Self-regulating weed control through the enhancement of beneficial ground dwelling invertebrates

Self-regulating weed control through the enhancement of beneficial ground dwelling invertebrates

Summary

The second year of the proposed project was undertaken. Pitfall traps were used to access the invertebrate community and seed cards were used to determine their effect on weed seed removal for the second year. The laboratory choice study was completed. All proposed field work and lab studies are complete. The only remaining work for the project includes beetle species identification from beetles captures in 2011 and data analysis for both objectives. All work has been overseen and approved by my research committee including Dr. Robert Gallagher (cropping systems ecologist), Dr. Shelby Fleischer (agroecosystems entomologist), Dr. Jonathon Tooker (agroecosystems entomologist), Dr. Tomas Carlo (seed ecologist) and Dr. Timothy Leslie (entomologist with carabid expertise).

Objectives/Performance Targets

Objective 1: Determine if the integration of legume green manure crops into reduced tillage cropping systems will enhance the diversity, abundance and activity of the beneficial ground dwelling invertebrate community, and thereby the pest management services with respect to weed seed predation.

The second year plots were established and data was collected. All individual captures from 2010 were identified. Species captured in 2011 are still being identified. The 2010 data shows that more granivorous carabid beetles were captured in the integrated plots than the no-till or organic plots. The amount of seed predation is yet to be analyzed.

All field work for objective 1 is complete. The 2011 beetle identification needs to be completed. Once this is done, data analyses for this objective can be undertaken. This will be complete by May 2012.

Objective 2: Determine if weed seed ‘debits’ from the soil seed bank by invertebrate seed predators are weed species specific, thereby facilitating a shift in the weed community composition.

Beetles were captured over the summer/fall via pitfall traps and are being reared in the laboratory for the second year. All proposed weed seed preference studies with Harpalus pensylvanicus are complete. Harpalus pensylvanicus was the only species abundant in the fields and therefore no other beetles were caught frequently enough to perform preference studies. However, some additional work with H. pensylvanicus was done. Seed choice experiments were done and it was observed that beetles would preferentially go to visually obscured imbibed seed vs. either visually obscured beads or visually obscured dry seeds. As such, cafeteria studies were done in which beetles had a choice of 7 dry seed species in one trial the same 7 seed species that were imbibed in the second trial. It seems possible that seed preference is different when the seed is dry versus it being wet. Some research has documented that large seeds, such as velvetleaf, cannot be eaten by beetles unless the seed is moist. The analyses of VOC’s being released from weed seeds by GCMS were completed and it was found that before germination (& when beetles would preferentially go to seed) carbon dioxide and ethylene were being released from the seed. Amounts of these chemicals released by seed were quantified for each seed species. A study with a y-tube olfactometer is currently being done to determine if beetles are attracted to either of these chemicals.

Another study was completed to elucidate the role of granivorous beeltles that was not initially proposed. Velvetleaf (Abutilon theophrastii) seeds were grown in the laboratory and marked with the stable isotope, 15N. These seeds were then distributed in a field. Beetles, and other granivores, were captured in the field in the subsequent week and analyzed to determine the amount of 15N in their bodies. The results of this will give an idea of the amount of velvetleaf seeds eaten by different species in the field. The study was also repeated with Giant Foxtail (Setaria faberi) seeds. Invertebrates are soon to be sent to a laboratory for analysis of 15N content.

All proposed work for Objective 2 is complete. The additional y-tube olfactometer study is ongoing. Data analyses for this objective needs to be completed and should be done by the end of January.

Accomplishments/Milestones

All proposed field work and lab studies are complete. The project has progressed as expected and it appears that all work will be done and written up by May 2012. It has been found that the proposed integrated plots harbor more granivorous beetles than either no-till or organic plots (in 2010). In addition, corn yields and weed abundance were not significantly different between any of the three treatments (organic, no-till, integrated). It was found that beetles can sense and find visually obscured imbibed seed. Additional laboratory and field studies were completed, as mentioned in Objectives/Performance Targets that will help to better show what weed seeds are likely to be eaten in an agricultural field. Other changes included planting soybean in year 2 rather than planting corn. It was decided that this would be the best system to promote and therefore should be the system that was evaluated.

The proposed outreach of the project was supposed to have taken place in the summer of 2011. However Penn State’s Ag Progress Days coincided with a once a year required weekly conference for my NSF CarbonEARTH fellowship. As such, I decided it best to delay the outreach to the 2012 Ag Progress Days. The benefit will be that I will have all the data from the project. Unfortunately, unless someone at PSU continues my work, I will not be able to do a field tour of my plots.

Impacts and Contributions/Outcomes

Results from 2010 show that more granivorous beetles were captured in Integrated plots. In addition, corn yields and weed density were similar among the different treatment types. The integrated no-till system is undoubtedly a more sustainable system and if current data trends hold true, it is a viable system that could save farmers money while supporting environmental health. This treatment received considerably fewer inputs than some of the others and the similar weed control result is believed to be a result of the enhancement of the ground beetle population. The results can illustrate to farmers that the potential for cheaper and safer weed control is a real possibility.

Results of the project were presented at a 2011 Penn State Graduate Research Exhibition that was open to the public. I received a first place prize for my poster and communication of my work.

• Recovered -Eaten Ragweed from Field Study
• 2011 Integrated Plot
• 2010 Integrated
• Beetle Eating Seed – Lab Choice Study

Collaborators: