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Funded Project |
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Funding Program:
Regional IPM Competitive Grants - Northeastern |
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Project Title:
Sweet Corn IPM in Diversified Cropping Systems |
Project Directors (PDs):
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Lead State: PA Lead Organization: Pennsylvania State University |
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Cooperating State(s):
Maryland |
| Undesignated Funding: $149,905 |
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Start Date: Jul-01-1999 End Date: Jul-31-2001 |
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Site/Commodity: sweet corn, vegetables |
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Summary:
Vegetable production in the northeastern exists on diversified farms (growing >1 crop) with an emphasis on direct retail marketing to nearby urbanizing areas. The challenge is to design and implement IPM programs that affect multiple crops simultaneously. One approach would be to start with the major crop, where IPM on that crop would improve IPM on related crops. Sweet corn meets these criteria. Improved management in this crop could directly influence peppers, snap beans and other highly ranked crops grown on the same farmscape. Currently, insecticides remain an essential component for commercial production on the great majority of vegetable farms in the northeast. Reliance on pesticides, however, is becoming increasingly difficult to sustain due to resistance and regulatory changes, notably the Food Quality Protection Act (FQPA). In vegetables, however, the great majority of registered materials rely on modes of action that may not be sustained during the implementation of FQPA. Biorationals with novel modes-of-action could dramatically change commercial production recommendations, and the most notable of these in sweet corn is transgenics. Concurrently, improved monitoring and educational programs have the potential for simultaneously reducing pesticides in sweet corn and the other high-ranked crops in the same farmscape.
The goal of this project is to advance the IPM information on diversified fresh-market vegetable farms by focusing on sweet corn with pests relevant to multiple crops grown on the same farm. The work will emphasize monitoring programs, and experiment with the opportunity of capitalizing on the diversified cropping structure when implementing transgenic sweet corn. Specific objectives include (1): Improved information access and organization with WEB-based structures for multistate collaboration, and incorporation of phenological predictions into monitoring programs, and; (2) Capitalizing on the in diversified crop structure in the implementation of transgenic host plant resistance. We will conduct adaptive work related to trapping moths, and targeted educational programs at specific audiences, including those producing IPM-labeled produce. Data from trapping sites will be coordinated through Extension using modern methods, including WEB delivery of georeferenced trap count data visualized through a map interface, and phenology models that predict the time of occurrence of major pest life stages. Map images will be maintained on the WEB, and will provide a clickable access to a time-series to see how populations are changing over time. Transgenic sweet corn will be tested for its influence upon pest immigration and pesticide management in neighboring vegetable crops. This project, therefore, will provide the basis for moving IPM forward on diversified fresh-market vegetable farms by focusing on education, monitoring pests related to sweet corn and other highly ranked crops, and the influence of implementation of trangenic sweet corn at the farmscape level. Objectives: The goal of the project is to advance the IPM information on diversified fresh-market vegetable farms by focusing on sweet corn with pests relevant to multiple crops grown on the same farm. The work will emphasize monitoring programs, and experiment with the possibility of capitalizing on the diversified cropping structure when implementing transgenic sweet corn. Specific objectives include: Extension: To improve information access and organization with WEB-based structures for multistate collaboration, and to incorporate phenological predictions into monitoring programs. Research: To assess the neighborhood effect of transgenic sweet corn in diversified crop structures and evaluate its feasibility as a farm-scale management strategy. Problem, Background and Justification Commercial vegetable production in the northeastern U.S. exists mainly on diversified farms with an emphasis on direct retail marketing to an increasingly urbanized community. A mix of high-cash crops are grown including sweet corn, melons, pickling cucumbers, tomatoes, potatoes, leafy greens, beans, peas, crucifers, eggplant, peppers, and many others. These crops constitute a major source of income for growers and collectively