Agronomic SCN Management Handbook An introduction to SCN and the actions you can take to reduce the costly damage.

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42˚

43˚

44˚

SCN eggs/100g of soil

1-500501-20002001-40004000+

Shows SCN presence in Ontario based on 273 samplesFigure 1. Shows SCN presence in Ontario based on 273 samples.

Agronomic SCN Management Handbook

For more information, visit SyngentaFarm.ca, contact our Customer Interaction Centre at 1-87-SYNGENTA (1-877-964-3682) or follow @syngentacanada on Twitter and tweet us your questions using #AskSYN.

“ …the most common SCN losses are not obvious enough to be visible from above-ground symptoms.”3

Source: Syngenta Canada 2015

How serious is SCN?This Agronomic SCN Management Handbook is designed as a brief introduction to soybean cyst nematode (SCN) and the actions you can take toward its management. In Canada, SCN is spreading in soybean growing areas. In the U.S., extension nematologists and plant pathologists estimate that SCN robs more yield annually than the next five soybean pathogens combined, with an estimated $1.5 billion in annual soybean yield losses.1

According to the University of Illinois, SCN can lead to losses up to 80 percent.2 However, the most common SCN losses are not obvious enough to be visible from above-ground symptoms. This means your soybean yields may be reduced by SCN while you’re not even aware of it. It is not uncommon for SCN to reduce yields by up to 40 percent without any visible above-ground symptoms.4 What’s more, SCN symptoms are often confused with other common problems such as nutrient deficiencies, chemical injury, soil compaction, drought, flooding or root rots.5 Once SCN is introduced into a field, it can never be eradicated – when you have it once, you have it forever. Because of that, it is a pest that must be managed; otherwise, it will eventually become a significant problem. Your losses associated with SCN in any given year will be directly dependent on environmental factors beyond your control, such as drought or other natural events. However, through planning and use of SCN management strategies, you can reduce the impact of these SCN-related losses.6

Since it was first identified in Ontario in 1988, SCN has been identified in most counties west of Toronto and more recently in parts of Eastern Ontario (see Figure 1).7 Unfortunately, as with other soybean production areas around the world, SCN does not stop moving and will eventually spread to all soybean production areas of Ontario.7 Dramatic yield losses from SCN will continue to trend upwards in the coming years.

SCN biologyWhat is SCN? SCN are microscopic roundworms that invade and parasitize soybean roots. There are three major life cycle stages of SCN: egg, juvenile and adult. The egg is the overwintering SCN stage that hatches as a juvenile roundworm and is attracted to the young, developing root within days of soybean seed germination (see Figures 2–3).

SCN juveniles enter the soybean root and move toward the vascular tissue, which transports moisture and nutrients throughout plant. Here they modify plant cells and begin to feed by drawing nutrients from and damaging their host. SCN continues to feed within the root but eventually the juveniles become male or female. The males exit the root tissue while the female remains and grows large enough to burst from within the root while they continue to feed, with the largest portion of the developing body exposed on the root exterior (see Figure 4).8

The young, exposed, developing female is initially white in color but becomes yellow to brown with age. Following fertilization, the female produces up to 200–500 eggs. As her life cycle is completed, the female dies and her body changes from yellow to brown. At the same time, some mature SCN eggs begin the life cycle once again, depending on environment (see Figure 5).8 The female body following death becomes the familiar “cyst” structure, which can act as a long-term, resilient casing that overwinters and can last for years. SCN is more likely to resist control measures because the many different hatch periods spread across time increase the chances of successful life cycle completion.3

SCN can complete up to six generations based primarily on the following (in no particular order):6

• Planting date • Soil temperature • Host suitability • Geographic location • Presence of alternative hosts • Length of growing season

During the soybean growing season, the most typical SCN life cycle can be completed in 24–30 days, based largely on environmental conditions such as temperature and moisture levels. Cooler temperatures and adequate moisture enhance reproduction.

