Over the last 25 years, US average corn yields have increased by 1.6% per year while soybeans have only achieved a 1.27% per year gain. One reason for this discrepancy is likely the ever-increasing challenges to soybean production from soybean pests such as soybean cyst nematode, sudden death syndrome, brown stem rot, white mold, soybean aphid and bean leaf beetle. A previous Crop Insights addressed basic agronomic practices that could help increase soybean yields. This article will discuss overcoming pest obstacles to achieving top soybean yields and profits.
Severe SCN damage in drought-stressed field.
SCN has long been the chief nemesis of soybean production in the US. This tiny worm-like parasite has now spread to practically all important soybean production areas of the US, and is reaching economic levels in more and more fields. SCN may decrease yields substantially without inducing obvious symptoms. In fact, studies have shown that in SCN-infested fields, yields can be reduced by over 30 percent without visible above-ground symptoms. Consequently, many fields are infested without the knowledge of the grower. Sampling fields with no symptoms is the only way to detect SCN before it becomes an economic problem.
When SCN is determined to exist at economic levels in a field, growers should implement a combination of management strategies for effective control. This involves continued soil testing to monitor SCN numbers or races, crop rotation, and use of appropriate resistant soybean varieties. Effective nematicides have not been an option in the past, but new products are being tested and may offer another management choice in the future.
If a single genetic source of SCN resistance is used repeatedly, race shifts can occur in a field. For this reason, nematologists recommended rotating sources of resistance, in addition to crop rotation and other management practices. Pioneer offers varieties with the Peking source of resistance, which can be rotated with the common PI 88788 source used in over 90% of soybean varieties currently available in the US and Canada.
In addition to directly managing SCN, any practice which promotes good soybean health and growth will also help minimize yield losses from SCN. Avoiding low soil fertility, compaction, drought stress and other disease and insect pressures will enable soybean plants to better withstand the effects of SCN.
Using the latest breeding tools including Accelerated Yield Technology (AYT) and marker-assisted selection (MAS) allows Pioneer researchers to develop top-yielding varieties while incorporating genes for SCN resistance. These tools greatly improve the efficiency of selection and increase the rate of new product development.
Soybean diseases are one of the most significant obstacles to achieving maximum soybean yields. Even worse, several diseases like sudden death syndrome and white mold appear to be spreading in major soybean states. Variety selection, crop rotation, seed treatments and foliar fungicides are the best tools available to counter most disease threats.
Like soybean cyst nematode, sudden death syndrome (SDS) has spread northward from the southern US, with most Midwest states now affected. Symptoms of SDS usually do not appear until mid-summer or later in the Midwest, but infection occurs in the spring. Soil temperatures below 60° F. are ideal for SDS infection. Like many other soilborne root rots, SDS develops under cool, wet soil conditions and often appears first in low, poorly drained or compacted areas of the field.
Management options for SDS include scouting fields for SDS infection, selecting tolerant soybean varieties, avoiding early planting, improving field drainage, reducing compaction, evaluating tillage systems and reducing other stresses on the crop. Pioneer rates its varieties for tolerance to this damaging disease, and offers 15 varieties with a 7 or 8 rating (on a scale of 1 to 9, 9 = best).
In addition to SDS, soybeans face a number of other serious disease risks, including Phytophthora root rot (PRR), brown stem rot (BSR), white mold and frogeye leaf spot. Geographic location, seasonal growing conditions and soil type determine the presence and severity of these and other soybean diseases. When conditions are favorable for disease development, impact on crop yield can be significant, so these diseases must be successfully managed to maximize soybean yields.
Variety selection is often the best defense against soybean diseases. But for variety selection to be successful, growers must be aware of the disease risks on their fields, the potential severity of the disease, and the degree of resistance or tolerance in available products. In its product descriptions, Pioneer lists the specific genes for Phytophthora resistance incorporated into Pioneer® brand soybean varieties. Product literature also shows variety ratings for Phytophthora field tolerance and resistance or tolerance to brown stem rot, white mold and frogeye leaf spot. Your local Pioneer sales professional can help you select varieties with appropriate disease resistance ratings and other important traits for each field.
