that land surface models (LSMs) generally underestimate the strength of the positive rank correlation between pre-storm soil moisture and event runoff coefficients (i.e., the fraction of rainfall accumulation depth converted into stormflow runoff during a storm event). Underestimation is largest for LSMs employing an infiltration-excess approach for stormflow runoff generation. More accurate coupling strength is found in LSMs that explicitly represent sub-surface stormflow or saturation-excess runoff generation processes.

L-band microwave remote sensing and land data assimilation improve the representation of pre-storm soil moisture conditions for hydrologic forecasting.

Recent advances in remote sensing and land data assimilation purport to improve the quality of antecedent soil moisture information available for operational hydrologic forecasting. We objectively validate this claim by calculating the strength of the relationship between storm-scale runoff ratio (i.e., total stream flow divided by total rainfall accumulation in depth units) and pre-storm surface soil moisture estimates from a range of surface soil moisture data products. Results demonstrate that both satellite-based, L-band microwave radiometry and the application of land data assimilation techniques have significantly improved the utility of surface soil moisture data sets for forecasting stream flow response to future rainfall events.

Field efficacy of furfural as a nematicide on turf.

A commercial formulation of furfural was recently launched in the United States as a turfgrass nematicide. Three field trials evaluated efficacy of this commercial formulation on dwarf bermudagrass putting greens infested primarily with Belonolaimus longicaudatus, Meloidogyne graminis, or both these nematodes, and in some cases with Mesocriconema ornatum or Helicotylenchus pseudorobustus. In all these trials, furfural improved turf health but did not reduce population densities of B. longicaudatus, M. graminis, or the other plant-parasitic nematodes present. In two additional field trials, efficacy of furfural at increasing depths in the soil profile (0 to 5 cm, 5 to 10 cm, and 10 to 15 cm) against B. longicaudatus on bermudagrass was evaluated. Reduction in population density of B. longicaudatus was observed in furfural-treated plots for depths below 5 cm on several dates during both trials. However, no differences in population densities of B. longicaudatus were observed between the furfural-treated plots and the untreated control for soil depth of 0 to 5 cm during either trial. These results indicate that furfural applications can improve health of nematode-infested turf and can reduce population density of plant-parasitic nematodes in turf systems. Although the degree to which turf improvement is directly caused by nematicidal effects is still unclear, furfural does appear to be a useful nematode management tool for turf.

Factors affecting furfural as a nematicide on turf.

Recently a furfural nematicide Multiguard Protect EC was launched for use on turfgrasses in the United States. A series of greenhouse experiments were conducted to determine the concentration and exposure time required for this formulation to irreversibly affect Belonolaimus longicaudatus, and to study factors that might affect the practicality of furfural use in turfgrass systems. One experiment exposed B. longicaudatus to increasing concentrations of furfural (0 to 990 ppm) in vitro for either 24 or 48 hr, followed by inoculation onto bermudagrass. A second experiment evaluated effects of exposure of B. longicaudatus to increasing concentrations of furfural in soil solution on bermudagrass with or without an organic thatch layer. A third experiment evaluated effects on B. longicaudatus of increasing concentrations of furfural applied as a spray treatment to creeping bentgrass. Results from the in vitro exposure experiment found decreasing numbers of B. longicaudatus with increasing furfural concentration beginning with the lowest concentration tested (270 ppm). Belonolaimus longicaudatus were virtually eliminated with furfural concentrations ≥ 720 ppm. Similarly, exposure to increasing concentration of furfural in soil solution resulted in increasing reduction in numbers of B. longicaudatus. Presence of thatch slightly reduced the population density of B. longicaudatus. Spray application of furfural only reduced numbers of B. longicaudatus at the two highest rates (3,600 and 4,950 ppm).

First Report of Meloidogyne marylandi Infecting Bermudagrass in Florida.

