Judith B. Santini

Depth distribution of Rotylenchulus reniformis under crops of different host status and after fumigation

Population densities of Rotylenchulus reniformis were investigated in 15 cm horizons from the surface to 120 cm deep in field plots under fallow, grain sorghum (cv. Asgrow 571), and susceptible (cv. DP6880RR) or resistant (cv. HY798) soybean. In 2000, population densities were monitored in non-fumigated plots and in plots fumigated pre-season with 1,3-dichloropropene (1,3-D) at 38 cm depth. Fallow, grain sorghum and resistant soybean reduced the incidence of R. reniformis down to 120 cm in comparison to susceptible soybean. In 2001, population densities were monitored under cotton in these plots and in additional plots that had grown susceptible soybean cv. Vernal or resistant cv. Padre in 2000 and that were fumigated before the 2001 crop with 1,3-D at depths of 0-60, 60-120, or 0-120 cm. In 2000 non-fumigated plots, cotton fibre yields were increased by an average 35% after fallow, grain sorghum or resistant soybean compared to those after susceptible soybean. In the 2000 fumigated plots, cotton fibre yields were increased 38% after grain sorghum and resistant soybean compared to those after susceptible soybean or fallow. In plots cropped previously to susceptible soybean, fumigation at 60-120 cm deep increased cotton fibre yields by 68% compared to the non-fumigated control. Population densities in the 0-120 cm horizon were a more accurate predictor of plant damage than those at 0-30 cm. The value of R. reniformis resistant soybean cultivar-cotton crop sequences was confirmed and the importance of their effects on deep-occurring populations of R. reniformis demonstrated.

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera Glycines) and Winter Annual Weeds

Abstract Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soybean and soybean-corn) and six winter annual weed management systems (a nontreated control, fall and spring herbicide applications, spring-applied herbicide, fall-applied herbicide, fall-seeded annual ryegrass, and fall-seeded winter wheat) were evaluated in no-tillage systems from fall 2003 to 2006 at West Lafayette, IN and Vincennes, IN. Fall or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems but remained constant in the herbicide systems. Averaged over sites and years, winter annual weed densities were nearly 45% lower in the spring than the fall due to winter mortality. Corn yield was reduced by the cover crops at West Lafayette but not Vincennes. Winter annual weed management system had no influence on soybean yield. SCN population density was reduced by including corn in the crop sequence but was not influenced by winter annual weed management. The density of weedy host species of SCN in the experimental area was relatively low (less than 75 plants m−2) compared to densities that can be observed in production fields. The results of these experiments suggest that inclusion of corn into a cropping sequence is a much more valuable SCN management tool than winter annual weed management. In addition, control of winter annual weeds, specifically for SCN management, may not be warranted in fields with low weed density. Nomenclature: Soybean cyst nematode, Heterodera glycines Ichinohe; corn, Zea mays L.; soybean, Glycine max (L.) Merr; wheat, Triticum aestivum L.

Purple Deadnettle (Lamium purpureum) and Soybean Cyst Nematode Response to Cold Temperature Regimes

Abstract An experiment was conducted in growth chambers to determine the influence of cold temperature regimes, designed to simulate winter temperature conditions and spring recovery, on the interaction between purple deadnettle and soybean cyst nematode (SCN). The study was a factorial arrangement of treatments with five levels of temperature (20, 15, 10, 5, or 0 C), two levels of exposure time to the temperature (10 or 20 d), and two levels of recovery time at 20 C following exposure (0 or 20 d). In general, purple deadnettle shoot and root growth increased with temperature and time. The ability of purple deadnettle to recover from cold temperatures declined as the length of time that the plant was subjected to the cold temperature increased. SCN juveniles per gram of root at the conclusion of the temperature treatment declined as the temperature increased from 0 to 15 C, likely a result of continued purple deadnettle root growth and the inhibition of SCN hatch, growth, or development at those temperatures. SCN female, cyst, and egg production per gram of root generally increased with temperature and occurred under all temperature regimes. The results of this research indicate that, after hatching, SCN juveniles can survive a period of cold temperature inside the roots of a winter annual and continue development when transferred to warmer temperatures. Therefore, in a field environment, where fall or spring alone may not be sufficient for SCN to complete a reproductive cycle on a winter annual weed, the nematode may be able to reproduce by combining the fall and spring developmental periods. Nomenclature: Purple deadnettle, Lamium purpureum L. LAMPU; soybean cyst nematode Heterodera glycines Ichinohe

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera glycines) and Winter Annual Weeds: Years Four and Five

Abstract Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations by such species are common in no-till production fields in the midwestern United States of Indiana, Ohio, and Illinois. The objective of this research was to determine the influence of crop rotation and winter annual weed management on winter weed growth, SCN population density, and crop yield. Two crop rotations (SS and soybean–corn rotation) and six winter annual weed-management systems (autumn-applied herbicide, spring-applied herbicide, autumn + spring applied herbicides, autumn-seeded Italian ryegrass, autumn-seeded wheat, and a nontreated check) were evaluated in long-term, no-tillage systems at West Lafayette, IN, and Vincennes, IN. In the fourth and fifth years of these experiments, the 2-yr corn–soybean rotation generally resulted in increased soybean yield, decreased winter annual weed growth, and reduced SCN population density compared with SS. Autumn or spring herbicide applications or both were a more effective option than cover crops at reducing winter annual weed density. Cover-crop systems generally did not differ from the nontreated check in winter weed density. Between years three and five, winter annual weed SCN hosts in nontreated check plots increased approximately threefold to levels as high as 102 and 245 plants m−2 at West Lafayette, IN, and Vincennes, IN, respectively, which are infestation levels at or above those commonly observed in production fields. However, controlling winter annual weeds did not influence crop yields or SCN population density. The results of these studies suggest that winter weed management, even at the high levels of weed infestation present in these studies, appears to have little value as a tool for SCN management in corn and soybean production systems in the midwestern United States. Nomenclature: Soybean cyst nematode, Heterodera glycines Ichinohe; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.