contribute significantly to the economy of the Northeast region. Significant gains in the implementation of pest management approaches have been made for some of these vegetable crops; however, pesticides are still the mainstay and growers continue to be plagued by many weed, insect, disease and wildlife pests. Because of the close proximity of vegetable production with urban neighbors, pesticide use and its potential negative effects are major issues in the Northeast. Increased development and adoption of IPM practices on vegetable crops are clearly needed. Of the 8 reports resulting from the Phase I National IPM Implementation Program for the Northeast Region, 2 involved vegetable growers, and this project is designed with respect to these grower-defined needs. Diversification in vegetable production helps ensure economic sustainability in the Northeast. This complexity of farming, however, is problematic for IPM, which evolved from a single crop-based paradigm. A well-designed IPM program for a given crop (e.g., cabbage) becomes logistically difficult to implement on a farm growing cabbage, tomatoes, sweet corn, peppers, beans, peas and lettuce. In Phase I surveys, the need to provide environmentally sensitive IPM tactics that simultaneously impact multiple vegetable crops in the context of whole farm management was clearly identified. Furthermore, increasing concerns over pesticide use, especially around urbanized areas, necessitate the development of sustainable alternative practices (NRC 1989). Most sustainable practices developed to date (e.g. conservation tillage and cover cropping) have focused largely on alternative management within a particular crop field. We need to broaden the scale of management to whole farm and community-level processes that influence pest problems. The challenge, therefore, is to design and implement IPM that affects multiple crops simultaneously. One approach would be to implement practices on the major crop that improve IPM on nearby crops that share the same pests. Sweet corn is a likely candidate for this approach. It is clearly the top ranked crop out of 35 crops grown on diversified farms in New York, New Jersey, Maryland, and Pennsylvania, with 60% of farms reporting commercial sweet corn production (USDA/NASS 1997, Hoffmann et al. 1996). In Pennsylvania, 72.4% of the farms grow sweet corn. Surveys show that the average diversified fresh-market grower in Pennsylvania derives 22% of the farm income from sweet corn, where 69% of the fresh-market crop is sold retail. In Pennsylvania, of a total 101,600 acres in vegetable production with a farm-gate value of $304,000,000, approximately 21,000 acres of fresh-market sweet corn are grown, with a $60,000,000 value, resulting in a #4 ranking among states for fresh-market sweet corn. In Maryland, sweet corn is also ranked 1st in acreage, accounting for 38% of the total acres harvested for fresh market vegetables. Socioeconomic factors also cause sweet corn to dominate in northeast states. Sweet corn is often the 1st significant crop transition in farms that integrate vegetables into dairy or field crop enterprises. Sweet corn can be adopted with less change in equipment, knowledge, and labor than other vegetable crops, and has a high return, with sample budgets showing $2,800 gross and $1,799 net returns, per acre (Orzolek et al. 1995b). Another important feature of sweet corn production that justifies its status as a focal point for a multi-crop IPM program is the amount of insecticides used. Sweet corn receives more insecticides than most vegetable crops, and it is striking to note that the acreage in the U.S. represents only 1% of the total acreage planted to field corn, yet sweet corn receives nearly 60% of all insecticides applied to corn for lepidopteran pests. According to USDA statistics (NASS, 1996), insecticides were applied to 89% of the sweet corn acres planted for fresh market with an average of 9.2 applications per acre. This represents an average of 2.9 lbs of chemical ai per crop season, which is significantly higher than the amount of chemical ai applied to cotton for control of all insect pests. Although these statistics are based on nationwide surveys, including Florida and Georgia production areas where insect pressure is much higher, insecticide use on sweet corn in Pennsylvania and Maryland is still more than most other vegetable crops. Management of the major insect pests of sweet corn would directly influence other crops on a diversified fresh-market farm. All of the surveys repeatedly confirm that the major pests of sweet corn are the European corn borer (ECB), corn earworm (CEW), and fall armyworm (FAW). At least 1 of these is a pest in 6 of the top-ranked 18 crops on the diversified Pennsylvanian farm (sweet corn, tomatoes, peppers, potatoes, snap beans, and peas). In Maryland, the rank order of crops differs - sweet corn, melon crops, potatoes, tomatoes, snap beans, and cucumbers as the top 6; and at least 1 of the species is a major pest of 5 vegetable crops. Of the crops shared by