Ronald B. Hammond

Genetic linkage mapping of the soybean aphid resistance gene in PI 243540

The soybean aphid (Aphis glycines Matsumura) is a pest of soybean [Glycine max (L.) Merr.] in many soybean growing countries of the world, mainly in Asia and North America. A single dominant gene in PI 243540 confers resistance to the soybean aphid. The objectives of this study were to identify simple sequence repeat (SSR) markers closely linked to the gene in PI 243540 and to position the gene on the consensus soybean genetic map. One hundred eighty-four F2 plants and their F2:3 families from a cross between the susceptible cultivar Wyandot and PI 243540, and the two parental lines were screened with the Ohio biotype of soybean aphid using greenhouse choice tests. A SSR marker from each 10-cM section of the consensus soybean map was selected for bulked segregant analysis (BSA) to identify the tentative genomic location of the gene. The BSA technique was useful to localize the gene to a genomic region in soybean linkage group (LG) F. The entire F2 population was then screened with polymorphic SSR markers from this genomic region and a linkage map with nine SSR markers flanking the gene was constructed. The aphid resistance gene was positioned in the interval between SSR markers Satt334 and Sct_033 on LG F. These SSR markers will be useful for marker assisted selection of this gene. The aphid resistance gene from PI 243540 mapped to a different linkage group than the only named soybean aphid resistance gene, Rag1, from ‘Dowling’. Also, the responses of the two known biotypes of the soybean aphid to the gene from PI 243540 and Rag1 were different. Thus, the aphid resistance gene from PI 243540 was determined to be a new and independent gene that has been named Rag2.

Susceptibility of North American Native and Non-native Slugs (Mollusca: Gastropoda) to Phasmarhabditis hermaphrodita (Nematoda: Rhabditidae)

Phasmarhabditis hermaphrodita caused significant mortality of the two native species, Deroceras laeve and Leidyula floridana, and of one introduced species D. reticulatum, but not of the other three introduced species, Arion hortensis, A. subfuscus and Limax maximus. Even the juvenile stages of A. subfuscus and L. maximus showed no mortality in nematode treatments. However, treatments with nematodes resulted in rapid and strong feeding inhibition in all six species. Surviving slugs resumed feeding when fresh food was provided. This study expands the host range of P. hermaphrodita to include a new family Vaginulidae and demonstrates the inability of P. hermaphrodita to cause mortality of A. hortensis, A. subfuscus and L. maximus. These three species use feeding suspension as an evasive behavior to escape nematode infection.

DETERMINING THE INFLUENCE OF SPRAY QUALITY, NOZZLE TYPE, SPRAY VOLUME, AND AIR-ASSISTED APPLICATION STRATEGIES ON DEPOSITION OF PESTICIDES IN SOYBEAN CANOPY

Field studies were established in north central Ohio to determine the effect of different application strategies on targeting of foliar pesticides in narrow-row (18 cm) soybeans. Several different application factors were tested, including spray quality, nozzle type, air-assistance, and spray volume. In 2005, the spray mix included a fungicide. In 2006, in addition to the fungicide, an insecticide was included. Plant samples were removed from each test plot, and stems and leaves from the bottom third and middle third of the plant were separated for analysis. Overall, there was significantly less active ingredient found in the lower third of the canopies than the middle third, and significantly less pesticide residue was found on stems than leaves from the same canopy location. Significantly more fungicide residue was found on lower leaves treated by the medium-quality XR8004 flat-fan nozzle in 2005 than the coarse-quality XR8005 flat-fan nozzle. There were no differences in fungicide residue found on middle canopy leaves between the fine, medium, and coarse quality flat-fan nozzles. The twin-fan pattern nozzles (Turbo Duo and TwinJet) produced the lowest amounts of fungicide residue on the lower leaves in 2005. The mechanical canopy opener produced significantly higher fungicide residues on middle canopy leaves than all other treatments. The Jacto air-assist sprayer using JA3 hollow-cone nozzles produced the highest fungicide residues on lower canopy leaves in 2005. There were some statistical differences between the amounts of fungicide and insecticide residue found on plant tissue in 2006 because of the high amount of variability in the sample data. Overall in 2006, the higher volume XR8004 treatment (187 L ha -1 ) and the twin-fan TTJ60-11003 treatment at 145 L ha -1 performed similar to the Jacto sprayer making applications at 145 L ha -1 using either flat-fan or hollow-cone nozzles. In general, higher volume applications produced higher amounts of fungicide and insecticide residue on leaves from the middle of the canopy for conventional flat-fan and air-assist applications. Spray volume had less affect on residues measured on leaves from the lower canopy area. Across two years of different canopies at the same spray volume (145 L ha -1 ), the Jacto sprayer using JA3 hollow-cone nozzles produced more fungicide residue on middle canopy stems and lower canopy leaves than the medium-quality XR8004 flat-fan nozzle.