Root-knot nematodes (Meloidogyne spp.) are common parasites attacking turfgrasses in the United States, but the species of these nematodes is typically unresolved unless targeted surveys are performed (3). Using morphometric analysis and an RFLP method (3), an investigation of a golf course green in Florida with a history of infestation by root-knot nematodes was conducted to identify the species present. This 'Tifdwarf' bermudagrass (Cynodon dactylon × C. transvaalensis) putting green at the University of Florida Research Unit in Citra, FL, exhibited irregular patches of declining turf. Turf roots in these symptomatic areas had galled root tips with adhering egg masses, characteristic of infection from Meloidogyne spp. Mean populations of 5,149 ± 708 Meloidogyne second stage juveniles per 100 cm3 of soil were extracted from the rhizosphere of these symptomatic plants. Morphological measurements from 20 of these juveniles were slightly less than those published previously for M. marylandi, but were still distinct enough to discriminate them from M. graminis, which commonly infects bermudagrass in Florida (3). Body length averaged 396.1 ± 4.9 (376.7 to 420.0) µm with a mean width of 16.3 ± 0.5 (13.3 to 18.3) µm, stylet lengths were 11.2 ± 0.7 (6.7 to 12.3) µm, tail lengths averaged 54.7 ± 1.9 (47.5 to 65.0) µm with the hyaline region of the tails 9.9 ± 0.7 (8.3 to 14.2) µm. Mature females extracted from symptomatic root tissue lacked a posterior cone-like protuberance of the vulva typical of M. graminis. DNA was extracted from 15 single juveniles using a NaOH digestion method (2). The mitochondrial DNA region was amplified with PCR using the primers C2F3/1108 5'-GGTCAATGTTCAGAAATTTGTGG-3' and 5'-TACCTTTGACCAATCACGCT-3' (3). This resulted in a DNA fragment 520 bp in length, which upon digestion with SspI restriction enzyme produced four bands 148, 103, 91, and 67 bp in length, similar to what has been reported for M. marylandi (3). The PCR products were purified with a QIAquick PCR purification kit (QIAGEN, Valencia, CA) and sequenced at the University of Florida, Cancer Research and Genetics Institute. Sequences were compared with those in GenBank by means of BLAST search. The comparison showed a sequence similarity of 98% with M. marylandi (GenBank Accession No. JN241918.1). Although M. marylandi has been reported on bermudagrass in many areas of the United States and other places throughout the world (1,3,4), to our knowledge, this is the first detection of this nematode in Florida. Further studies will be conducted to determine the prevalence, incidence, severity of damage caused by M. marylandi, and determine a possible mode of dispersal on turfgrasses. References: (1) A. M. Golden. J. Nematol. 21:453, 1989. (2) J. Hübschen et al. Euro. J. Plant Pathol. 110:779, 2004. (3) M. A. McClure et al. Plant Dis. 96:635, 2012. (4) Y. Oka et al. Nematol. 5:727, 2003.

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.

Effects of Belonolaimus longicaudatus Management and Nitrogen Fertility on Turf Quality of Golf Course Fairways.

Field experiments evaluated the effects of nematicide and fertility on performance of 'Tifway 419' bermudagrass parasitized by the sting nematode (Belonolaimus longicaudatus). Plot treatments were nontreated or nematicide (1,3-dichloropropene) treated combined with different nitrogen (N) fertilizer levels. Effects of treatments on numbers of B. longicaudatus and turf performance were compared. Nematicide consistently reduced numbers of B. longicaudatus, but fertilizer level had no effect on B. longicaudatus. Turf performance of nematicide-treated plots was improved compared with nontreated plots during both experiments. Increasing N fertilizer level improved turf performance in nematicide-treated plots in some cases, but had no effect on turf performance in nontreated plots in either experiment. Results suggest that increasing N fertilizer levels may not improve turf performance at sites infested with B. longicaudatus unless nematode management tactics are effective in reducing nematode densities.

Influence of Belonolaimus longicaudatus on Nitrate Leaching in Turf.

Experiments were conducted to quantify the effects of the sting nematode (Belonolaimus longicaudatus) on root reductions and quantity of nitrate (NO(3) (-)) leached from 'Tifdwarf' bermudagrass in lysimeters. Forty lysimeters were planted with 'Tifdwarf' bermudagrass, of which 20 were inoculated with B. longicaudatus and 20 were noninoculated. Root length was compared between treatments at six, 12, and 18 weeks after initiation of the experiments. Turf was fertilized every three weeks, and leaching events were simulated at 21 and 42-day intervals in trial one and trial two, respectively. Leachate was collected, and the quantity of NO(3) (-) leached was compared between treatments. Root reductions were observed in lysimeters inoculated with B. longicaudatus at all evaluation dates. Quantity of NO(3) (-) leached was greater in inoculated lysimeters at the 18-week evaluation during both trials. This study indicates that nematode damage to turf roots limits root vigor and N uptake, thereby increasing nitrate leaching, adding to water quality concerns.