both states and with significant overlap in pest species, both temporally and spatially on diversified farms, include peppers and snap beans. Peppers is the number 4 crop in Pennsylvania with sample budgets showing $7,700 gross and $3,124 net returns, per acre (Orzolek et al. 1995a). Peppers are not in the top 6 crops in Maryland but are a major crop in the Delmarva Peninsula (including Delaware and Eastern Shore Virginia). Both snap beans and peppers are high-value crops that share ECB and CEW as major pests. Overlap in pest species also occur for potatoes on these diversified farms; however, this crop serves as an early season ECB host prior to significant recruitment in sweet corn. Thus, ECB management in sweet corn would have little in-season impact on this insect's population dynamics in potatoes. Realistic pest management must also recognize important variation within the crop systems. Peppers vary with respect to color, taste, and growing requirements. The trend is toward longer-season varieties with increased sugar content that turn red or orange, which bring higher prices and require pest control over longer time frames. Snap beans are grown both for fresh market and processing. Multiple plantings and even double crops in Maryland are typical for this short-lived crop; thus decision support systems and pest management practices must be dynamic to account for changes over the entire cropping season. Also, monitoring and decision rules differ drastically for fresh market versus processing snap beans. Sweet corn production systems differ in many ways that influence IPM practices. For the processing market, "su" varieties are used. This crop usually consists of larger plants structured in larger blocks, which typically withstand higher rates of stalk tunneling or damage to the ear than crops grown for fresh market. Of the fresh-market varieties, the "sh2" types are typically grown for wholesale. They withstand transport and are grown in more uniform stands. Higher sugar contents are typically achieved in the "se" types. These do not ship as well, and are grown for direct retail. Most growers in Pennsylvania and Maryland use these se varieties in multiple plantings to ensure a continuous supply for the retail fresh-market. The earliest plantings, which are transplanted into plastic mulch in Pennsylvania, are in a group by themselves with respect to pest management, due to a much higher risk to early-season pests and their higher value. At the other end of the season, another high value corn that is increasing acreage quickly is ornamental corn grown for the fall market. Two addition sweet corn systems have recently emerged and have received much attention among IPM workers. They include sweet corn grown with the intent of obtaining an "IPM Label", and transgenic Bt sweet corn. This project will advance IPM in these different marketing systems in the context of the diversified fresh-market farm. STATUS AND WORK TO DATE Insecticide status. Insecticides remain an essential component for commercial production on the great majority of vegetable farms in the northeast. In surveys, only 1-2% of vegetable growers classified themselves as organic. Reliance on pesticides, however, is difficult to sustain due to resistance and regulatory changes. Over 500 arthropods exhibit resistance (Georghiou 1986). Of the arthropod pests in vegetables (from grower lists in Hoffman et al. 1996, Fleischer 1991, unpubl.), resistance is documented in at least Colorado potato beetle, diamondback moth, melon aphid, several whitefly species, mites, sciarid flies, and corn earworm. Secondly, the Food Quality Protection Act changes federal laws that govern pesticide registrations. This will make maintenance of registrations with common modes-of-action that also affect mammalian physiology more difficult. In vegetables, the great majority of registered materials that are currently recommended (Orzolek et al. 1997) fall into the organophosphate and carbamate classes, notably acetylcholine esterase inhibitors at the synapse or interference of sodium channels along the axon, both of which affect mammalian physiology. Sales data suggest that ~ 80% of all insecticides use these modes-of-action (Leicht 1996), and recommended uses (Orzolek et al. 1997) and personal observation suggest higher percentages. Sweet corn growers rely heavily on sprays during tasseling and silking. The risk of infestation at harvest depends on when eggs are laid relative to crop growth stage. Insecticides are recommended from the onset of silking to 5 days prior to harvest in the northeast (Dively 1996), or from the start of "row tassel" (anthesis, early silking) to 10 (fresh market) and 18 days (processing) prior to harvest in the midwest (Flood et al. 1995). Of the pesticides listed for concern with FQPA, growers heavily use methomyl, thiodicarb, and carbaryl. They also use carbofuran or dyfonate during vegetative stages for first generation ECB, and carbaryl for flea beetle (due to its concern as a vector of a bacterial disease). Increasingly, pyrethroids, especially