Herbicide sprayer

After 35 years as a weed researcher I retired.  Herbicide application is in my blood and with a new zero turn mower in 2022 it was time to upgraded my home spray system from a pump-up sprayer to a self contained unit on the mower.  In theory, I wanted to be able to see the weed as I mow it off then spray it after the mower passes plus have a spray wand to hit larger patches not accessible with the mower.   I was not looking for a large broadcast sprayer but a small spot sprayer where herbicide would be applied to a specific weed patch as I mowed in a one pass operation.  

The mower deck width is 46" so ideally the spray pattern width should be 52 to 60" to allow 20% overlap of of the tapered edges of flat fan spray nozzles.   There is a structural support bar in the back of the mower 24" above the ground and ideal for attaching the boom.  

How Big and Prebuild Calculations

Flat fan nozzle charts from the Teejet catalog show xxxo1 nozzles spray 1 gallon/minute at 40 lbs pressure.  Using a sprayer width of 60" calculations form the Teejet catalog show a 2 nozzles sprayer having 30 inch spacing would need an 11 gallon tank to spray an acre of land when traveling at 3 mph.

The purpose of the sprayer is a spot sprayer and not broadcast over a large area.  Weight of sprayer filled with 11 gal would be about 100 lbs.   

The Tank, Pump and Boom

I purchased the Ironton 8 gallon ATV Spot Sprayer to serve as the base unit for my spray system.  The 12 volt pump has a flow rate of 1 GPM and working pressure of 40 psi.  It has a maximum power requirement of 3 amps.  The sprayer comes with a 11 ft hose and spray wand that provides 20 ft range (hose + spray).  

The boom width is 30" and made with a 1x1.5" piece of scrap redwood.   The ends were trimmed to make a 1" square for the nozzle body clamp.   The wood boom allows easy attachment to the mower using 6" L brackets.   TeeJet 110 degree angle fan nozzles were spaced at 26" and the 2 nozzole boom provides a 52" swath width.  

Sprayer pump is hardwired into Cub Cadet mower battery.   A larger Cub Cadet mower battery was purchased to accommodate the demands of the sprayer when the mower motor was not running during testing and cleaning.   

Spray Boom Plumbing

The 3/8" feeder line for the boom was spliced into the spray wand line just after the pump using a tee.  The feeder line has a 12 volt solenoid to turn on or off the boom.  The solenoid  is controlled with a push/pull switch mounted near the height adjust knob of the mower. 

The feeder line is attached to the boom using a tee located in the center of the boom.  The tubing feeding the nozzles is 12" long.  A heat gun was used to warm the 3/8" tubing so it would fit over the 1/2" nozzle body.  The nozzles are attached to the boom using teejet nozzle metal brackets for 1" square booms.  Zip ties are used to attach tubing to the boom.

 Parts list for spray boom

2- 3/8" nylon tees

8 - 3/8" hose clamps

6 ft - 3/8" reinforced tubing

1  ball valve (SHARKBITE Brass Barb Ball Stop Valve, 3/8 X 3/8 In. $12 from True Value Hardware) was used to shut off the boom when hand wand is used.  

2 -TeeJet XR11001VS Nozzle, Extended Range Flat Spray Tip, Orange

2 -TeeJet 4193A-5-50 screen size TeeJet Check Valve - Brass (reduces drips)

2 - 1/2" 90 degree Diaphragm check valve nozzle bodies with quick release nozzle caps

2 -6" L brackets. 

Push/pull automotive switch from Truevalue.com to turn on/off pump.  Placed near the hour meter.

Wiring and connectors

Tank Platform.

This is a test and build project so your design will be different than mine.  Ideally it should have been metal and welded to mower frame.  I chose a wood platform because it was easy to modify and adapt as needs change.  Because it is wood extra bracing is necessary to set snugly on frame of the mower.  The platform and tank will be strapped down with metal strapping to hold in place.  A 50 mm ammo box holding  dust masks, safety glasses, clean rubber gloves small empty lidded container and sprayer parts is attached to the left of spray tank.  

The wood platform is painted with a red enamel paint.   

Signage for spray area. 

Print on full 8.5x11 paper then cut horizontally  so two signs.  Fold in half and staple to wire flag.   

Sprayer calibration sheet.  

Thoughts and hacks

1. Define your spay area with warning flags before you spray. 

2. If the pump fails to prime unfurrow the wand hose and open sprayer wand to full.    

3. Wear rubber gloves and safety glasses when mixing

4. Sun glasses will help you see mower stripes better to show where you have sprayed.

5. Use a tight zero turn to align next spray strip.  

6. Mix in 5 gallon batches.  Mixing batches of 5 gallons or less allows mower to agitate the mixture when mowing rough ground. 

7. Use boom as much as possible for even distribution of herbicide.  Wand is great for places where mower cannot go but uses herbicide at a 2x rate when compared to boom.  

8. Check for skips 2 weeks after spraying.

9. Dry flowable (df) herbicides plug nozzles because of the lack of agitation and the suspension settles out.   Drain tank and rinse after DF use.  Do not store DF in tank because it just gums up the pump and nozzles.    

10. Used 1 or 2.5 gallon containers to store unsprayed herbicide.  

Video 

My youtube video showing the sprayer in action is at https://youtu.be/ZMe3rGv1P28?si=cSC3A2I1nWcz6nnj