S1010: Dynamic Soybean Pest Management for Evolving Agricultural Technologies and Cropping Systems (S-281)
Statement of Issues and Justification
Soybean pest management is challenged by simultaneous occurrence of biotic (e.g., various insects) and abiotic (e.g., drought) stresses. With new understandings about the physiological basis for yield loss from different stressors, we now have the opportunity to develop better strategies to address combined stressors, which are what most soybean growers experience (Higley 1992). Additionally, the emergence of new soybean production practices, transgenic genotypes, and new insect pests requires research to determine how best to manage insects and other stressors in these systems (Boethel 2002). The potential impact on soybean profitability makes it essential that we begin addressing current and future problems now.
Soybean growers have recently experienced increases in certain insect pest problems and the introduction of a new and potentially significant problem over the past few years. The first situation is the increase in population densities of the bean leaf beetle, Cerotoma trifurcata, and a corresponding rise in the incidence of bean pod mottle virus, a pathogen vectored by the beetle (Rice et al. 2000). This relationship between bean leaf beetle and bean pod mottle virus, previously more common in southern states, is a relative new occurrence in the central and northern United States. The second problem is the recent introduction of the soybean aphid, Aphis glycines (Marking 2001). Soybean growers now are facing widespread use of insecticide over potentially millions of acres of soybean in the upper Midwest and given the native range of this insect, soybeans throughout the United States are at risk of being invaded.
Over the past decade, bean leaf beetle populations have increased to routinely exceed economic thresholds (Rice et al. 2000). Increased soybean acres planted in the Midwest and earlier planting dates are most likely the major factors contributing to the general increase in beetle numbers. The spring colonizing population, which has in the past been a relatively minor concern, is regularly entering fields during seedling emergence and causing great concern to soybean growers. Concurrent with the population increase has been an increase in diseases transmitted by the beetle (particularly bean pod mottle virus) (unpublished data from numerous states). Bean leaf beetle populations have increased dramatically over the past decade, and perhaps is one reason for the increase in bean pod mottle virus. The occurrence of virus-caused symptoms, most notable green stem syndrome and mottled seeds, has caused growers great concern. This has been especially true for growers of food grade soybeans where seed appearance is of utmost importance.
Most recently, the discovery of the soybean aphid in the Upper Midwest presents a new challenge to United States soybean production (Marking 2001). The soybean aphid is a recent invader of North American soybean fields. The aphids native range is from northern China to Indonesia. In 2000, aphids were found in nine Midwestern states (WI, MI, MN, IL, IN, IA, MS, OH, KY) and by 2001 it expanded into the eastern states of PA, NY, VA, WV and south and west into MO, SD, ND and into Canada (Manitoba and Ontario). Soybean aphids can damage plants by reducing photosynthesis (Higley, personal communication) and reducing pod set by as much as 33% (Ostlie, unpublished data). They can also transmit a number of plant viruses and indirectly affect yield by promoting growth of sooty mold on leaf surfaces. Yield reductions in excess of 16 bu/A have been measured with an average loss in grower strip trials of over 6.2 bu/A (13.9%) in Minnesota in 2001 (Ostlie, unpublished data). In the 2000 field season, the highest reported yield reduction was 13% in one Wisconsin replicated experiment (D. Hogg, unpublished data). Given that the aphid has been in the U.S. for a few years, it probably is overwintering successfully on its primary host, buckthorn. However, it is not known which species of buckthorn or other plants could be serving as a primary host, or the potential range of its overwintering capabilities. We currently do not know the present or future extent of the infestation or whether natural enemies are capable of controlling the soybean aphid.
