[Note to online version: The report for this project includes tables that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact North Central SARE at (402) 472-7081 or email@example.com.]
The European corn borer (ECB), Ostrinia nubilalis is a serious pest of corn in the Corn Belt, causing estimated yield losses in the Midwest from $50 to $120 per hectare of corn (est. $20-$50/acre). With increasing restrictions on insecticides, the call for sustainable agriculture, federal mandates for less surface and ground water remediation and to have 70% of crop land under IPM by the year 2000, necessitates innovative methods to control this pest.
In 1996 and 1997, we conducted on-farm research, with cooperators from the Practical Farmers of Iowa (PFI), in a biointensive approach to managing this insect. In 1997, we also conducted research on an additional farm not affiliated with PFI. An entomogenous fungus Beauveria bassiana, that develops a unique endophytic relationship with the corn plant was employed in this management technique. In 1996, the fungus was applied to corn at the whorl stage, pollen-shedding stage and at post-harvest to manage the first generation, second generation, and overwintering ECB. In 1997 the fungus was applied only at the whorl stage of plant growth. In small field plots B. bassiana has been shown to reduce plant feeding during the growing season and B. bassiana present at harvest kills overwintering larvae, reducing the following year’s population. Once this fungus is placed in the ecosystem it will maintain itself in the soil, crop residue, and the growing corn plant. At this time in our research we do not know how often B. bassiana must be applied to the ecosystem to maintain the ECB below an economic threshold. If this scenario is practiced over a wide area it may be possible to maintain the ECB below an economic threshold without use of synthetic chemical insecticides. This approach may completely transform ECB management. Primary benefits of this proposed research are: (1) reduced producer dependency and exposure to synthetic insecticides, (2) less environmental contamination, and (3) a contribution to long-range goals of reduced environmental and ecological disruption from overuse of insecticides.
On farm research was conducted to evaluate Beauveria bassiana for season-long suppression of the European corn borer (ECB). A commercial preparation of B. bassiana, Myco 9701, Mycotech, Butte, MT, was applied to plants at 0.4 g/plant (ca. 2.2 x 1012 conidia per acre), with a hand-held inoculator. Treatments were applied to corn at whorl-stage (V7), pollen-shed stage corn (R1), to crop residue at post-harvest and corresponding untreated checks. In 1997, the treatments were B. bassiana applied only at whorl stage and an untreated check. Experimentation was conducted on three farms, Practical Farmers of Iowa (PFI) in 1996 and the same PFI Farms and an additional private farm in 1997.
Data were collected on number of cavities made by ECB larvae, tunneling by ECB larvae, number of plants with no apparent feeding by ECB larvae, number of larvae in a plant infected with B. bassiana and grain yield. In both years an application of B. bassiana to V7-stage corn caused reductions in the number of cavities, amount of tunneling and an increase in number of plants without ECB feeding. These statistically significant differences did not always occur at all locations. In 1997, there were also significant differences in reduced number of cavities, tunneling and an increase in non-damaged plants and a statistically significant increase in grain yield on one farm. B. bassiana had no significant affect on overwintering ECB when applied at post-harvest. Even though B. bassiana caused a reduction on insect damage, related increase in grain yield was apparent only in one trial in 1997. Yield, however, is dependent on many things in addition to insect damage. All yields except the latter were from small plot evaluations whereas the latter was taken from 1600 row ft per treatment replication. The large plot most likely reduced inherent variability. B. bassiana is indigenous, an environmentally friendly approach to ECB management and is maintained in the ecosystem.
1. Develop methods to use Beauveria bassiana for on-farm within season suppression of first and second generation European corn borer larvae.
2. Document that the use of B. bassiana in Objective 1 combined with a harvest application of B. bassiana for overwintering European corn borer larvae will provide multi-season suppression.
Investigations were conducted at four locations, i.e., Alert Farm, Hampton, IA; Brunk Farm, Eldora, IA; McLaughlin Farm, Cumming, IA and Bruck Farm, Panama, IA.
In May/June plant residue was sampled for ECB at each farm site in close proximity to the experimental field. The plant residue from 10-1m² samples was dissected. The following data were recorded: ECB larvae killed by B. bassiana, dead larvae (not killed by B. bassiana), and parasitism by Macrocentrus grandii.
Accepted agronomic practices were used to plant hybrid field corn at all cooperators farms. Agronomic practices were dependent on each individual farmer. Only general, not statistical, comparisons were made between locations, i.e., each location was considered a separate experiment.
