RESEARCH RESULTS

Project title: On-farm management of cutworms in organic no-till corn

Investigator: Jeffrey Moyer, Rodale Institute Experimental Farm, Kutztown, PA
Project location: Kutztown, Pennsylvania

Researchers at the Rodale Institue Experimental Farm are leaders in the study of no-till organic farming systems, pursuing the advanced management of cover crops and a use of a roller crimper for cover crop suppression prior to planting cash crops into cover crop residue. The system shows promise for meeting the objectives of reducing weed pressure and subsequent tillage. However, researchers have also observed increased cutworm pressure in the system, and in this project they investigated the factors of timing and location in addition to application of OMRI-approved materials to mitigate cutworm damage. Study results point toward habitat manipulation as a more effective and economical strategy than material biocontrol inputs for cutworm management. Interestingly, the native soil fungus Metarhizium was also shown as effective in overcoming cutworm larvae.

Links: Full cutworm/corn project report to OFRF (17 pp).
Rodale Institue project article by Christine Ziegler Ulsh and Alison Grantham.

Researchers at the Rodale Research Farm collect
samples of pest populations to help evaluate
strategies for cutworm control in organic no-till
cropping systems.

PROJECT RESULTS
These study results are for the first two years (2008-2009) of a three-year field trial testing the efficacy of National Organic Program (NOP)-approved cutworm controls in an organic no-till corn system. The organic no-till system relies on leguminous cover crops rolled at corn planting to form a nitrogen-rich, weed-suppressive mat. While the rolled cover crop mat has shown excellent weed suppressive, erosion prevention, and energy- and time-saving capacities, it has also supported large cutworm populations and subsequent severe crop losses. Severe cutworm infestations reduced corn populations 34-67%. These losses noted at the Rodale Institute’s experimental farm, as well as by numerous farmers, motivated our study.

Black cutworm (Agrotis ipsilon) moths arrive in storm fronts in early spring and preferentially lay their eggs in lush cover crops, crop residue, or weeds. When temperatures exceed 50°F, the cutworm eggs begin to mature. Much like each corn variety requires a certain number of growing degree units (GDUs) to reach physiological maturity, developing cutworms also require a certain number of heat units to reach maturity (and their most damaging stage of development instars 3-5). From year to year, the timing of the peak influx, or biofix, of cutworm moth varies with the timing of weather front arrivals. Then from the biofix, heat units begin accumulating at different rates – faster for warm springs, slower for cool ones.

Cutworms are most damaging 312-430 heat units after the biofix. Generally, in eastern Pennsylvania, it takes about 30 days from the time of the biofix for the cutworm moth to mature to its developmental stage with greatest damage potential.

Objectives
This project was undertaken to evaluate several cutworm control tactics in organic no-till corn so as to reduce challenges faced by farmers and ultimately increase adoption of the biological no-till system. Our specific objectives were to conduct on-farm and on-station trials to identify effective management strategies for cutworm in organic no-till planted corn.

Methods
Cutworm Moth Flight Monitoring
Monitoring of cutworm moth flight was conducted using sticky wing traps, as well as cone traps and unitraps in conjunction with pheromone lures.

Cutworm Larvae Monitoring
In 2008, soil larvae were monitored prior to planting in late May-early June in 0.25 m2 quadrants to a depth of 3 inches for larval cutworms. After planting, surface transect monitoring was conducted weekly in 6” bands in 1 m of row per treatment plot (1m/10’x10’ plot). In 2009, surface transect monitoring was conducted weekly for cutworm moths, eggs, and larvae at both locations in three 1-m transects per plot (72 m/location/sampling event) from May 20-July 15. Both years, larvae were packed in an ethanol-glycerin solution and sent to Pennsylvania State University (PSU) for identification and analysis.

Factors, Plot Design and Replication
There were three factors planned in the study: location, planting time, and cutworm treatment. Our locations were two farms: the Rodale Institute farm in Kutztown, Berks County, PA (“Rodale”) and Kirby Reichert’s farm in Grantville, Dauphin County, PA (“Reichert”). In 2008, both farms had an “early” and a “late” planting date. At Rodale we planted on June 6 and June 16 and at Reichert’s we planted on June 12 and June 19. The planting dates were planned to capture two hairy vetch bloom stages, “early” bloom and “full” bloom at the two locations. Unfortunately, it rained all but 5 days in June of 2009 and we were only able to establish corn on one planting date at each location, at “full” bloom stage. In 2009, Reichert’s corn was planted on June 10 and Rodale’s corn was planted on June 16.

After each planting date, we delineated plots for 4 replicates of the six OMRI-approved cutworm controls and an untreated control. In 2008, all 112 plots were 10’ by 10’. In 2009, all 48 plots were 10’ by 20’. In 2008, we applied treatments at prescribed times ranging from planting to post-emergence. In 2009, since cutworms were artificially seeded, treatments were applied one week later and prior to corn planting at both locations. Since we needed to apply some treatments in an aqueous solution, all plots received 2 gallons of water or solution.

