Other Efforts to Improve Air Quality

Includes information on truck updates, engine retrofits, dust control, and more. 

  • Truck Upgrades: Walnut growers have been upgrading diesel trucks. Heavier trucks were retrofitted with PM filters beginning January 1, 2012. Older trucks’ engines will be replaced starting January 1, 2015. By January 1, 2023, nearly all trucks will need to have 2010 model year engines or equivalent.
  • Diesel Engine Retrofits:  Walnut growers/processors are retrofitting self-propelled diesel equipment 25 horsepower or greater such as tractors, harvesters, sprayers, forklifts and all-terrain vehicles to reduce diesel emissions, including particulate matter (PM 10) and other pollutants.
  • On-farm Dust Control: Practices such as mowing in-season cover crop and increasing use of pre-emergence and selective post emergence herbicides are economic and eliminate need to cultivate, mitigating dust generation.
  • Harvest: Walnut growers strive to reduce dust at harvest. One harvesting equipment company has developed a mechanical harvester for walnuts that traps most dust by drawing it through a polyurethane brush (see Fig. 3). A stream of water causes dust to form into tiny “mudballs” falling harmlessly to the ground. Such machines are starting to be used in walnut orchards where, in combination with other practices, have reduced dust by 30 to 40 percent compared to 20 years ago.
Fig. 3. Dust reducing harvester for walnuts 



  • Air Quality Districts: These have worked with the walnut industry on dust-control harvest measures including: smoothing orchard floors before harvest, tweaking fans and other parts on harvesting machines, and aiming dust away from roads and homes. If time is not an issue, harvesters also slow down to generate less dust.
  • Ranch Roads: Many walnut growers now treat their ranch roads with sand, decomposed granite, or proprietary dust mitigation products (see Fig. 4).


Fig. 4. Ranch road dust mitigation.


  • Wood Smoke Pollution: Orchard wastes (prunings, removed trees etc.) are no longer burned. These are shredded in the orchard (see Fig.5) improving both air and soil quality.
Fig. 5. Tree removal and shredding walnut prunings