Figure 2. Soybean cyst nematode egg

SCN eggs with juveniles ready to hatch

Figure 3. Soybean cyst nematode juvenile

Figure 4. Soybean cyst nematode adult female

Figure 5. Soybean cyst nematode life cycle

adult female

adult male

developingjuvenile

penetratingjuvenilehatching

juvenile

unhatched juvenile in egg

egg

cyst

soybeanroot

How SCN reduces yield SCN reduces soybean performance and yield in several ways. The primary means is the direct effect of the SCN juveniles establishing themselves within the root and the associated vascular plant tissue disruption. As the juveniles develop into full-grown adults, the efficiency of moisture and nutrient transport within the infected plant is drastically affected. Secondary effects of SCN infection include:

• Stunting and damage of developing soybean root system

• Reduction of nitrogen-fixing Rhizobium bacteria root nodules

• Disease introduction through SCN entry points within the root

• Stress interactions with any number of pests which flare within stressed soybeans

Young, developing roots are stunted when infected by SCN. These young roots do not reach their genetic maximum potential for root expression, and early

infection is often the most significant potential season-long effect on soybean performance. So not only is root area reduced on infected plants, but the existing root area is not as efficient in foraging the root zone for much-needed moisture and nutrients due to the disrupted internal vascular tissue damage from SCN. These two effects combined are predictably among the most significant to soybean yield reduction.

A reduction of nitrogen-fixation caused by SCN reducing Rhizobium bacteria efficiency also leads to reduced yield potential. As SCN enters plant roots, it promotes the secondary effect of an increase in root-attacking pathogen infection. One example of this is Fusarium virguliforme, the causal organism of Sudden Death Syndrome (SDS). This disease is often closely associated with SCN. Other diseases associated with SCN are brown stem rot, Pythium, Phytophthora and Iron Deficiency Chlorosis (IDC).

Agronomic SCN Management Handbook

Source: Iowa State University

Source: Iowa State University

Source: Iowa State University

Source: Iowa State University

SCN managementAlthough SCN can have drastic effects on soybean yield, there are management strategies you can take that have predictably positive results over time. These include:

• SCN soil sampling every 3–5 years • Weed management • Rotation with non-host crops • Use of SCN-resistant soybean varieties • Rotation of SCN-resistant sources • Use of seed-applied nematicides

To use a sports analogy, would you play an entire round of golf using only one club if you had other clubs available that could improve your game? In the same way, there are several tools available to the soybean grower that, when combined, provide improved performance in an SCN environment.

Soil sampling Initially, SCN soil sampling is recommended to provide a baseline. Then, a regular soil sampling program once every 3–5 years will provide you with a picture of whether your management practices are producing the desired result. Soil sampling is reported to be the most reliable means of confirming and monitoring SCN levels.9 However, due to the irregular distribution of SCN in a field, the SCN count from a soil sample could be misrepresenting the SCN pressure in that field. Therefore, it’s best to use soil sampling as a means to confirm presence of SCN and changes in SCN pressure over multiple years, rather than an accurate estimation of SCN pressure and possible action threshold. Specific soil sampling guidelines are available from your local, private or university nematode laboratory.

Weed management Soybeans are not the only host for SCN. An Indiana agricultural field survey determined that known SCN-host winter weeds were present in 93 percent of surveyed fields.10 According to Purdue University Extension, there are six known winter weeds that allow various levels of successful SCN reproduction:11

• Purple deadnettle (strong host) • Henbit (strong host) • Field pennycress (moderate host) • Shepherd’s purse (weak host) • Small-flowered bittercrest (weak host) • Common chickweed (weak host)

Scientists at Purdue report from their greenhouse studies that purple deadnettle and henbit are such strong alternative hosts that they support similar levels of SCN reproduction as SCN-susceptible soybeans.11

Controlling these six weeds should be an important goal within any farm’s SCN management program.

Rotation with non-host crops Non-host crop rotation is a foundational principle in managing SCN. Use of non-host crops provides the unique opportunity to reduce field-wide SCN numbers by disturbing the SCN life cycle.

Use of SCN-resistant soybean varieties If SCN is present and you plan to plant soybeans, SCN-resistant varieties are strongly recommended. SCN-resistant varieties reduce the ability of SCN to successfully colonize the soybean root, leading to a reduction of the SCN reproduction rate. If susceptible soybean varieties are used in SCN environments, predictable increases in SCN levels will occur. Since SCN has multiple generations per growing season, the more you grow SCN-susceptible soybeans in the presence of SCN, the greater the risk of SCN exploding into a significant yield-limiting pest. Also keep in mind when selecting SCN-resistant varieties that they are not all created equal. Seed companies provide tolerance scores on the degree to which their varieties are able to limit reproduction by SCN based on testing on their own selection of SCN populations. Universities might offer additional data on variety resistance, but the only true testing of the effectiveness of genetic resistance is to plant them in your fields.