lambda-cyhalothrin, are being used. Data for New York, New Jersey and Pennsylvania (Hoffman et al. 1996) show that sweet corn is the top ranked crop for "IPM/Conventional" growers, but drops to the 20th ranked crop for organic growers. This minor status of sweet corn on organic farms is due in large part to problems with insect management, as opposed to weed, disease or nutrient management in sweet corn. As in field corn, there is also insect pest issues related to stand establishment, but much of this is dealt with using crop rotation. Other pests (sap beetles, etc.) are important, but lepidopteran larvae are consistently ranked higher by growers. Pepper and snap bean growers rely heavily on insecticides in the mid-Atlantic states, primarily for ECB. Also, aphids on peppers and potato leafhoppers on snap beans are secondary pest targets for chemical control. Sprays are typically applied in peppers when fruit are 1/2 inch or larger and ECB are being caught in traps. For snap beans, insecticide treatments begin when catches average > 25 per 5 days. The 1st treatment is during bud to early bloom, and a 2nd application is during late bloom-early pin. As moth activity increases, tighter schedules may be warranted if tolerance for contamination is low. Acephate (Orthene) is the most common insecticide in both crops. The systemic nature of acephate helps ensure efficacy against ECB, preventing the larvae from moving into fruit or pods. However, maintenance of a systemic organophosphate in a food crop in a time of FQPA is a concern. Also, spray timing becomes critical during harvest, as growers of multiple plantings balance the days-to-harvest interval (dhi) against market requests with very short advance notice. Acephate has a 7 dhi, so growers shift to methomyl (a carbamate also targeted by FQPA) or pyrethroids that are labeled and have a shorter dhi. When market requests exceed what can be delivered from a planting block that meets the harvest restriction requirements since the last spray, growers are faced with the decision to either decline market offers or pick from a block that may be close to meeting the dhi. Dively (1986a, 1986b) describe the biology and economic impact of ECB on peppers and snap beans. In both crops, ECB oviposit on leaves and early instar feeding on foliage takes place for 5 to 7 days. The larvae then bore into pods or young peppers under the cap, and feed on the interior tissues. Some stem tunneling occurs but larvae prefer to attack the pods or fruit. Damage is hard to detect and results in premature ripening of peppers, reduced yields, and secondary invasion of fruit rots. Contamination of both fresh and processing raw product is worse than effects on yield, especially in snap beans. Many infested pods and peppers are not detected and culled, moved into the food chain, and damage the business reputation of the supplier. Biorationals with novel modes-of-action could dramatically change recommendations in vegetables. Relevant examples include microbial metabolites (avermectins, emmamectin benzoate, sprayable Bts, and spinosads), nitroguanidines (imidacloprid), botanicals (azadirachtin), and ecdysone agonists (tebufenozide). These have or will have a significant influence on pesticide use patterns in tomatoes, potatoes, eggplant, and all cruciferous crops. In sweet corn, however, there are currently no efficacious biorationals for control of the three major lepidoteran larvae except transgenic Bt hydrids. This is due in part to the habit of the larvae boring quickly into the crop, preventing significant ingestion of foliar materials (currently available biorational systemics, such as imidacloprid, do not have lepidopteran activity). Pest complex and monitoring. Of the 3 major lepidopteran pests, immigration of ECB occurs throughout the cropping season in the northeast, whereas immigration of CEW and FAW is primarily later in the season. ECB overwinters well as late-instar larvae within corn stubble. During the 1st generation, emerging adults invade sweet corn and management decisions are based on in-field estimates of feeding damage, except in the transplanted sweet corn which is already in reproductive stages during 1st generation ECB. However, early-season ECB do not always create problems to the ear in most plantings, and can be subject to high rates of natural mortality (Labatte et al. 1997, Coll and Bottrel 1992). Subsequent generations that immigrate or re-infest sweet corn as it begins to form reproductive structures require the most insecticide sprays. Oviposition during these growth stages is much more correlated to direct damage to the harvested ear. Thus, detecting the time and intensity of invasion relative to the sweet corn growth stage is the major monitoring requirement. It is also the 2nd and later generations of ECB that are of most concern in snap beans and peppers. CEW and FAW do not overwinter well in the northeast, although there is some overwintering of CEW on the Delmarva Peninsula and southern New Jersey. When they invade, however, CEW