Seed treatments are another means of combating seedling diseases. Because of earlier planting and higher levels of crop residue on fields, soils are generally colder and wetter at planting, and seed-ling diseases have increased as a result. Consequently, more growers are seeing an advantage to fungicide seed treatments. Adding an insecticide to the treatment helps prevent insect feeding that provides an entry port for disease infection. Pioneer Agronomy Sciences researchers routinely test seed treatments in multiple locations each year.
In 36 sites-years of Pioneer testing over four growing seasons, fungicide seed treatments (ApronMaxx® and Trilex® AL) delivered a 0.6 bu/acre yield increase (Figure 1). But when a fungicide-insecticide combination was used (CruiserMaxx® and Trilex AL + Gaucho®), the yield advantage jumped to 2.0 bu/acre. This represented a significant positive return on the seed treatment investment.
Foliar fungicide applications to both corn and soybeans have become more common in recent years. Pioneer agronomy researchers have tested foliar fungicides with and without an insecticide included in the tank. Results over five years of testing demonstrated that:
A decade ago, soybean producers worried little about insect pressure to their crop. Soybean aphids were unknown at that time, and populations of bean leaf beetles and other leaf defoliators usually remained below economic thresholds for treatment. In recent years, however, the soybean aphid has emerged as the primary insect pest of soybean, and bean leaf beetle numbers have increased dramatically. In fact, some growers treated for both of these pests in recent years.
Soybean Aphid The soybean aphid has quickly become the major insect pest of soybeans in North America. From its first detections in areas near Lake Michigan in 2000, it has spread to virtually all soybean growing areas of the US and Canada. Because yield losses have often been severe in untreated fields, growers are encouraged to actively manage for this damaging soybean pest. Outbreaks of soybean aphid have generally occurred in an every-other-year cycle, likely due to the dynamics of aphid and predator population levels.
No varietal resistance to soybean aphid is yet available in modern commercial varieties. Current management is by vigilant scouting and treating with an insecticide when required. Treatment decisions are difficult because of the rapid nature of aphid reproduction, and the interaction of aphid populations with natural enemies and weather conditions. However, researchers now have a better idea of the infestation levels that justify an insecticide treatment, and scouting procedures have been simplified to make this process more efficient.
As research on soybean aphids continues, new developments are expected to help reduce losses from this pest. For example, Pioneer and Kansas State University have developed a technique for screening soybean lines for their ability to naturally reduce the rate of growth, survival and reproduction of soybean aphids that feed on soybean plants. This type of resistance is called "antibiosis". Pioneer has used this break-through technique to characterize and rate all current Pioneer® brand soybean varieties for this trait.
Aphid antibiosis ratings should be used by growers to help in determining field scouting priorities and insecticide application decisions. For example, when aphid scouting is recommended in an area, fields planted to a variety with a "Below Average" rating should be scouted first and with greater frequency than fields planted to varieties with "Average," "Above Average" or "Exceptional" scores.
Aphid antibiosis screening techniques also help Pioneer researchers identify superior sources of genetically based aphid resistance in soybean germplasm. Once identified, such sources will be used to incorporate aphid resistance or tolerance into new soybean varieties. Growers are encouraged to stay in contact with their Pioneer sales professional for new research developments and updated information on diagnosing and managing soybean aphids in their area.
Bean Leaf Beetle
When winters are mild, bean leaf beetle (BLB) populations in soybeans may increase dramatically, resulting in increased leaf and pod feeding and virus incidence. Just-emerged soybeans are especially at risk to significant BLB feeding damage when beetle populations are high, especially when planted early and emerging first in an area. Later, during vegetative growth from the V2 stage to flowering, soybeans can tolerate considerable feeding, from 40% to 60% defoliation, without incurring yield loss. However, the second generation of beetles usually peaks during soybean pod-fill stages, resulting in "clipped" or damaged pods. Significant yield loss can occur at this time (usually during August in the midwestern US).
Scouting regularly for BLB and treating if necessary are recommended to address this problem insect. Scouting and treatment recommendations are based on the number of insects found per plant and the developmental stage of the crop. When beetle numbers are high, successful management of this insect is important to maximize soybean yields.
Pioneer encourages soybean growers to test the concept of maximizing soybean yields by conducting their own "personal best" yield challenge on a 5- to 10-acre plot. Below are some tips to help maximize your plot yield.
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