Interaction of planting times following the incorporation of a living, green cover crop and control measures on seedcorn maggot populations in soybean

Abstract The impact of delaying soybean [ Glycine max (L.) Merr.] planting following the incorporation of a living, green cover crop and using various insecticide management practices on seedcorn maggot [ Delia platura (Meigen)] populations was evaluated. Phorate soil insecticide in a 15.8 cm band and Agrox D-L Plus seed treatment [a mixture of diazinon (0.33% w/w), lindane (15.0% w/w), and captan (14.67% w/w) were applied at planting immediately after, and 1.5 or 3 weeks after, cover crop incorporation that occurred in early May. Seedcorn maggots were sampled with adult emergence traps, and subsequent soybean injury to plumules was estimated. The number of days following tillage that soybean was planted had little effect on maggot numbers collected, but injury was lowest on soybean planted 3.5 weeks after incorporation of the cover crop. Thermal unit accumulations indicated that seedcorn maggot oviposition occurred at the time of tillage, and that the majority of insects were nearing or entering the non-feeding pupal stage at the time of the last planting, resulting in less plant injury. Phorate treatments provided the largest reduction of maggot numbers. Plant injury was least, however, when soybean was protected by an Agrox seed treatment, especially when the seed and the Agrox were mixed in a bucket before use. These reductions were observed at all three planting times, although the percentage reduction from the control differed among the three planting dates. When spring tillage incorporates a green, living organic matter into the soil in the spring, plant injury can be reduced if a grower waits for 2.5–3 weeks after tillage until planting, when ∼250 thermal units (base of 3.9°C) are accumulated and the majority of insects are in the pupal stage. If planting is done immediately or shortly after tillage, it is recommended that soybean seed be protected with a seed treatment, preferably one that ensures complete coverage of the seed.

Field Resistance of Two Soybean Germplasm Lines, HC95–15MB and HC95–24MB, Against Bean Leaf Beetle (Coleoptera: Chrysomelidae), Western Corn Rootworm (Coleoptera: Chrysomelidae), and Japanese Beetles (Coleoptera: Scarabaidae)

Abstract Two recently released, Mexican bean beetle, Epilachna varivestis, Mulsant, resistant soybean, Glycine max (L.) Merrill, germplasm lines, HC95–15MB and HC95–24MB, were examined for foliar and pod feeding resistance to adult bean leaf beetles, Cerotoma trifurcata (Förster), western corn rootworms, Diabrotica virgifera virgifera LeConte, and Japanese beetles, Popillia japonica Newman. Both lines were planted along with a susceptible control cultivar in 18 by 30-m plots and separate 0.8-ha size fields. Insects were sampled on a weekly basis with a sweep net. In late summer, defoliation ratings were recorded along with data on percentage pod feeding. Although a few significant differences in insect densities were obtained among the soybean lines on some sampling dates, no specific trends were observed in the ability of the resistant germplasm to reduce insect numbers. Insect population densities were similarly on all lines. However, both resistant lines were able to reduce defoliation during the growing season. Conversely, percentage pod feeding was similar among all the soybean lines, with no differences observed. The resistant germplasm lines appear able to lower levels of defoliation, and thus, offer a potential management tactic where leaf feeding, i.e., defoliation, is of concern. However, their ability to greatly reduce beetle population densities, and for the bean leaf beetle, to reduce pod feeding, appears limited.

Long-term conservation tillage studies: impact of no-till on seedcorn maggot (Diptera: Anthomyiidae)

Abstract A long-term study (12 years) was conducted to determine the feasibility of growing soybean in rotation with corn on the hill land of southeastern Ohio, USA, using conservation tillage practices that included investigating the effect of tillage on populations of seedcorn maggot, Delia platura Meigen. Corn and soybean were grown using various management and conservation tillage practices including no-till, paraplow, and chisel plow, multiple diskings, and conventional tillage. Adult seedcorn maggots were sampled over a 12-year period to assess the impact of tillage practice on population density. No-till and paraplow, where there was little soil disturbance, generally had fewest adults. Chisel plowing caused a slight increase in numbers of adults, although densities were never as high as plowing and/or disking treatments. The largest number of adults were collected from areas where soil was disturbed, either by plowing and disking or by multiple diskings. This study presents evidence that no-till systems do not enhance seedcorn maggot populations and indicates that population increases are associated with tillage systems involving substantial soil disturbance.

