Spatial pattern of infestation risk and management of the invasive brown marmorated stink bug in soybeans
Since its introduction into the United States near Allentown, PA during late 1990s, the brown marmorated stink bug (BMSB) has steadily expanded in population number and distributional range (Hoebeke & Carter, 2003). This invasive stink bug, native to Asia (distributions in China, Japan and Korea), is now found in 40 states within conterminous U. S and Hawaii. While at present they are just a nuisance in many states, the recent explosion in BMSB populations has led to significant economic impacts as agricultural pests. BMSB caused unprecedented crop damage and economic losses particularly in the Northeast U. S. since 2009-2010 across a broad range of cropping systems (fruit, grain, vegetable, field and tree) in the Mid-Atlantic region.
The research/extension community has responded swiftly to the BMSB outbreak and over the past 3 years efforts to understand BMSB invasion and develop management strategies have increased with multi-institutional and multi-investigator collaborations and funding availability also has increased. However, these efforts primarily focus on specialty crops (e.g. $5.7 M USDA NIFA Specialty Crop Research Initiative Grant), and research and extension efforts in field crops, which are not within the purview of such grant initiatives, remains sparse. Particularly, despite soybean constituting high proportion of overall crop area (23% in the US and 8 % or 1645000 acres in Northeastern region; NASS, 2012) and soybean being a preferred host for BMSB (Hoebeke & Carter, 2003), studies concentrating on developing strategies for BMSB control in soybean are few.
In this context, knowledge on the spatial distribution of BMSB abundance in soybean and the factors that influence this invasive stink bug, directly applies to developing integrated pest management (IPM) strategies. The ability of farmers to effectively control BMSB requires knowledge of its spatial distribution within fields and across large landscapes and of how prevailing environmental, habitat factors and regional land use may inhibit or support outbreaks. As part of both site–specific / precision farming and area-wide IPM strategies, measurement of the spatial variability and pattern of BMSB abundances within a field or across a larger landscape is required. This would allow us to develop BMSB management strategies that can be incorporated into existing IPM practices.
The specific objectives of this research project are:
1. To assess the influence of adjacent habitats on spatio-temporal differences in densities of BMSB in soybean field edges.
2. To assess the influence of field level environmental and crop characteristics on the spatio-temporal differences in densities of BMSB within adjacent corn-soybean fields;
3. To assess the influence of land use at multiple scales and environmental factors, on the landscape scale differences in relative abundances of BMSB in soybean fields.
4. To provide a table of infestation risk factors and in-field distribution patterns associated with specific farmscapes surrounding soybean fields and identify soybean production areas with higher vulnerability to outbreak of BMSB.
Objective 1. Field work and analysis for understanding the influence of adjacent habitat on BMSB abundances at the field edge has been completed.
Thirteen soybean fields adjacent to woods, buildings, corn and open areas were chosen at three UMD farm facilities in Keedysville, Clarksville and Beltsville. These fields were each repeatedly sampled (6 times) from Aug 15 to Sept 23 2013, during the pod development stages of the crop which is associated with high BMSB abundances. Counts were made at 8 different distance intervals – from the field edge 0 to 50 feet into the field.
Results are concurrent with previous year’s finding that fields adjacent to woods have higher abundances of stink bugs, followed by building and corn, while abundances were generally low in fields adjacent to open areas. However, there was an overall difference in the number of observed stink bugs across the three different sites with highest abundances found in Keedysville and lowest in Beltsville. This indicates landscape influences on abundances acting at spatial scales larger than the field edge. Currently a mansucript is near completion for submission to peer reviewed journal for publication.
Objective 2. Field work for understanding spatio-temporal differences in densities of BMSB within adjacent corn-soybean fields has been completed and analysis is currently underway. Three soybean fields (2 in Keedysville and 1 in Beltsville) of approximately 1.2 acres each were chosen for sampling. From July 20th to Sept 20th 2013, BMSB abundances were enumerated 10 times, at 36 equally spaced locations throughout each field. This study aimed at understanding pattern of BMSB distribution throughout the field when fields had both corn and woods as one of the adjacent sides. Data showed that in the low density field, adjacent corn is not a major source of BMSB in soybean. But when abundances are really high in corn, the adjacent soybean edges become infested heavily. However, in the same field, densities are still lower than levels of stink bugs on the edge bordering woods. Abundances were very low in the field interior, with only occasional detections 50 feet from woods or corn edge. Detailed maps based on interpolated values, over the different pod filling stages are being prepared.
Objective 3. Influence of landscape, environmental and topographic variables at large landscape scales, on BMSB abundances.
BSMB abundances in soybean fields across a large landscape were recorded through field surveys during growing season of 2013. The study was conducted within soybean fields in a 3000 X 3000 mile study area in Washington, Fredrick, Montgomery, and Carroll Counties in Maryland; Jefferson County in West Virginia and all counties in Delaware. The study area chosen represents the invasion front of BMSB as they move south from PA, encompassing landscapes with varying proportions of forests, habitations, and crop area (Cropscape 2012). The study area was gridded and 83 soybean fields in MD and 40 fields in DE, each at least 5 km apart, were visited and number of BMSB and native stink bugs were sampled and recorded by taking 25 sweeps with a standard sweep net at 3 different sides of the field edge. The soybean growth stage and edge habitat were identified for all three edges. The spatial coordinates for the fields were recorded using a hand-held global positioning system. Sampling was carried out once during Sept 3 – Sept 15 2013, coinciding with the pod filling stage of soybean (R4 – R6), which is associated with higher abundances of stink bugs.
Preliminaly analysis show that density of houses at 1km, mean minimum temperature in June, % forest cover at 250m and developed area at 5 kmm are all important variables that explain variation in BMSB abundances across large areas (Fig. 1). Currently further detailed analysis are being carried out.
Impacts and Contributions/Outcomes
Based on findings from objective 1 of this study currently in Virginia, we worked with seven growers in four counties to validate the efficacy of field-edge-only insecticide treatments for controlling economic infestation levels of BMSB. Follow-up post treatment scouting showed that this management strategy was successful in all fields in keeping BMSB populations low (less than one BMSB per 15-sweep sample) for at least a month after treatment and until plants were mature enough to be safe from injury.
Results from this study have been presented at both professional symposia and extension meetings.
P. Dilip Venugopal, Galen P. Dively, and Ames Herbert. Environmental and spatial factors influencing patterns in stink bug communities in soybean. Eastern Branch ESA. March 2013.
Hooks, C.R.R., P. Dilip Venugopal and G. Dively. Fifteenth Annual Maryland Commodity Classic. Update on BMSB activity and control in grain crops and soybeans. Centreville MD, July 25, 2013.