National Jointed Goatgrass Research Program

 

New Proposal-2002

 

1.      TITLE:     Characterization of Post-Dispersal Jointed Goatgrass Seed Predation

2.      PERSONNEL:     Phillip W. Stahlman, Research Weed Scientist, Anthony D. White, Research Scientist, and J. P. Michaud, Entomologist, Kansas State University Agricultural Research Center-Hays

3.      TIMELINE:         Initiation:                       June 2003

                                    Completion:                  June 2005

4.      HYPOTHESIS: Jointed goatgrass seed in spikelets lying on the soil surface is reduced more by predators compared to seed that has been tilled into the soil and ultimately reduces the jointed goatgrass seedbank in a no-till program.

5.      SUMMARY OF PROPOSAL:  Currently, little information is available regarding jointed goatgrass predation and disappearance.  To address this data gap in the biology of jointed goatgrass, an experiment will be conducted to evaluate the level of disappearance of post-dispersal jointed goatgrass spikelets.  One field study will provide information regarding the level of predation, identity of potential bird and rodent jointed goatgrass seed predators, and the effects tillage systems have on seed disappearance.  A second study will evaluate and identify potential insect predators that feed on jointed goatgrass spikelets.

6.      OBJECTIVES:

A.     Assess the level of jointed goatgrass seed bank reduction due to predation.

B.     Identify the organism that leads to jointed goatgrass spikelet disappearance.

C.     Evaluate management practices that may limit or increase predation.

7.      JUSTIFICATION:

Jointed goatgrass can persist in the soil seedbank for several years.  However, germination alone cannot account for the disappearance of jointed goatgrass.  In 2001-2002, we conducted a preliminary study to evaluate the predation of jointed goatgrass.  Data indicated that over 20% more jointed goatgrass spikelets remained as a result of predation exclusion (covered to exclude birds, rodents, and large insect predators).  Tillage systems and yearly effects were not evaluated.  Currently, little information regarding jointed goatgrass seed predation or disappearance is available.  Therefore, research is necessary to determine how much predation occurs with regards to jointed goatgrass, the accurate identity of the predator, and what effects tillage systems have on seed disappearance.

8.      METHODS:  The experiments will be initiated immediately after the 2003 wheat harvest on a Roxbury silt loam soil at the Agricultural Research Center near Hays.  Jointed goatgrass spikelets will be cleaned from recently harvested wheat seed each year.  This method will best simulate post-dispersal seed effects compared to using aged or previously buried jointed goatgrass seed.  Fresh seed is thought to be more attractive to predators than aged seed.  The experiments will be conducted over a period of two years.  Precipitation and temperatures will be recorded throughout the course of the study.

Study 1: Evaluation of Large Predators and Tillage Practices.  Sections of PVC pipe measuring approximately 30 cm in diameter and 40 cm in length will be placed into the soil (Figure 1).  Pipes will be buried in a production field with no history of jointed goatgrass.  Approximately 5 cm of the pipe will be exposed above the soil surface to inhibit horizontal movement of weed seeds over the soil surface.  A consistent jointed goatgrass density (100 spikelets/pipe) will be used for the entire experiment.  The seed lot will be evaluated for viability (Donald 1994) and dormancy prior to study initiation.

Treatment design will consist of a three-factor factorial with six replications and arranged in the field as a completely randomized block design.  The first factor will consist of years.  Treatments will include years one and two separately and another to span both years.  After year one, the single year pipes will be excavated and year two pipes reestablished.  This treatment structure will provide a means to evaluate individual and multiple year effects.  The second factor will consist of covered (plastic window screen) and uncovered pipes, allowing access or exclusion of predators to the seed source.  Uncovered pipes will be fitted with ramps on the interior and exterior to facilitate predator entry and exit.  The final factor includes placing jointed goatgrass spikelets either on the soil surface or approximately 5 cm below the soil surface to simulate a no-tillage or conventional management program, respectively.

We will collaborate with a field biologist to identify and determine the best way to monitor small mammal presence and predation.  Predation by birds cannot be done reliably on this small scale.

Periodically throughout the year, jointed goatgrass seedlings will be counted and removed from the pipe.  Care will be taken to not disturb spikelets or remove them from the respective pipe.  After one year the appropriate pipes will be excavated and the remaining seed quantified through either elutriation or sieving.  Recovered seed will be counted and compared to initial density.  Intact seeds will be evaluated for germination and non-germinating seeds will be subjected to tetrazolium (TZ) testing for viability.

Study 2: Evaluation of Insect Predators.  Due to limited access of walking insects into the PVC pipes in the previous experiment, insect predation will be evaluated separately.  Jointed goatgrass spikelets will be placed in various portions of the experimental area (not in PVC pipes) immediately after harvest.

Insect traps (12 total) containing antifreeze to euthanize the insects will be placed in appropriate positions around the jointed goatgrass spikelets to monitor insect species and population density.  Trapped insects will be collected weekly for approximately two months after harvest and identified in the lab.  If insects are suspected to prey upon jointed goatgrass spikelets, four traps will be converted to live trapping devices (no antifreeze).  Live insects will be collected daily and used in controlled feeding and preference studies to provide more accurate jointed goatgrass predation data.  Feeding studies with only abundant species will be conducted in a completely randomized design with six to eight replications using.  Insects in preference studies will be exposed to germinating and non-germinating seed.  Some insects are thought to be more attracted to germinating seed. 

9.      RELEVANT LITERATURE:

Donald, W.W.  1994.  A method of validating the tetrazolium assay for testing viability of dormant jointed goatgrass (Aegilops cylindrica) seed.  Weed Sci.  42:502-508.

10.  PLANNED TECHNOLOGY TRANSFER: The experiment will be shown and/or discussed at Experiment Field and Research Center Field Days and results made available to county, area, state and regional extension personnel for presentation at grower meetings and personnel in other states. Final results will be published in scientific publications. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1.  PVC pipes will be used to contain jointed goatgrass spikelets in a given experimental area.  Pipes will be left uncovered (left) or covered with a plastic window screen (right) to allow differential access to predators.  Uncovered pipes will be equipped with tapered ramps (not shown) to facilitate predator entry and exit.

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