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.

Alternatives to fenamiphos for management of plant-parasitic nematodes on bermudagrass.

Plant-parasitic nematodes can be very damaging to turfgrasses. The projected cancellation of the registration for fenamiphos in the near future has generated a great deal of interest in identifying acceptable alternative nematode management tactics for use on turfgrasses. Two field experiments were conducted to evaluate the effectiveness of repeated applications of several commercially available nematicides and root biostimulants for reducing population densities of plant-parasitic nematodes and (or) promoting health of bermudagrass in nematode-infested soil. One experimental site was infested with Hoplolaimus galeatus and Trichodorus obtusus, the second with Belonolaimus longicaudatus. In both trials, none of the experimental treatments reduced population densities (P

First Report of Meloidogyne partityla on Pecan in Florida.

Pecan (Carya illinoensis (Wagenh.) K. Koch) is an important tree in the southern United States for commercial nut production and residential use. Meloidogyne partityla (pecan root-knot nematode) is only known to parasitize trees in the Juglandaceae including pecan, walnut, and hickory. In the United States, it has been reported on pecan in Texas, New Mexico, and Georgia and internationally in South Africa. Portions of a large pecan nursery in Madison County, Florida were infested with an unknown species of root-knot nematode. The pecan trees at this nursery are grafted onto rootstock and grown in the field until the trees are large enough to sell as bare-root transplant stock in several states including and adjoining Florida. Trees infected by the root-knot nematodes were stunted, had extensive galling and rotting of the root system, and pulled from the ground relatively easily compared with noninfected trees. Attempts to rear these nematodes on tomato in the greenhouse were unsuccessful. Young egg-laying females were isolated directly from pecan roots for speciation. Enzymes extracted from females were resolved with polyacrylamide gel electrophoresis [4% stacking (pH 6.8) and 8% separating gel (pH 8.8) with Tris-glycine buffer]. The esterase (Est) and malate dehydrogenase (Mdh) phenotypes of the unknown Meloidogyne sp. were consistent with those reported for M. partityla. In addition, specimens of M. partityla maintained by the USDA Southeastern Fruit and Tree Nut Research Laboratory in Byron, GA were obtained and their Est and Mdh phenotypes compared with the unknown Meloidogyne sp. under identical electrophoretic and enzyme staining protocols. The Est and Mdh phenotypes of the two isolates were identical. Therefore, we conclude that the root-knot nematodes infesting the pecan nursery in Florida are M. partityla. To our knowledge, this is the first report of this nematode in Florida and also the first report of this nematode from infected nursery stock. It is unknown how long the field has been infested but clearly, there is potential for spread of M. partityla to locations around Florida and bordering states. This nematode may be widespread throughout pecan-growing regions of the United States. References: (1) K. P. N. Kleynhans. Phytophylactica 18:103, 1986. (2) A. P. Nyczepir et al. Plant Dis. 86:441, 2002. (3) J. L. Starr et al. J. Nematol. 28:565, 1996. (4) S. H. Thomas et al. Plant Dis. 85:1030, 2001.

Host Status of 'SeaIsle 1' Seashore Paspalum (Paspalum vaginatum) to Belonolaimus longicaudatus and Hoplolaimus galeatus.

Belonolaimus longicaudatus and Hoplolaimus galeatus are considered among the most damaging pathogens of turfgrasses in Florida. However, the host status of seashore paspalum (Paspalum vaginatum) is unknown. Glasshouse experiments were performed in 2002 and 2003 to determine the tolerance of 'SeaIsle 1' seashore paspalum to a population of B. longicaudatus and a population of H. galeatus, and to compare to 'Tifdwarf' bermudagrass for differences. Both nematode species reproduced well on either grass, but only B. longicaudatus consistently reduced root growth as measured by root length. Belonolaimus longicaudatus reduced root growth (P

First Report of Plant-Parasitic Nematodes on Seashore Paspalum (Paspalum vaginatum) in Florida.

