SiteSpecific Weed Management

1
Site-Specific Weed Management
2
Weed Population Characteristics

• High inter- and intra-field variability
• Populations tend to be located in patches,
  especially
• Perennial weeds
• Fields with low weed pressure

3
Weed Population Characteristics

• Patches change size and density from year to
  year, but location is stable
• Local aggregation is stronger in minimum tillage
  systems
• Patches are strongly influenced by source
  locations

4
Spatial Management Strategies

• Soil properties
• Historic information
• Real-time sensing

5
Soil Properties

• Broadcast application, but herbicide rates based
  on soil properties and label
• pH
• texture
• organic matter
• No use of weed distribution

6
Historic Information

• Spatial pattern of weed densities is mapped
• Herbicide application rates are based on
  population density and location

7
Weed Assessment Techniques

• Outline weed polygons
• Grid observation and interpolation
• Record at harvest
• Remote sensing

8
Real-time Weed Sensing

• Reflectance sensors that detect green biomass
• Image processing systems that recognize weed
  species

9
VR Herbicide Techniques

• Real-time spot sprayer
• Map-based application
• VR ground sprayer
• herbigation
• aerial (limited to on/off)

10
Benefits of SSWM

• Reduced herbicide cost
• 30-80 less material applied
• Reduced chemical in runoff water and sediment

11
Limitations of SSWM

• Cost of mapping weed populations
• Assessment difficult in seedling stage
• Limited knowledge about affect of long term spot
  spraying on weed ecosystem

12
SSWM Considerations

• Base pre-emergence applications for control of
  annuals on soil properties
• Spot spraying should be considered for fields
  with low weed problems

13
SSWM Considerations

• Use patch outlining or combine mapping to record
  weed escape areas
• Spray known weed patches plus boundary area
• Post-emergence foliar action herbicides used with
  reflectance sensors

14
SSWM Considerations

• Economic feasibility greatest for high cost
  herbicides used on problem weeds with high
  aggregation

15
Examples

• Weed Site-Specific Management

16
Site-specific weed control in German winter wheat

• Based on weed distribution determined on 20x24m
  grid
• GPS-based VR sprayer
• Potential of 40-50 reduction in herbicide

Gerhards, et al., 1997, J. Agron. Crop Sci.
178219-225
17
Simulation of herbicide use based on weed spatial
distribution

• Broadleaf and grass distributions in 12 corn and
  soybean fields in Neb.
• Postemergence herbicide based on economic
  thresholds
• Scouting for density maps must be continuing
  process
• Potential 30-72 reduction of chemical if in-row
  discrimination possible

Johnson, et al., 1995, Weed Research 35197-205
18
Light-activated weed sprayer in TX High Plains
cotton

• Weed control similar to conventional
• 56-85 reduction in herbicide applied
• High cost of system - 38,000 for 8 row sprayer

Source P. Dotray, 2000, http//precision
agriculture.tamu.edu