Managing field borders for weed seed predators
Weed seed predation could be part of an alternative weed management program for organic growers if weed seed eating organisms can be conserved and enhanced. Field border management that increases vegetative diversity is a potential method for conserving weed seed predators.
Results from predator exclusion cage studies conducted in the fall of 2011 were similar to 2010. While habitat border type did not effect seed predation, crop type heavily influences seed predation rates within the field. This seems to be due to vegetative cover. Light interception measurements were taken to confirm this.
A video camera study was also deployed in the fall of 2011. These videos showed that house mice and crickets are the predominant weed seed predators.
1.) Determine the effects four different field border vegetation communities have on levels of weed seed predation in adjacent crop fields by invertebrates and vertebrates.
2.) Identify the specific predators responsible for this weed seed predation.
3.) Disseminate the results of this project to organic growers.
Exclusion cages with seed cards were deployed in the Fall.
Similar to the previous year, broadleaf signal grass was the preferred weed seed amongst granivores. Also, habitat border treatments did not affect removal/predation rates of seeds. Instead, there were strong crop effects as well as differences between trials.
Again, in the annual row crops (corn and soybeans) seed predation was heaviest toward the field borders and dropped off towards the field center. The perennial hay crop, again, did not see this distance effect. (See Figure 1)
Late planting of the hay crop in the fall of 2010 along with a harsh winter created patchy, weedy hay fields. We plowed this and planted sorghum Sudan grass, cowpea, and forage soybeans in the Spring. This hay crop produced interesting results. Whereas the previous year's hay, consisting of orchard grass and white clover, had extremely high seed predation rates, this year's only had intermediate rates. The obvious difference between the two year's hay fields were the amount of cover each provided.
We tested this cover hypothesis by measuring crop canopy light interception in one of the fields. Results show a strong correlation between light interception (a.k.a. "shade") and seed predation. (See Figure 2)
A monitoring study using night vision cameras was deployed in the Fall of 2011. Cameras were turned on for three hours during the day and three hours at night. Analysis of the videos showed that weed seed predation occurs mostly at night. Also, the red imported fire ant, Solenopsis invicta, was not seen removing weed seeds. This is an important finding because previous studies had assumed that this species was becoming the dominant weed seed predator in the Southeast, replacing crickets and other native organisms. Instead, the videos showed that crickets and mice are the dominant weed seed predators (see videos). All seed predators seemed to prefer grass seeds over pigweed or sicklepod weed seeds.
The graduate student coordinator of this project, Aaron Fox, developed and co-led a half-day extension workshop with Charlie Plush (a graduate student in Fisheries and Wildlife Sciences)titled, "On-Farm Habitat To Provide Multiple Ecosystem Services". The workshop was presented through the Center for Environmental Farming Systems 'Seasons of Sustainable Agriculture' workshop series (http://www.cefs.ncsu.edu/newsevents/events/2011/sosa2011/sosa2011calendar.html#BIH). Over 50 people attended the event. Results from the study were presented with an emphasis on managing weed seeds.
PowerPoint available at: http://www.cefs.ncsu.edu/newsevents/events/2011/sosa2011/registration/weedpredation.pdf
- Weed seed predation and crop canopy light inteception showed a strong positive correlation.
- Broadleaf signalgrass seed predation rates showed similar trends to the previous year.
Impacts and Contributions/Outcomes
Utilizing field border vegetation to promote weed seed predation does not appear to be a viable pest managment strategy. However, increasing cover, either through delayed hay cutting or delayed tillage after grain harvest, can enhance this ecosystem service.
The invasive red imported fire ant, Solenopsis invicta, does not appear to provide weed seed predation services in the Southeast as previously thought.