J. Ingerson-Mahar, D. L. Lee and M. F. Huffaker
Rutgers Cooperative Extension, Salem County
Woodstown, NJ, USA
M. G. Hughes
Rutgers Cooperative Extension
Grant F. Walton Center for Remote Sensing and Spatial Analysis
New Brunswick, NJ, USA
During the past six years, corn and potato crops in southern New Jersey have experienced frequent crop damage caused by wireworms. Bait traps and field observations show that damage is caused most often by Melanotus communis (Gyllenhal). To characterize the temporal and spatial distribution of these wireworms, two corn fields known to be infested were mapped using a real-time Trimble AgGPS™ Model 122 differential GPS unit. Site-specific sampling points were established in each field. Bait traps were placed at each sampling point in the fall of 1998 after the corn silage crops were harvested. Wireworm counts, soil temperature, soil compaction, and elevation readings were obtained at these sites. Too few wireworms were collected to draw any statistically significant relationships among soil temperature, soil compaction, and elevation. GPS/GIS technology is useful in tracking both the spatial and temporal distributions of wireworms and will play a significant role in addressing future wireworm problems for farmers.
Over the last six years a general increase in wireworm damage in southern New Jersey field corn has been observed. Potatoes and, to a lesser extent, wheat also suffer from wireworm feeding damage. Field observations confirm that Melanotus communis (Gyllenhal) is the most common and damaging species for corn and potatoes, while Limonius dubitans LeConte is common in fields where only wheat is grown. Collection of these species is normally made through bait trapping prior to planting the crop. Bait traps provide reasonable estimates of wireworm populations (PSU, 1999), although it is not clear what the appropriate number of traps should be, and how they should be placed for each crop to reliably represent the population of wireworms in the field. Due to the warm spring weather conditions in this region, and the eagerness of some producers to plant as early as possible, spring bait trapping is disruptive to the farm operation. For this reason, baiting fields in late summer (September, October) after crop removal is preferable. This paper is part of a larger study to determine the effect of season on wireworm activity within the soil profile. The objectives for this project were to 1) map wireworm distributions within fields using GPS/GIS technology, 2) verify the species of wireworm present in the fields, 3) determine if specific soil parameters are associated with wireworm distribution, and 4) set up a protocol for gathering data on a temporal basis.
A total of 13 fields ranging from 1.2 to 40.5 ha (3 to 100 acres) in southern New Jersey were sampled for wireworm populations. All fields were on dairy farms, received varying amounts of manure each year, and were in continuous corn for several years. Five bait traps were buried in each of the sample fields. The bait traps consisted of 60cc of grain (corn and wheat seed in a 1:1 ratio) contained in a cheesecloth bag. Each bait trap was buried 5 cm (2 in.) deep and covered with soil. Baits were removed after the seed had sprouted (approximately 12 days), and examined for wireworms. The wireworms were then collected and identified. Two fields, a 1.2 ha (3 acre) field (D1) and a 19.4 ha (48 acre) field (H1), with above threshold populations (more than one wireworm per bait trap) were selected for a more detailed site-specific analysis. Positional information was mapped using a Trimble AgGPS Model 122 differential GPS unit. Output from the receiver was captured in a Fujitsu pen-top computer running an integrated GPS/GIS site-specific agricultural software package by Red Hen Systems, Inc. (purchased through the Farmers Software Association, Fort Collins, Colorado). Site-specific sampling points were generated using a pseudo-random gridding algorithm. This resulted in 11 sampling points for field D1 and 46 points for field H1.
Bait traps were set at each sample point in the fall of 1998 after corn silage was removed from the fields. Wheat cover crops were planted at the time the bait traps were placed. The traps for field D1 were set on October 7 and recovered on October 19, and the traps for field H1 were set November 2 and recovered November 24. In addition to the wireworm counts at each point, elevation readings, soil temperature at a 5 cm (2 in.) depth, and soil compaction at 200 psi and 300 psi (Dickey-John Soil Compaction Meter) were obtained. Spatial maps of the data were generated in ArcView GIS (ESRI, Redlands, CA) using an inverse distance interpolation routine.
A total of 12 wireworms were captured from field D1. Two different species were identified, eight specimens of M. communis and four specimens of Aeolus mellillus Say. Temperatures ranged between 18.9 and 21.1° C (66 and 70° F). The least compacted soils (61 to 69 cm (24 to 27 in.) at 300 psi) were found in the southern end of the field at the lowest elevations. The wireworms that were found appeared to be distributed throughout the field, with the highest concentration found in the eastern part of the field (Fig. 1). Nine wireworms were found in field H1, all of which were identified as M. communis. Temperatures in this field ranged from 9.4 to 12.2° C (49 to 54° F) reflecting the cooler temperatures found in southern New Jersey during late November. The highest temperatures tended to be associated with the highest compacted soils occurring in the higher elevations of the field (Fig. 2). The wireworms found in this field, like the smaller field appeared to be well distributed throughout. No statistically significant relationships between wireworm counts, soil compaction, temperature and elevation were found.
In 1997 and 1998, fields D1 and H1 exhibited threshold populations of wireworms (one or more wireworms per bait trap). An insecticide seed treatment at planting was made in both fields based on this information. Despite the treatment, wireworms continued to be above threshold in both fields. Too few worms were counted in this study to determine any statistically significant relationships among the variables collected. It was previously thought that some species of wireworm prefer damp soil conditions to dry ones (MSU, 1980), and most of the crop damage (based on stand count) did occur in wet or low areas of the fields. In these two fields however, M. communis were collected from low, high, and sloping contours under a range of conditions. This may indicate multiple sources of crop damage. The time of year and cool soil temperatures may also contribute to the low incidence of wireworms. These fields will be sampled again in fall of 1999 at the same sampling points.
This study demonstrates 1) that GPS/GIS technology is promising in tracking both the spatial and temporal distributions of wireworms, and 2) GIS technology is useful for determining associations among a variety of spatially correlated variables. Although this study did not determine with certainty what influences wireworm distribution in the two corn fields studied, a protocol was developed for designing a site-specific study. Through the use of GPS-technology, these fields are being revisited this fall (1999) for further data collection. The affect of different patterns of temperature and precipitation from one year to the next on wireworm distribution will also be examined. Through the use of GPS technology, accurate navigation to the same sampling points will allow us to build both a spatial and temporal map of wireworm distribution. In this way, using site-specific agriculture practices, actions taken by the farmers to minimize the effect of wireworms on their fields can be followed.
MSU, Field Crops Scouting Manual, Department of Resource, Development, Entomology, and Forestry, Michigan State University, 1980.
PSU, The Agronomy Guide 1999-2000, eds. N. Serotkin, and S. Tibbetts, Penn State College of Agricultural Sciences, Penn State University, 1999.