can quickly cause direct ear feeding. FAW is more known for feeding on both vegetative and reproductive structures, but personal observations have shown significant direct ear feeding if the flights correspond to reproductive growth stages. Thus, detecting these invasions is the major monitoring requirement. In all 3 cases, timing and intensity of invasion is correlated to time of oviposition and intensity of damage, and this information can be used to time application of insecticides. This approach to sweet corn IPM and pest life cycles are described in excellent educational materials in Flood et al. (1995) and chapters 12, 13, 14, and 16 of Adams and Clark (1996). Detection systems have been based on a combination of traps baited with sex pheromones for the CEW and FAW, and blacklight traps for the ECB. Decision-making guides based on the timing and intensity of trap captures of all three species are detailed in Dively (1996), and decision-guides for single species are provided in Flood et al. (1995). All of these, however, assume that ECB data are available from blacklight traps. Detection systems for the ECB using traps baited with sex pheromones have been developed since the mid-1980s. The ECB consist of at least two races (and hybrids) that respond to different mixtures of 2 isomers of the sex pheromone (Glover et al. 1991). Sex pheromone systems of ECB depend on the ratio of the component compounds Z-11-tetradecenyl acetate ("Z") to E-11-tetradecenyl acetate ("E"). The 3 identified systems are 3:97 (3% E:97% Z), 99:1 (99% E:1% Z), and a 65:35 (E:Z) F1 hybrid, referred to as the Z, E, and hybrid races, respectively. Pheromone trapping for ECB management was demonstrated in 1985 (Ferro and Fletcher-Howell 1985) and deployed within a New York IPM program by 1989 . However, Bartels et al. (1997) reported difficulties with commercial sources of lures in Minnesota during 1992-1994, and called for a renewed emphasis on quality control in production of lures. Due to the very specific ratios that distinguish races and that are attractive to males, lures may not have worked because of quality control problems related to ratios in the lures, or because of polymerization of the aldehydes preventing volatilization of the correct pheromone or pheromone blend. In Maryland and some other states of the northeast, the infrastructure for blacklight trap data collection exists with cooperation from state government. In other parts of the northeast, including Pennsylvania, no such governmental structure exists. In this absence, Pennsylvania initiated an informal infrastructure in 1992, with Extension agents running blacklight traps, and the data collated and disseminated by one of the authors (SJF). In adaptive tests during this time, we also observed very low captures with commercial lures during times of high capture in the blacklight traps in 1992 and 1995 (Fleischer, unpubl. data). However, in 1995, we dosed rubber septa with 10 ul quantities of chemicals purchased from Sigma. Our lab-made lure preformed as well or better than blacklight traps at 5 sites in 5 counties , and in 1996 we had success with commercial lures from Hercon . Although not studied thoroughly, trap placement influenced capture, and good field knowledge about ECB could be used to improve placement. Extension agents in 15 counties in Pennsylvania strongly argued that the benefits of a pheromone-trapping program for ECB strongly outweighed the concerns. Currently, Pennsylvania uses a pheromone program, with traps set for both races, and Maryland has an established network of blacklight traps. Extension publications now discuss traps baited with sex pheromones for monitoring ECB activity (Mason et al. 1996). Management can be improved by following up with in-field scouting of immature stages, although this would probably need to occur independently in multiple plantings. In New York, sequential sampling using thresholds of ECB egg masses has been proven effective in processing sweet corn (Shelton 1986). Sequential sampling plans using thresholds of percent infested plants, regardless of species, have also recently been developed for fresh-market sweet corn in New York (Hoffman et al. 1996). The 6 year experience with trapping programs for sweet corn growers in Pennsylvania resulted in an average of 20 to 33% reduction in sprays for the majority of growers (who were relying on 2 sprays/week/planting). Other growers, who relied upon 1 spray/week, had a reduction of ~ 10% and improved timing of sprays. All growers showed an increased understanding of the biology of the pests, and thus are in a better position to utilize new selective alternatives. In both states, we have not yet seriously experimented with using this type of monitoring data for ECB management in peppers or other vegetable crops, however, we are told by pepper and bean growers that they use the information to influence management. Snap bean growers, who now typically time 1 spray at pin set and possibly a 2nd at early pin, will make a firm decision about this second