The genetic sources for SCN resistance are very limited and not all have acceptable agronomic or seed quality traits, and are not often used in commercial plant breeding programs. Due to this limited pool of genetic SCN resistance, one source of commercially acceptable SCN resistance, designated as Plant Introduction 88788 (PI 88788), has been very heavily relied upon across the industry.

PI 88788, introduced in the 1980s, is the SCN resistance source for the majority of SCN-resistant varieties offered for sale across all seed soybean companies. Unfortunately, this heavy reliance on a single source of SCN resistance has led to the SCN population adapting to PI 88788 so that it no longer offers the SCN protection it once did. Multiple universities have published research on SCN populations in their state adapting to PI 88788 and increasing their reproduction on varieties using that source of resistance. Because of this, it is often recommended that you attempt to purchase non-PI 88788-sourced SCN-resistant soybeans in an effort to rotate SCN resistance sources and help manage this continued decline in SCN resistance.

For more information, visit SyngentaFarm.ca, contact our Customer Interaction Centre at 1-87-SYNGENTA (1-877-964-3682) or follow @syngentacanada on Twitter and tweet us your questions using #AskSYN.Always read and follow label directions. Cruiser Maxx Vibrance Beans is an on-seed application of Cruiser Maxx Beans Seed Treatment insecticide/fungicide and Vibrance 500 FS Seed Treatment fungicide. Vibrance Maxx is an on-seed application of: (i) Vibrance 500FS Seed Treatment fungicide; and (ii) Apron Maxx RTA Seed Treatment Fungicide or Apron Maxx RFC Seed Treatment Fungicide. Soybean seeds treated with thiamethoxam are classified as a Class 12 pesticide in Ontario. Soybean seeds which are not Class 12 pesticides are also available for sale from Syngenta. Clariva™, Cruiser Maxx®, Vibrance® and the Syngenta logo are trademarks of a Syngenta Group Company. © 2015 Syngenta.

1 Wrather, J.A., T.R. Anderson, D.M. Arsyad, J. Gai, L.D. Ploper, A. Porta-puglia, H.H. Ram and J.T. Yorinori. 1997. Soybean disease loss estimates for the top 10 soybean producing countries in 1994. Plant Dis. 81:107-110. 2 University of Illinois. Report on Plant Disease. RPD 501. 3 Schmitt, D.P., J.A. Wrather and R.D. Riggs. 2004. Biology and management of soybean cyst nematode. 2nd Edition. Schmitt & Associates of Marceline. 4 Pedersen, P. Managing Soybean Cyst Nematode. Iowa State University 5 Ontario Soil and Crop Improvement Association. 2006. SCN Detection in Non-Infested Counties of Ontario. Crop Advances: Field Crop Reports. 6 Niblack, T.L. and G.L. Tylka. SCN Management Guide 5th Edition. Plant Health Initiative – A North Central Soybean Research Program. 7 Ontario Ministry of Agriculture, Food and Rural Affairs. 2009. Diseases of Field Crops: Soybean Diseases. OMFRA Publication 811: Agronomy Guide for Field Crops. 8 Tylka, G. L. 2012. Soybean cyst nematode field guide 2nd Edition – Iowa State University Extension and Outreach. 9 Faghihi, J., and V. R. Ferris. 2006. Soybean cyst nematode. Department of Entomology. Purdue University. 10 Creech, J. E., and W. G. Johnson. 2006. Survey of broadleaf winter weeds in Indiana production fields infested with soybean cyst nematode (Heterodera glycines). Weed Technol. 20:1066-1075. 11 Mock V.A., J.E. Creech, B. Johnson, J. Faghihi, V.R. Ferris, A. Westphal and K. Bradley. 2007. Winter annual weeds and soybean cyst nematode management. Purdue University Extension bulletin WS-36.

Agronomic SCN Management Handbook

For more information, visit SyngentaFarm.ca, contact our Customer Interaction Centre at 1-87-SYNGENTA (1-877-964-3682) or follow @syngentacanada on Twitter and tweet us your questions using #AskSYN.

Protect against SCN with seed-applied nematicidesSyngenta offers ClarivaTM pn seed treatment, which provides season-long control of all SCN populations. Growers have the flexibility to choose either Clariva pn with Vibrance® Maxx seed treatment or Clariva pn with Cruiser Maxx® Vibrance® Beans seed treatment for broad-spectrum early-season insect and disease protection.

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