ECOLOGICAL WEED MANAGEMENT: THE ROLE OF GROUND BEETLES IN WEED SEED PREDATION
Open Access
- Author:
- Ward, Meredith Jo
- Graduate Program:
- Agronomy
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- William Curran, Thesis Advisor/Co-Advisor
- Keywords:
- biological control
beetle
management
weed
Ecological
seed predation - Abstract:
- Weed management in cropping systems is a constant challenge for farmers. Crop-weed competition causes an overall crop yield loss of 12% annually, costing farmers around $15 billion dollars. Conservation of weed seed predators may help reduce weed infestations. This practice consists of enhancing populations of natural biocontrol agents that helps limit weed abundance. Ground beetles are one such biocontrol agent. Harpalus pensylvanicus and Amara aenea are omnivorous ground beetles that occur naturally in Pennsylvania and in the Northeast. These beetles are known to feed on weed seeds of species frequently found in Pennsylvania farm fields. Successful integration of seed predation as a weed management practice requires the incorporation of “suitable” cropping systems at specific times throughout the growing season. By evaluating seed preference, beetle activity density and their relationship to crop phenology and timing of weed seed rain, the importance of weed seeds as a food source to H. pensylvanicus’ survival and its potential impact on weed seed abundance and weed management can be assessed. This study investigated the 1.) feeding preference of H. pensylvanicus when presented with three common summer annual weeds and its preference for fresh and aged giant foxtail (Setaria faberii Herrm.) seed, 2.) H. pensylvanicus and A. aenea activity density and seed predation in six cropping systems, and 3.) measured giant foxtail seed rain and evaluated the coincidence of giant foxtail seed rain with H. pensylvanicus activity density. Weed species seed preference experiments were conducted using giant foxtail, common lambsquarters (Chenopodium album L.), and velvetleaf (Abutilon theophrasti Medikus). The seed age preference experiment focused on fresh and field aged giant foxtail seed. H. pensylvanicus consumed giant foxtail and common lambsquarters seed, but not velvetleaf seed. When given a choice amongst the three weed species H. pensylvanicus preferred seeds of common lambsquarters and giant foxtail equally over velvetleaf seed. H. pensylvanicus consumed both newly dispersed and field aged seeds but when given the choice, preferred newly dispersed seed. This result indicates H. pensylvanicus would likely target newly dispersed weed seed rather than older seed in the seed banks. The activity density of Amara aenea (DeGeer) and Harpalus pensylvanicus (DeGeer) was monitored during the summers of 2004 and 2005 in five cropping systems and sweet corn (Zea mays L.) having different crop species and levels or timing of soil disturbance. Seed predation was assessed from June to September in three of the five cropping systems in 2005. In 2004, A. aenea had peak activity density in the beginning of July in a brassica/buckwheat/brassica cover crop rotation. A. aenea was not detected in 2005. H. pensylvanicus activity density peaked in early August both in 2004 and 2005. H. pensylvanicus activity density was unaffected by cropping system early in the summer; however, soil disturbance in the five cropping systems may have influenced beetle activity density in the fall. Cropping systems with little to no soil disturbances had equal or greater activity density than frequently disturbed treatments. This suggests that H. pensylvanicus may not tolerate one cropping system better than another, but may tolerate specific crop types or practices during specific times of the year. Results from the sweet corn (which followed the cropping systems) suggest that the previous year’s crop may not negatively affect activity density in that field the following year. Seed predation rates in the two cropping systems averaged between 38 to 63% and rates in the sweet corn averaged between 38 to 61%. Peak seed predation rates in the two cropping systems occurred in early spring and in August while peak seed predation in the sweet corn peaked towards the end of July. Giant foxtail seed dispersal was evaluated by seeding on four dates approximately 10 days apart from mid May to mid June and measuring dispersed seed from August through October. H. pensylvanicus activity density was monitored using pitfall traps in foxtail plots over a 72h period. Sampling occurred from June to October. Dispersed seed was quantified every 10 to 14 days and beetle activity density was monitored on 72 hour intervals. In 2005, giant foxtail seed rain began in mid August and ended in late October. The total amount of seed collected over this period averaged between 12,000 and 18,000 seeds/trap. Peak seed rain occurred in early October at the two locations. In 2006, seed rain began in late August and did not peak until the Oct. 19 collection, then quickly declined. H. pensylvanicus was most abundant in August. In the foxtail plots in 2006, beetle activity density was more constant with a spike in late August with fewer beetles captured in October and none in November. H. pensylvanicus activity density does not appear to have coincided with the production of giant foxtail seed in Pennsylvania. Other research has suggested large crabgrass (Digitaria sanguinalis) and fall panicum (Panicum dichotomiflorum) may be better candidates (Brust, 1994) as well as yellow foxtail (S. glauca) (Curran, unpublished).These findings suggest that giant foxtail seed may not be a key food source for the survival of H. pensylvanicus in the Northeast, especially in tilled cropping systems. However, H. pensylvanicus may prefer and may have coincided with other annual weed lifecycles. Additional research should focus on the phenology of weeds and the timing of weed seed rain in relationship to this and other potential weed seed predators.