spray, and sometimes add a 3rd, based on ECB trends. Pepper growers are similarly influenced, either with regard to spray frequency or some in-field scouting. In both cases, the pest they are watching is ECB. Clearly, monitoring programs could be simultaneously adopted for beans and peppers, but very low thresholds make it difficult to base decisions on trap capture. What is needed is correct timing or prediction of ECB phenology. Phenology modeling for ECB is well documented and validated (Calvin et al. 1991). The predictive capability is influenced by the biofix used to initiate state variables, and the time span for prediction. A biofix of January 1, assuming the entire population was in the late larval stage, was less predictive than sampling larval stage structure after the 1st generation and using sampled measurements as a biofix (Fleischer and Calvin, unpubl). In the latter case, predictions were of a shorter duration - typically 3 to 5 weeks - but still very useful to determine the time of onset and end of the 2nd generation flight, and subsequent generations, which is when the data would be of most use for most vegetable crops. However, we have not seen much implementation of phenology modeling of ECB in vegetable crops. Although the technology is well established and commercially available, education and delivery to diversified vegetable growers for multiple crops have lagged behind the research or the implementation in field corn. In contrast to the complexity of pheromone trapping for ECB, pheromone trapping to define the time of significant immigration of CEW has been consistent with commercial lures. Pheromone-trapping for FAW with commercial material has also preformed well, except for very large non-target catches in Pennsylvania and Maryland of what is tentatively determined as wheathead armyworm. FAW lures are available as 2- or 3- or 4- component lures, and the 2-component lure is suggested to reduce non-target captures in New York (Knodel et al. 1995). The 4-component lure has been used in Pennsylvania and Maryland. Adaptive tests with the different lures need to occur prior to changing the trapping system throughout the states. Extension education materials exist for pheromone trapping for all 3 lepidopterans in sweet corn (Knodel et al. 1995). Transgenic Bt sweet corn. Genetically modified hybrids resistant to ECB and other lepidopteran pests are already gaining widespread adoption in field corn and may soon fill a niche for biorationals in sweet corn. Transgenic Bt sweet corn is now commercially available as a processing variety ("AttributeTM Insect Protected Sweet Corn", a product of Novartis Seeds). The plant expresses the Cry1A(b) delta-endotoxin protein from Bacillus thuringiensis. The 1st year that transgenic sweet corn could be legally grown on a commercial scale was 1998. In 5 tests in Pennsylvania, AttributeTM had much higher percent clean or saleable ears than its isoline (Appendix 1). At 3 sites the % clean ears was > 96% with no insecticide, compared to 15 to 31% clean ears for the isoline. Lower values came from Erie (87%), due to strong FAW pressure, and Berks County (74%), due to a combination of sap beetles, FAW, and drought stress associated with a shale outcrop. AttributeTM displayed the best control with the ECB and CEW, and less control when very high FAW pressure was present (Appendix 2). The Landisville site was remarkable in ECB pressure, with 332 live larvae per 100 plants in the isoline, and 0 in the AttributeTM. AttributeTM was effective against CEW at all 3 sites with CEW pressure. AttributeTM did have problems with FAW at 2 locations. Although AttributeTM reduced the numbers of live FAW significantly, there remained between 10 (at Fair View) and 18 (at Kutztown) live FAW per 100 plants in the AttributeTM treatment. Similar results of high level of efficacy have been reported from 3 years of testing AttributeTM sweet corn in Maryland. Transgenic su hybrids, combined with planting date management to avoid FAW, will undoubtedly reduce foliar sprays in processing sweet corn. Wholesale fresh-market (sh2) hybrids are expected very soon, and we have reason to believe se hybrids will follow and be available within 2 to 3 years. Use of transgenic sweet corn on diversified fresh market farms raises an interesting "trap-out" opportunity. Because of the close association of sweet corn with other vegetable crops (e.g. snap beans and peppers) that share the same lepidopteran pest complex, the high-dose feature of a Bt hybrid may effectively achieve pest management in both the sweet corn field and nearby host crops. This scenario is more likely in relatively small plantings such as in Pennsylvania and the central-western regions of Maryland, where plantings may well be in strips along contours. If adult moths preferentially immigrate into transgenic sweet corn and no moths of the next generation emigrate out, then the overall suppression may enable farm-level management of ECB. Although ECB has an extremely wide host range in the literature, it has a strong