An additional concern with the soybean aphid, similar to the bean leaf beetle relates to aphid transmission of soybean mosaic virus (Boethel 2002). Aphids that do not colonize soybeans have in the past, transmitted this virus. Transmission of this non-persistent virus is from aphids passing through and probing soybeans in search of a suitable host. Symptoms of soybean mosaic virus are similar to those associated with bean pod mottle virus. Plants can also be infected simultaneously with both viruses that result in severely stunted plants. Soybean diseases caused by viruses are reaching near epiphytotic proportions in many parts of the United States. The two viruses of most concern are bean pod mottle, transmitted by the bean leaf beetle, and soybean mosaic, vectored by aphids. Symptoms are similar, and thus, correct identification is crucial. With the recent discovery of the soybean aphid, which is the first aphid able to colonize soybeans in North America, and one that can transmit soybean mosaic virus, the incidence and impact of this virus may increase substantially. Research is critically needed to understand how to manage soybean aphid to reduce spread of soybean mosaic virus, if this disease becomes more widespread due to the presence of the soybean aphid.
The proposed research on pest sampling and injury assessment by precision agriculture technologies is at the leading edge of IPM research. In the dynamic agricultural environment, diminishing resources (in terms of time and effort) must be directed at significant problems that arise quickly and do not respect property boundaries, county lines, and state or federal districts. Landscape ecology focuses on entire agroecosystems and has won favor in the scientific community because many of the large-scale problems cannot adequately be addressed in small plot experiments or even entire fields. Much scientific effort has focused on small scale and limited factor analyses of ecological communities generally associated with agroecosystems. However, this bottom-up approach has been much maligned in the ecological literature because of its limited scope, and because many of these small-scale factors may become insignificant when viewed at landscape scales. Recently, more support has been given to large-scale, landscape analysis of entire watersheds, ecological communities, and agroecosystems. In agriculture, we have seen tangible results from the landscape perspective including: area-wide management of such pests as boll weevil, Hessian fly, screwworm, and gypsy moth. Significant problems face producers and scouts in soybean in the future, and at least some of these problems could be addressed using remote sensing technologies. For instance, nutrient deficiencies, drought stress, insect damage, pathogen infestations, and delayed maturity are all significant problems over broad geographic areas. The solutions to these problems require an area-wide view. Under the auspices of previous soybean entomological regional projects, viz., S-255 and S-281, it has been demonstrated that Leaf Area Index (LAI), a measurement of the amount of leaf area per unit area, could be used as an indicator of problem or great-risk soybean fields (Hunt et al. 1999). Yield losses are likely to ensue when LAI values drop below critical levels because of poor stand, drought stress, soil problems, nutrient deficiencies, insect damage, or pathogens. It also has been demonstrated that infrared photography from a fixed-wing aircraft can detect variations in LAI within a field. The aim of this project is to conduct research on remote sensing of soybean fields to determine risks of yield loss, and in this manner, direct management strategies to those areas where yield losses are likely. This research will incorporate new technology including satellite imagery, digital orthographic images or quadrangles (DOQs), geographic information system (GIS) software, and global position systems (GPS) in current management practices and scouting techniques. Distribution of the information via the Internet also will be a component of this effort. There are no technical restraints to conducting the research although the GIS, GPS research proposed will require greater dependence on equipment.
In summary, the proposed research addresses new and evolving pest problems that demand attention by researchers in all soybean-growing regions. The potential impact of these concerns warrants that efforts begin now. Soybean producers, consumers, and other stakeholders will be the beneficiaries of the research. This group of scientists has collaborated in three multi-state projects, and some of the participants are second generation with their major professors being founding members of S-74. The group is comprised of scientists in virtually every soybean producing state. This is particularly important with the recent invasion of the soybean aphid in the Upper Midwest and Northeast United States. There is already a track record of productivity documented by numerous publications, edited books, southern region series bulletins, and stakeholder focused literature. Perhaps the most noteworthy publication is the Handbook of Soybean Insects (Higley and Boethel 1994) published by the Entomology Society of America, the first of a nationally known series. The addition of new states, regions, and researchers into this group truly gives this project a national scope. Joining all soybean workers will allow those new to the project to share in the long-term expertise that currently exists in S-281, along with bringing in new perspectives from areas outside the typical soybean entomology arena.
The research proposed for the replacement for S-281 addresses the following SAAESD priority areas; Goal 1-A,B,&C; Goal 2-A; Goal 4-F.
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