J. Earl Creech

First Report of Soybean Cyst Nematode Reproduction on Purple Deadnettle under Field Conditions

Soybean cyst nematode commonly infests soybean fields in the United States and is a threat to profitable soybean production. Purple deadnettle is common in Indiana production fields and frequently occurs at very high densities. Purple deadnettle plants were removed from a research site infested with SCN. Peadnettle roots were found to possess cysts containing eggs. The morphology of cysts and juveniles was consistent with SCN. Based on the distribution of other cyst nematodes in Indiana, a bioassay on soybean from the field, and morphometric observations, we determined the identity of the nematode to be SCN.

Survey of Broadleaf Winter Weeds in Indiana Production Fields Infested with Soybean Cyst Nematode (Heterodera Glycines)1

Fifty-five soybean cyst nematode (SCN)–infested production fields across Indiana were surveyed in March 2004 to assess broadleaf winter weed prevalence. The most frequently occurring weeds were common chickweed (87%), speedwell (83%), buttercup (58%), and henbit (53%). Henbit and wild garlic were present at the highest average densities, both occurring at greater than 50 plants/m2. Based on relative abundance indices, common chickweed and henbit were the most prevalent winter weeds in this survey. As a composite, winter weed hosts of SCN were found in 93% of fields and occurred at an average density of 151 plants/m2. No correlation existed between weed density and SCN egg counts. Frequency, uniformity, density, and diversity indices for individual weed species were generally higher in the southern region of Indiana than in the north. Thus, the region of highest risk for SCN reproduction and population increase on winter weeds in Indiana appears to be in the southern part of the state. Nomenclature: Buttercup, Ranunculus spp, common chickweed, Stellaria media (L.) Vill. #3STEME, henbit, Lamium amplexicaule L. # LAMAM, speedwell, Veronica spp, wild garlic, Allium vineale L. # ALLVI, soybean cyst nematode, Heterodera glycines Ichinohe. Additional index words: Crop rotation, integrated pest management, purple deadnettle, soil temperature, winter annual weeds. Abbreviations: GPS, Global Positioning System; GR, glyphosate-resistant.

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.

Development of Soybean Cyst Nematode on Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium Purpureum)

A survey of seven production fields in Indiana, Illinois, and Ohio was conducted to assess henbit and purple deadnettle growth and soybean cyst nematode (SCN) development and reproduction on these weeds. Autumn and spring growth of purple deadnettle and henbit was influenced by location within each state. In general, winter annual weeds were larger in size and reached maturity earlier in the spring at the southern sample sites than those in the north. All growth stages of SCN were found to be associated with henbit and purple deadnettle at both autumn and spring sample timings. SCN juveniles were generally found infecting roots at highest abundance in the spring. SCN cyst and egg production also were widespread and occurred to a much higher degree during the autumn than the spring developmental period. The results of this survey indicate that management tactics designed to minimize the potential for SCN reproduction on winter annual weeds would probably be most effective if conducted in the autumn, when the majority of SCN reproduction occurred. However, spring populations of winter annual weeds that harbor SCN juveniles might facilitate additional SCN reproduction and population increase if the weeds are not controlled in a timely manner prior to planting. Nomenclature: Henbit, Lamium amplexicaule L. LAMAM; purple deadnettle, Lamium purpureum L. LAMPU; soybean, Glycine max (L.) Merr; soybean cyst nematode, Heterodera glycines Ichinohe.