preference for corn over other crops and weeds, including potatoes, when these hosts were grown in close proximity (Calvin, unpubl., Table 1, below). These data suggest an order of magnitude higher larval density in corn than in other crops and weeds. Several documents from research committees and resistant management panels have addressed the "trap-out" capability of transgenic corn. As such, it is sometimes referred to as a "halo-effect", or "edge-effect", that extends into adjacent non-Bt host crops. Recent studies under high ECB pressure have reported that significant reductions in damage of up to 50% can occur in non-Bt corn within 5-10 meters of Bt corn (Andow & Alstad in prep). Damage increases gradually with distance from the Bt corn, but some suppression continues out to 80 meters. Theoretical simulation models (Alstad and Andow 1995; Onstad and Gould 1998b, Onstad and Guse unpublished) also have predicted this phenomenon. Based on these data, a recent position statement from the USDA-CSREES North Central Regional Research Committee (NC 205) recommends that refuge strips of non-Bt corn 6-12 rows wide are effective at delaying resistance, and by positioning these refuges near Bt corn, producers could extend the protection benefits of Bt corn into the refuge, resulting in increased yields. On diversified fresh market farms, this spatial arrangement may already exist because we are working primarily with edges in the landscape. We should recognize this, and consider that implementation of transgenic sweet corn in a diversified farmscape may have unique influences upon pest management. To address resistant management, ECB movement and host preference under realistic field scales has been studied in Pennsylvania (D. Calvin, unpubl). In 1998, ECB pupae reared on red and blue dyed diet were obtained from Dr. Rick Hellmich's USDA/ARS laboratory were released from protected cages. Between 14,412 and 16,412 adults emerged. Assuming a 1:1 sex ratio, ~ 7,206 to 8,206 females were released from a central site. Recapture of colored eggs was examined on 3.4% of the corn plants in 1.46 acre. The recovery rate was 1.40 and 3.17%, and was sufficient to detect movement in the landscape. Host choice was strongly influenced by crop growth stage, which was manipulated by planting date. Egg recruitment studies under field conditions have clearly documented the strong choice for V12 and early reproductive (R1 to R3) corn growth stages (Calvin and Spangler, unpubl.), which is when sweet corn is harvested (see Ritchie et al. 1992 for corn growth stage descriptions). The methods could be adapted to study the influence of transgenic sweet corn in a diversified vegetable farmscape. Table 1. ECB host choice under field conditions in central Pennsylvania Host Name.............Larvae Per Plant........% in Each Host Corn (Zea mays).........................119...79.1 Potato (Solanum tubersum)................11....7.3 Soybeans (Glycine max)....................0....0 Oats (Avena sativa).......................0....0 Common Ragweed (Ambrosia artemisiifolia)..3....2.0 Giant Foxtail (Seraria faberi)............4....2.7 Lambsquarter (Chenopodium album)..........1....0.7 Smartweed (Polygonum pensylvanicum).......1.5..1.0 Barnyard grass (Echinochloa crus-galli)...8.5..5.6 Outcomes and Impacts Summary from 2001 IPM Center report Commercial vegetable production in the Northeast exists mainly on diversified farms that grow more than one crop. The high-cash crops on these farms, such as tomatoes, potatoes, sweet corn, and leafy greens, contribute significantly to the economy of the region. In Pennsylvania alone, for example, vegetable production has a farm value of $300 million, with sweet corn accounting for 22 percent of the farm income. Grown on more than 100,000 acres in the Northeast, sweet corn receives more insecticides than most vegetable crops -- often two to five applications per season per planting. Researchers in Pennsylvania and Maryland found that through IPM, they were able to reduce sprays for European corn borer on sweet corn by up to 33 percent, which may allow them to improve IPM on related crops that share the same pests. They continue to study other innovative IPM strategies that could be beneficial on a whole-farm scale. The project leaders have created a website that links with geographic information systems in a way that can dramatically improve the monitoring of pests that infest sweet corn, potatoes, peppers, and snap beans. The Northeast Region IPM grant led to the creation of a monitoring band that stretches from the Atlantic to Lake Erie, creating a "southern front" for monitoring pest immigrants into the Northeast. This five-state collaborative effort allows growers to understand what's happening on their farms in the context of the region and will potentially give them advance warning of pest pressure. The website is catching on: the number of user sessions almost tripled over the last two seasons, reaching 2,851 in 2000, a significant improvement |
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