In 1996, B. bassiana (Mycotech 9701, Mycotech Corporation, 630 Utah Ave., Butte, MT 95701) was formulated on corn grit granules (14-20 mesh) at 1 x 10¹² conidia/lb. This formulation of B. bassiana was applied to corn at .4 g/plant (ca. 2.2 x 10¹² conidia per acre) with hand-held applicators (Davis and Oswald 1979). Applications on the Alert Farm were made when plants were at V7 (early to mid whorl), R1 (pollen shedding) growth stages (Ritchie et al. 1986), and post-harvest. At the Brunk and McLaughlin Farms applications were made at the V7 stage and post-harvest. The experiment was designed as a randomized complete block with six replications. Treatments were application of B. bassiana at V7 stage, R1 stage of plant growth and post-harvest. There was an untreated check in each replication.
Prior to harvest by each participant, the number of plants in 2 rows, each 6.7 m in length, were picked and the stalks were split from the tassel to the base of the plant. Centimeters of tunneling by the ECB, the number of larvae exhibiting a mycosis caused by B. bassiana and yield were recorded. Also, prior to harvest 10 plants per treatment/replication were cut and assayed for the presence of endophytic B. bassiana by the technique developed by Lewis and Bing (1991). The corn plant was surface sterilized with 95% EtOH, split and tissue excised from 3 nodes above and 3 nodes below the primary ear. This tissue was then placed on agar favoring growth of B. bassiana (Doberski and Tribe 1980) and placed in a microbial growth chamber 27°C, 50% RH and total darkness. After a 10 day incubation the presence or absence of B. bassiana was recorded.
After harvest, 2-1m² samples of crop residue were taken in each treatment/replication. These samples were taken by randomly tossing a 1 m² steel frame. All corn stubble and residue were examined for ECB larvae. The number of ECB larvae were recorded. These larvae were categorized as alive, killed (due to harvesting), or infected with B. bassiana. All data were analyzed by ANOVA (SAS Institute, Inc. 1990).
A one-year extension (non-funded) was requested and granted. This extension allowed a second year of field research to confirm/substantiate findings of year one. Cooperators and research methodologies were identical to 1996 with the following exception: (1) Treatments were reduced to two at the PFI cooperators, i.e., an untreated check and an application of Myco 9701 at 0.4 g/plant applied at V6 stage of plant development. Plot length was reduced from 400 to 100 ft. (2) An additional farm site was added, i.e., research was conducted on the Allen Bruck Farm, Panama, IA. This research was conducted to also determine the efficacy of applying Myco 9701 to V6 stage corn to manage the ECB. The experiment was designed as a randomized complete block, 4 replications of 4 rows of corn (0.75 m centers) 400 ft in length, separated by 8 guard rows. There were two treatments, an application of Myco 9701 at 0.4 g/plant at V6 stage of plant development and an untreated check. Applications were made using a hand-held applicator. At plant senescence 25 plants per treatment/replication were split from tassel to base and the number and length of tunnels made by the ECB were measured and the number of mycotic larvae recorded. Data were analyzed using ANOVA and means were separated using Student’s t-test for multiple comparisons (SAS Institute Inc. 1990). All 1600 ft of row from each treatment/replication were harvested with a conventional four row combine. Yield data were then obtained with the use of a conventional field weigh wagon.
In 1996, data on ECB and mortality factors in 1996 are presented in Table 1. The percentage of 1995 overwintering mortality from B. bassiana was similar at all three research sites. This is in the normal range of overwintering mortality of ECB larvae from B. bassiana that has been reported from Central Iowa (Lewis, unpublished data). Parasitism by M. grandii was very low, which is normal for this parasite (Lewis 1982).
Efficacy data of B. bassiana are presented in Table 2. Statistical comparisons are made within locations. Only general statements can be made about data between locations. At all locations the mean number of cavities per plant was significantly lower when the plants had B. bassiana applied at whorl stage. At the Alert Farm, B. bassiana applied at whorl stage of plant development decreased the amount of tunneling by the ECB significantly more than when it was applied at pollen-shedding stage. The percentage of reduction in tunneling at the Alert Farm compared to the untreated check were 55.4 and 23.1 respectively for B. bassiana applied at the whorl and pollen-shedding stage of plant development. At the Brunk Farm, B. bassiana reduced tunneling by 53% and by 46% at the McLaughlin Farm when applied at whorl stage. These percentages of insect control are typical of a microbial insecticide.