Influence of Intraspecific Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium purpureum) Competition on Soybean Cyst Nematode Reproduction

Abstract A greenhouse study was conducted to determine the effect of henbit and purple deadnettle density on weed biomass accumulation and soybean cyst nematode (SCN) reproduction. SCN did not impact shoot or root dry weight of purple deadnettle, henbit, or soybean. Foliar and root biomass of henbit and purple deadnettle were comparable but the biomass per stem was higher for purple deadnettle. Shoot and root biomass per pot of henbit and purple deadnettle at corresponding plant densities were statistically similar and were generally higher with increasing plant density. Henbit produced a greater number of stems than purple deadnettle and the least number of stems for both species existed at low densities. Purple deadnettle allowed for more SCN reproduction than did henbit. Weed densities also influenced SCN cyst and egg production but the results were species dependent. The highest SCN reproduction per pot was supported at low to moderate densities of purple deadnettle but at moderate to high densities of henbit. These results suggest that purple deadnettle should be more aggressively managed than henbit in management programs for SCN, but that henbit, especially at high densities, can support SCN reproduction at levels near those of purple deadnettle. Nomenclature: Henbit, Lamium amplexicaule L. LAMAM; purple deadnettle Lamium purpureum L. LAMPU; soybean Glycine max (L.) Merr. ‘Williams 82’ and ‘PI437654’

Sulfosulfuron effects on growth and photosynthesis of 15 range grasses

We conducted greenhouse experiments to compare photosynthetic and growth responses of 2 invasive annual grasses (downy brome = Bromus tectorum L. and medusahead = Taeniatherum caput-medusae (L.) [Nevski]), 6 caespitose grasses, and 7 rhizomatous grasses to the herbicide sulfosulfuron (1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea). Our objectives were to identify general patterns of species responsiveness and test the hypothesis that sulfosulfuron induced reduction in photosynthetic activity and shoot growth would be more pronounced in small relative to larger plants. Small plants in a spring experiment and large plants in a summer experiment were treated with sulfosulfuron (70 g ai ha -1 ). Wildryes and bromes were consistently injured; whereas, 5 of the 7 wheatgrasses were not susceptible to sulfosulfuron. Rhizomatous grasses generally experienced greater damage from sulfosulfuron than caespitose grasses. These results suggest that sulfosulfuron would provide a useful rangeland management tool to control unwanted invasive annual grasses without significantly hindering growth and physiology of desirable rangeland grasses.