The OMRI-approved cutworm treatments tested were (refer to full project report for application rates):

• Dipel-DF (Valent)                                                                          
  
• Diatomaceous earth (2008 only)                                                
  
• Entrust ® (Dow AgroSciences)                                                   
  
• Ecomask (BioLogic Company)                                                    
  
• Steinernema riobrave (Barbercheck lab – lab reared)              
  
• Scanmask (BioLogic Company) (2008 only)                            
  
• Mycotrol (BioWorks)                                                                      
  
• None (water only)     
  

Cutworm Larvae Incubation and Application
Due to extremely low pest pressure in 2009, 10,000 cutworm eggs were ordered from Benzon Research in Carlisle, PA on 5/21/09. The eggs arrived on 5/28/09, were incubated at  29°C and 50% humidity until 6/1/09, when >90% of larva appeared to have hatched and were evenly applied in corn cob meal via Davis Applicators to a) the Rodale Institute (8AM); b) Reichert’s (6:30 PM).                                                                

Project Results
Pest Pressure – Moth Trapping
Overall, most moths arrived on hilltops (59% or 305/514) in May (82% or 420/514). There were significantly more moths caught in 2008 (488 moths) than in 2009 (26 moths). In 2008, the largest influx of 20 or more moths, or biofix, of cutworm moths arrived at the Rodale site on May 8, 2008 (29 moths). Based on 2008 GDUs, the subsequent time of greatest corn plant damage would have ranged from June 6 or June 7 through June 11 or June 13, 30-38 days after the biofix. Therefore, the planting dates, and subsequent dates when the corn plants would have been vulnerable (after June 16) did not coincide with the dates when the cutworms were in their most damaging stages (June 6-13). There was no biofix of moths in 2009 – the most moths caught in a night was 4.

The pheromone traps were much more effective than the sticky traps (used in 2008) or the unitraps with pheromone lures used in 2009 capturing moths. On May 8, when pheromone traps captured 20, 18, and 11 moths at the 3 respective trapping locations, we found no cutworm moths in any of the sticky wing traps. Additionally, we observed birds eating insects from the sticky traps, but not from the pheromone traps. Therefore, sticky wing traps were not utilized in 2009 and another less expensive trap, a unitrap with a pheromone lure, was used. The unitraps were not effective even when augmented by adding soapy water to the trap – not a single cutworm moth was caught in a unitrap.

Pest Pressure – Cutworm Larva
In 2008, we observed very few cutworms in our in-row cutworm larva surveys (0-3 cutworms per meter, mode of 0, Figure 2). Cutworm treatments did not affect the number of cutworms observed. Location did significantly affect the number of cutworms we observed. We observed significantly more cutworms at Reichert’s farm than at Rodale. There was also a significant interaction effect between location, cutworm treatment, and planting time. We also detected a marginally significant  negative correlation between the number of cutworms observed and the damaged corn, indicating that cutworms were not the primary cause of the observed corn plant injuries.

Pest Pressure/Soil Biological Properties – Lab Efficacy of Treatments
Since field populations were so low in both years, lab incubations of Lepidopteran larvae with field applied biocontrols (nematodes and Mycotrol) were used to assess potential treatment efficacy. In both years, it appears that the treatments were unsuccessful in infecting or killing larvae bait and that most incubated larvae were killed by a native soil fungus, Metarhizium anisopliae. Thus, it appears that the applied treatments are not as effective as a native soil pathogen in overcoming cutworm larva.

Stand establishment was about 75% of the seeding rate overall, resulting in slightly lower than ideal populations in most treatments (range: 17,500-35,000; grand mean: 26,034). Stand establishment was not correlated with metrics of cutworm pest pressure nor was it affected by cutworm treatment. In 2008, we observed extensive bird grazing on corn seedlings at Rodale and attributed sub-optimal corn populations to bird predation. In 2009, we observed extensive seed molding and failed germination in the flooded seed furrows at Rodale and anecdotally attributed poor stand establishment there to poorer site drainage and extremely wet weather.

Conclusions
The most interesting finding of this study was the distribution of the pest pressure and its implications for pest management in organic systems. A greater proportion of cutworm moths were caught in traps on unprotected hilltop sites compared to lower elevation sites bordered by buffer habitat (see addenda photos). Since this pest moves in on storm fronts, land management strategies that physically protect production fields, such as treelines, may offer cutworm management services. In addition to physically blocking pest influxes, treelines and other buffer strips provided important habitat for birds that were frequently observed catching insects or eating insect larva from the ground at both sites. These large communities of natural pest managers, while frustrating to the objectives of this project, may provide greater promise to organic producers considering this production system rather than the economically prohibitive biocontrol treatments tested.

A final report describing the results of this project is was submitted in February 2010.