Seashore paspalum (Paspalum vaginatum Swartz) is a warm-season grass capable of growing in the saline environments present in coastal areas of Florida (2). A major limitation of cultivating turfgrasses in the sandy soils of Florida is the destruction of roots by plant-parasitic nematodes (3). A survey was performed to determine the plant-parasitic nematodes associated with seashore paspalum. Sampling locations ranged from Daytona Beach to Miami Beach on the eastern coast and from Tampa to Naples on the western coast. Soil samples were taken during the spring and summer months of 2002 and 2003 from different golf courses and home lawns. In 2002, soil samples were taken from five golf courses (37 samples) and seven home lawns (17 samples). In the next year, three golf courses (23 samples) and 13 home lawns (34 samples) were sampled. Nematodes were extracted from 100 cm3 soil samples using a modified centrifugal-sugar flotation technique (1). Ten genera of plant-parasitic nematodes were present from the samples obtained from golf courses. In addition, two more plant-parasitic nematode genera were present in samples from home lawns. The genera most frequently detected were Hoplolaimus, Mesocriconema, Hemicriconemoides, and Helicotylenchus, which were found at 100, 100, 88, and 88% of the golf courses surveyed and at 75, 95, 70, and 85% of the home lawns sampled, respectively. Genera Xiphinema, Pratylenchus, and Tylenchorhynchus, were found in less than 30% of the golf courses and less than 45% of the home lawns sampled. Genera Peltamigratus and Hemicycliophora were associated with a low percentage of the home lawns. A moderately high frequency of the genus Belonolaimus present in soil samples from golf courses (50%) and home lawns (40%) was consistent for other grasses grown in sandy soils associated with coastal areas in Florida (4). Populations of the genera Belonolaimus, Hoplolaimus, Helicotylenchus, Trichodorus, Hemicriconemoides, and Mesocriconema were above the action threshold levels for bermudagrass used by the University of Florida Nematode Assay Laboratory. Genera Hoplolaimus, Belonolaimus, and Trichodorus were associated with irregular-shaped yellowing and declining turfgrass areas sampled in this survey. Large populations of Helicotylenchus spp. (>500 nematodes per 100 cm3 of soil) were often found associated with seashore paspalum. To our knowledge, this is the first report of plant-parasitic nematodes associated with seashore paspalum in Florida. References: (1) W. R. Jenkins. Plant Dis. Rep. 48:692, 1964. (2) J. Morton. Proc. Fla. State Hortic. Soc. 86:482, 1973. (3) V. G. Perry and H. Rhoades. Pages 144-149 in: Nematology in the Southern Region of the United States. Southern Cooperative Series Bull. 276, University of Arkansas Agric. Pub., Fayetteville, 1982. (4) R. T. Robbins and K. R. Barker. J. Nematol. 6:1, 1974.

Slit Injection of 1,3-Dichloropropene for Management of Belonolaimus longicaudatus on Established Bermudagrass.

Belonolaimus longicaudatus is a serious problem on bermudagrass, a common warm-season turfgrass, in Florida. The cancellation of organophosphate nematicides necessitates that new management tools be identified for use on sports turf. Postplant application of 1,3-dichloropropene (1,3-D) on bermudagrass was evaluated for management of B. longicaudatus on golf course fairways and driving ranges. A series of 10 experiments were conducted to evaluate the effectiveness of 1,3-D in reducing population densities of B. longicaudatus and enhancing bermudagrass recovery from nematode damage. In 5 of 10 experiments, 1,3-D injected at 46.8 liters/ha was effective in reducing population densities of B. longicaudatus (P < 0.05) compared to untreated plots 2 to 4 weeks after treatment. One month after treatment, population densities of B. longicaudatus ranged from 59% to 97% of those in untreated plots. Nematode suppression generally lasted 2 months or less. Turf visual performance was improved following injection with 1,3-D (P < 0.05) over untreated plots when other factors were not limiting. Turf root development also was enhanced following injection with 1,3-D. Postplant injection of 1,3-D could be a useful nematode management tool for certain sports turf applications.