Simulated Insect Defoliation on Soybean: Influence of Row Width

Abstract An ongoing change in soybean production gaining popularity in the United States is a reduction in row spacing. Plant canopy closure is quicker and leaf area index is greater, thus yield is usually higher. Because yield response to insect defoliation is primarily a function of how defoliation causes changes in light interception, the possibility exists that the insect-injury–yield-loss relationship might differ among row widths. Soybean was grown in four states using similar methodologies. Insect defoliation was simulated by picking leaflets based on an insect defoliation model. Plant growth measurements were taken immediately following the end of defoliation. Numerous independent variables were measured or calculated, including percentage light interception, leaf area index, percentage defoliation, and leaf area per plot. Analyses of covariance were conducted on the resultant data to determine whether insect-injury–yield-loss relationships interact with row width. A significant interaction would indicate that the impact of the variables on yield was dependent on the row width, whereas a nonsignificant interaction would suggest that the relationship between the variables and yield is similar at all row widths. Few significant interactions were obtained, indicating that the impact of the variables on yield is similar across row widths. Because of the lack of significant interactions, the insect-injury–yield-loss relationships previously developed should be usable across varying row widths. Thus, treatment decisions based on light interception and leaf area indices, both considered more appropriated measures of insect injury, should be applicable for all row spacings.

Density of potato leafhopper (Homoptera : Cicadellidae) in response to soybean-wheat cropping systems

Abstract Effects of vegetational diversity upon abundance of potato leafhopper, Empoasca fabae (Harris), were examined in four agroecosystems. One of the four cropping systems was a soybean monoculture; the other three were relay intercropping systems that varied in the amount of wheat, Triticum aestivum L. (a nonhost plant), planted between soybean rows. Each employed the same planting density and dispersion of a potato leafhopper host plant, soybean, Glycine max (L.) Merrill. The cropping systems formed a gradient of vegetational diversity of host/nonhost plant density. Soybean and wheat were co-present in experimental plots early in the season; following the wheat harvest, all four cropping systems were soybean monocultures. Preceding the wheat harvest, potato leafhoppers were substantially and significantly more abundant in the monoculture than in any of the intercropping systems. Leafhopper densities were extremely low in all the intercropping systems. After the wheat harvest, differences between the monoculture and intercropping systems gradually decreased, and fewer collection dates showed significant differences. Females and males had similar population dynamics and differences among cropping systems. No significant differences in abundance were found among the intercropping systems. Results suggest that the use of host/nonhost intercropping systems would provide growers with an alternative management tactic against potato leafhoppers.

Simulation of moderate levels of slug injury to soybean.

Abstract Slugs became a significant problem in soybean, Glycine max (L.) Merrill, in the eastern USA cornbelt as growers adopted conservation tillage production practices. Little information is known about the consequences from slug injury on soybean growth and yield. This study examined the effects of moderate levels of simulated slug injury, i.e., stand loss and defoliation to the unifoliate and 1st trifoliate leaflets, to the crop. Soybean stands were established at levels at and above those requiring replanting, and defoliation was done by removing 50% of the unifoliate and 1st trifoliate leaflets. Plant growth measurements were taken during the summer and yields recorded. The greatest impact on yield was from reduced plant stands, with 50% defoliation of the unifoliate leaflet having a much lesser impact. There was little effect from injury to the 1st trifoliate. Results suggest that growers should be most concerned when slug injury causes reduced stands and from defoliation to the unifoliate leaflet. Early planting that allows for maximum growth of the plant before slugs become active in later spring would lower the potential for economic losses.

Timing of plowing and planting: Effects on seedcorn maggot populations in soybean

Seedcorn maggots (Delia platura Meigen) are occasional pests of corn and soybean, especially in the Midwest region of the USA. A 2-year field study demonstrated that the presence and emergence of adult seedcorn maggots were governed by timing of tillage operations. Two distinct seedcorn maggot cohorts were recorded each year, one following an early plowing and another after a late plowing. Peak emergence of adult flies occurred following the accumulation of ca 408 thermal units. Similar trends in adult emergence were observed from plots with and without soybeans. A large population of seedcorn maggots during the second year reduced plant stand, but no seed yield differences were obtained.