On second thought, I tried again and found that at 1.25 mph and 11.6 feet wide you are covering 1276 sq feet per minute. (or 118.5 sq meters). And you would be applying 1.5 ounces per 1000 sqft. At 2.5 mph you would be applying .75 ounce per thousand sqft. At 3.5 mph you are applying .64 ounces per thousand sqft.
I agree; your solution is too weak. You need about 58 ml per liter, (at 4 km/hr).