Effect of sorghum-sudangrass and velvetbean cover crops on plant-parasitic nematodes associated with potato production in Florida.

In a 3-year field study, population densities of Belonolaimus longicaudatus and other plant-parasitic nematodes and crop yields were compared between potato (Solanum tuberosum) cropping systems where either sorghum-sudangrass (Sorghum bicolor x S. arundinaceum) or velvetbean (Mucuna pruriens) was grown as a summer cover crop. Population densities of B. longicaudatus, Paratrichodorus minor, Tylenchorhynchus sp., and Mesocriconema sp. increased on sorghum-sudangrass. Population densities of P. minor and Mesocriconema sp. increased on velvetbean. Sorghum-sudangrass increased population densities of B. longicaudatus and Mesocriconema sp. on a subsequent potato crop compared to velvetbean. Potato yields following velvetbean were not greater than following sorghum-sudangrass despite reductions in population densities of B. longicaudatus.

Yield Reduction and Root Damage to Cotton Induced by Belonolaimus longicaudatus.

Sting nematode (Belonolaimus longicaudatus) is recognized as a pathogen of cotton (Gossypium hirsutum), but the expected damage from a given population density of this nematode has not been determined. The objective of this study was to quantify the effects of increasing initial population densities (Pi) of B. longicaudatus on cotton yield and root mass. In a field plot study, nematicide application and cropping history were used to obtain a wide range of Pi values. Cotton yields were regressed on Pi density of B. longicaudatus to quantify yield losses in the field. In controlled environmental chambers, cotton was grown in soil infested with increasing Pi's of B. longicaudatus. After 40 days, root systems were collected, scanned on a desktop scanner, and root lengths were measured. Root lengths were regressed on inoculation density of B. longicaudatus to quantify reductions in the root systems. In the field, high Pi's (>100 nematodes/130 cm(3) of soil) reduced yields to near zero. In controlled environmental chamber studies, as few as 10 B. longicaudatus/130 cm(3) of soil caused a 39% reduction in fine cotton roots, and 60 B. longicaudatus/130 cm(3) of soil caused a 70% reduction. These results suggest that B. longicaudatus can cause significant damage to cotton at low population densities, whereas at higher densities crop failure can result.

Population Dynamics of Belonolaimus longicaudatusin a Cotton Production System.

Belonolaimus longicaudatus is a recognized pathogen of cotton (Gossypium hirsutum), but insufficient information is available on the population dynamics and economic thresholds of B. longicaudatus in cotton production. In this study, data collected from a field in Florida were used to develop models predicting population increases of B. longicaudatus on cotton and population declines under clean fallow. Population densities of B. longicaudatus increased on cotton, reaching a carrying capacity of 139 nematodes/130 cm(3) of soil, but decreased exponentially during periods of bare fallow. The model indicated that population densities should decrease each year of monocropped cotton, if an alternate host is not present between sequential cotton crops. Economic thresholds derived from published damage functions and current prices for cotton and nematicides varied from 2 to 5 B. longicaudatus/130 cm(3) of soil, depending on the nematicide used.

Effects of potato-cotton cropping systems and nematicides on plant-parasitic nematodes and crop yields.

Belonolaimus longicaudatus has been reported as damaging both potato (Solanum tuberosum) and cotton (Gossypium hirsutum). These crops are not normally grown in cropping systems together in areas where the soil is infested with B. longicaudatus. During the 1990s cotton was grown in a potato production region that was a suitable habitat for B. longicaudatus. It was not known how integrating the production of these two crops by rotation or double-cropping would affect the population densities of B. longicaudatus, other plant-parasitic nematodes common in the region, or crop yields. A 3-year field study evaluated the viability of both crops in monocropping, rotation, and double-cropping systems. Viability was evaluated using effects on population densities of plant-parasitic nematodes and yields. Rotation of cotton with potato was found to decrease population densities of B. longicaudatus and Meloidogyne incognita in comparison with continuous potato. Population densities of B. longicaudatus following double-cropping were greater than following continuous cotton. Yields of both potato and cotton in rotation were equivalent to either crop in monocropping. Yields of both crops were lower following double-cropping when nematicides were not used.