Role of Winter Annual Weeds as Alternative Hosts for Soybean Cyst Nematode

Soybean cyst nematode (Heterodera glycines Ichinohe, SCN) has been reported to parasitize a broad range of host plants, encompassing nearly 150 legume and non-legume genera representing 22 plant families. Several SCN host species are common winter annual weeds in US soybean production fields and include purple deadnettle (Lamium purpureum L.), henbit (Lamium amplexicaule L.), field pennycress (Thlaspi arvense L.), shepherd’s purse [Capsella bursa-pastoris (L.) Medik], common chickweed [Stellaria media (L.) Vill.], and smallflowered bittercress (Cardamine parviflora L.). The influence of winter annual weed management on SCN population densities has received little attention to date and warrants further investigation by multidisciplinary research involving weed scientists, nematologists, and soybean production specialists. Introduction Winter annual weed populations in production fields (Fig. 1) have been increasing due to the widespread adoption of conservation tillage practices and reduced reliance on herbicides with soil residual activity (37). A number of common winter annual weed species have recently been identified as alternative hosts for soybean cyst nematode (52). SCN has long been known as a threat to profitable soybean production throughout soybean growing regions of the United States. Current management systems for SCN include rotation to a nonhost crop and use of SCN resistant soybean varieties but fail to address winter annual weed management. Failure to manage winter annual weeds may provide a niche for SCN reproduction and increase population density in the absence of soybean. The purpose of this review article is to summarize the current literature about the management implications of SCN and winter annual weed management. Fig. 1. Winter annual weeds have become more common in crop fields due to reduced reliance on tillage and soil-applied herbicides. Crop Management 1 July 2008 Conservation tillage acreage in the United States has increased steadily from an estimated 70 million acres in 1990 to over 110 million acres in 2004 (5). Reduced soil disturbance associated with these systems has created a favorable environment for winter annual weed establishment and seed production (55). The widespread adoption of glyphosate-resistant (GR) crops is another trend that may have contributed to this recent abundance of winter weeds. In 2007, GR soybean was planted on approximately 91% of the soybean production hectares in the United States (3). Because glyphosate can be applied to emerged GR soybean, many growers delay herbicide applications until after crop planting which allows the winter annuals to mature and produce seed. In addition, increased use of glyphosate postemergence in soybean has led to decreased reliance on soil-residual herbicides. Pendimethalin, imazethapyr, and imazaquin were each applied on 21 to 45% of the United States soybean acres in 1996 but only 6 to 8% of the acreage in 2006 (4). These soil-residual herbicides can suppress fall emergence of winter annual weeds when applied in the spring (7). An additional factor that may have increased the prevalence of winter annual weeds has been the relatively mild winters experienced in recent years which have enhanced the ability of winter weed seedlings to avoid winter-kill (29). Winter annual weeds can have a number of negative impacts on cropping systems. Dense populations of winter annual weeds can slow drying and warming of soil in the spring (8,19); the combination of which may lead to delayed planting dates and decreased yields (25). In conventionally-tilled fields, the presence of winter annuals can increase tillage, labor, and fuel costs required for spring seedbed preparation (8,19). These weeds can be difficult to control in no-till production systems with late spring herbicide applications because of their advanced growth stage. Similarly, winter annual weeds can interfere with crop seeding depth and crop establishment in high residue areas (29). Winter annual weeds can also host various crop pests. For example, common chickweed is a host for black cutworm (45), a common insect pest of corn. Winter annual weeds can be managed with herbicides, tillage, and/or cover crops. Although the presence of winter annuals in production fields can be problematic, operations required to remove these plants may also have negative impacts on crop production systems. Tillage can be effective for control of winter annual weeds but it has also been linked to increased risk of soil erosion and can stimulate SCN population growth (27,61). Removal of winter annual weeds with a fall applied herbicide application results in bare soil that may warm and dry faster in the spring (31). However, these conditions have been observed to promote earlier emergence and subsequent management problems of summer annual weeds, giant foxtail, giant ragweed, common lambsquarters, and common waterhemp [(62), W. G. Johnson, unpublished data]. Finally, winter cover crops have been implicated in causing yield reductions in subsequent crops (20,21,51,54). Although not actively competing with the crop, terminated cover crops can reduce N availability (21,51,54), release allelopathic compounds (26,38), and limit moisture availability (10,11,33) — all of which can inhibit the growth and yield of the subsequent crop. Soybean Cyst Nematode SCN consistently ranks as the most economically important soybean pathogen in the United States (57,58). Since it was first detected in 1954 in North Carolina, SCN has been discovered in most US soybean production states and is especially common in Indiana where it currently infests at least 82 of 92 counties (22). Soybean yield losses within fields infested with SCN can range from 5% to 95% depending upon severity of infestation, soil type, soybean variety, weather conditions, and presence of other soybean pests (e.g., weeds, insects, and fungal pathogens) (43,44). The life cycle of SCN begins inside the mature female with the fertilized egg. Following embryogenesis and a molt, the second-stage juvenile (J2) emerges from the egg and moves through the soil in search of a suitable host. Once the root is located, the J2 uses its stylet to pierce the cells adjacent to the vascular cylinder and to induce the formation of a specialized feeding site called a syncytium (28). The juvenile, now sedentary, draws nutrients and materials Crop Management 1 July 2008 from the plant root for its growth and development and undergoes three additional molts before adulthood is reached (60). The syncytium of the male degenerates, signaling an end to the feeding period, and the wormlike adult becomes mobilized and exits the root. The female, on the other hand, remains immobile and continues to feed. As its body continues to swell, the female eventually breaks through the surface of the root but remains attached to the feeding site. An SCN female generally produces between 40 to 600 eggs on average (46). Upon death, the females’ body becomes a tough, protective covering (called a “cyst”) that protects the eggs from desiccation and predation by microbes until favorable conditions arrive for hatch. Eggs can remain viable within a cyst for several years. On its own, SCN can move only a few centimeters in the soil in its lifetime. However, cysts can travel long distances by tillage and harvest equipment, wind, water, contaminated seed, and animals (35). SCN development and reproduction are dependent on several factors, including soil temperature, moisture, texture, and pH (1,47,50,60). Soil temperature is of particular importance in the relationship between SCN and winter annual weed hosts. The optimal temperature for SCN development is 77° F (1) but higher or lower temperatures can slow SCN development (47). The time required for a second generation of SCN to be produced can range from 24 days at 73°F to 40 days at 64°F (56). Alston and Schmitt (1) reported that the time SCN takes to complete a lifecycle is influenced by the season. SCN required four weeks and 534 ± 24 degree days between 41 and 86°F (DD41/86) during June and July. However, from July to August it took SCN three weeks and 429 ± 24 DD41/86. During September and October four weeks were once again required to complete a lifecycle, and 372 ± 33 DD41/86 were needed. Weather station data from Indiana indicate that the period of overlap of high SCN activity and winter annual weed growth may be limited to a few weeks in early fall and late spring when soil temperatures favor both nematode activity and weed growth (6,42). These data suggest that soil temperatures in Indiana may be adequate for SCN to complete a life cycle in the fall and/or spring on compatible winter annual weeds when soybean is not present in the field and was recently confirmed by Creech et al. (12) (Fig. 2). Fig. 2. Optimal conditions for SCN growth in relationship to soybean and winter annual weed growth. Weeds as Alternative Hosts of SCN SCN has a relatively broad host range, but its only major agronomic crop host is soybean. Riggs (41) reviewed the literature and compiled a list of 96 genera of Fabaceae (Leguminosae) and 50 non-legume genera representing 22 plant families that have been reported as alternative hosts of SCN. Several SCN host species are common winter annual weeds in Indiana. In a recent Crop Management 1 July 2008 greenhouse experiment in Ohio, purple deadnettle (Lamium purpureum L.) (Fig. 3), henbit (Lamium amplexicaule L.) (Fig. 4), field pennycress (Thlaspi arvense L.) (Fig. 5), and shepherd’s-purse [Capsella bursa-pastoris (L.) Medik] (Fig. 6) were shown to support SCN reproduction (52). Earlier reports had identified common chickweed [Stellaria media (L.) Vill.] (Fig. 7) and smallflowered bittercress (Cardamine parviflora L.) (Fig. 8) as hosts to SCN (41). In addition, Creech et al. (12,17) has shown that SCN can reproduce on purple deadnettle and henbit in the field after soybean harvest in the fall in Indiana. F