At all locations the greatest number of plants with no tunneling by the ECB larvae were in the plots that were treated during the whorl stage with B. bassiana. At the Alert Farm there were no significant differences between the number of undamaged plants in the pollen-shedding treatment and the untreated check. One possible interpretation for the large numbers of undamaged plants in the whorl-stage treatment is that those plants were colonized by B. bassiana which killed any larvae that attempted to feed on the plants (Lewis and Bing 1991).
There were no differences in grain yield between any of the treatments. Even though insect feeding was significantly reduced it did not translate into increased yield. Obviously, many things contribute to yield, not only insect pressure.
Post-harvest data on number of insects and presence of B. bassiana are presented in Table 3. The number of insects varied greatly between treatments. The percentage of larvae killed by B. bassiana was highest at the Bruck Farm and in general the application of B. bassiana did not influence the percentage of insects killed.
Data on overwintering mortality in the 1996 plots are presented in Table 4. Data are from 2-1m² samples per treatment/replication. Numerous larvae died from abiotic causes. Most likely these insects were injured during harvest or tillage and died by infection from a saprophytic organism. Because of limited data no statistical analysis was performed. There is, however, no indication that a post-harvest application of B. bassiana increased the number of mycotic larvae in treatments within a location except at the application on the McLaughlin Farm.
Efficacy of B. bassiana, application in 1997, is presented in Table 5. A statistically significant reduction in number of tunnels between treated and check plots was recorded at the Eldora and Panama locations. Correspondingly there were significant differences in length of tunnels between treated and check plots at Eldora and Panama. There were also statistically significant differences in cm of tunneling at the Hampton (18% reduction) location, however not as great as those at the Eldora (49% reduction) or Panama (52% reduction) locations. A reduction in number of tunnels indicates fewer larvae entering the plant. This is a general trend throughout the 1997 study. There were no significant yield differences between treatments at the Hampton, Eldora or Cumming locations. There was, however, a statistically significant increase in yield at the Panama location. Yields at the Panama location were taken from 1600 row ft of corn, whereas, the yields at the other locations were determined from 44 row ft. Measuring yields from a larger area most likely reduces variability caused by plant spacing and size of individual plants. Yield samples from a larger area in all trials may have shown significant yield increases in the B. bassiana treated plots.
B. bassiana is an indigenous organism which currently contributes significantly to killing ECB larvae. The current research documents that indigenous inocula can be augmented reducing damage to corn caused by ECB. Commercial products based on B. bassiana have the potential as an alternative to present management components for the ECB. B. bassiana is environmentally compatible and thus when used as an alternative to chemical insecticides will contribute to increased environmental quality.
This is the first on farm research to evaluate B. bassiana as a suppressant of ECB. It was one of the first public evaluations of a biologically-based product for management of ECB. Adoption of B. bassiana as a management tool is dependent on federal approval of B. bassiana for ECB management. Application for registration will be initiated in the near future.
Involvement of Other Audiences
Three field days were held in 1996, two in 1997. Area farmers, reporters and other interested parties attended numbering between 25 and 75. Many questions were answered about product safety, efficacy, mode of action, and availability.
Educational & Outreach Activities
These data and data from a complimentary research project will be combined in a manuscript for submission to a referred journal. This present research was highlighted in: LyonsJohnson, D. 1997. Fungus, corn plants team up to stymie borer pest. Agricultural Research. U.S. Department of Agriculture. 45(1): 12.
Areas needing additional study
Additional research is needed on application technology, effect on yield, post-harvest application to kill overwintering ECB larvae and amount of inoculum to cause an endophytic relationship that will keep the ECB below the economic threshold.
Doberski, J. W., and H. T. Tribe. 1980. Isolation of entomogenous fungi from elm bark and soil with reference to ecology of Beauveria bassiana and Metarhizium antisopliae. Trans. Br. Mycol. Soc. 74: 95-100.
Lewis, L. C. 1982. Present status of introduced parasitoids of the European corn borer, Ostrinia nubilalis (Hübner), in Iowa. Iowa State Journal of Research 56: 429-436.
Lewis, L. C., and L. A. Bing. 1991. Bacillus thuringiensis and Beauveria bassiana (Balsamo) Vuillemin for European corn borer control: Program for immediate and season long suppression. Can. Entomol. 123: 387-393.
Ritchie, S. W., J. J. Hanway, and G. O. Benson. 1986. How a corn plant develops. Special Report 38. Iowa Cooperative Extension Service, Ames, Iowa.
SAS Institute. 1990. SYS/STAT user’s guide, vol. 2, version 6, 4th ed. SAS Institute, Cary, NC.