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

Survey of Indiana Producers and Crop Advisors: A Perspective on Winter Annual Weeds and Soybean Cyst Nematode (Heterodera glycines)

Growers and certified crop advisors (CCAs) across Indiana were surveyed during the winter of 2003 to 2004 to assess their perceptions about soybean cyst nematode (SCN) and use of SCN management practices. Most farmers (57%) and CCAs (72%) surveyed reported a moderate to high level of concern regarding SCN and its potential impact on soybean yield. The majority of those surveyed were also aware that some winter annual weeds can serve as hosts for SCN. Crop management practices specifically aimed at managing the impact of SCN were employed by 55 and 78% of growers and CCAs, respectively. However, only 21% percent of growers said that they had sampled a field for nematodes within the last two years. Growers from eastern and southern Indiana were less likely to be concerned about SCN, to implement SCN management strategies, and to have the soil tested for SCN than growers throughout the rest of the state. In addition, smaller farmers appear to be less concerned and knowledgeable about SCN than those who operate larger farms. The results of this survey suggest that the majority of Indiana growers would likely adopt winter weed control to manage SCN. Also, with respect to winter weed control, future Extension efforts should be focused on southern Indiana where both the risk for SCN reproduction on winter annuals and the need for education on SCN appear to be highest. Nomenclature: Soybean, Glycine max (L.) Merr; 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.