The controller receives the actual application rate from the monitor and continuously compares it with the pre-set desired rate. Most of these automatic control monitors combine the characteristics of the first two types of monitors discussed earlier. Because of that they are usually more expensive. Some automatic control monitors may be operated in manual mode with a flip of a switch for spot-spraying where you may want to apply chemicals at more or less than the recommended rate. Marker systems are popular, especially among farmers doing custom spraying with large booms.
Markers reduce skips and overlaps by indicating where to drive on each pass.
Most markers systems use foam or dye. Markers by abe continuous but are usually intermittent - about every 25 feet. The foam or dye requires a separate tank and mix, a pump or compressor, a delivery to each end of the boom, and a control to select the desired boom end. No endorsement is intended by Iowa State University Cooperative Extension Service of companies or their products mentioned nor is criticism implied of similar companies or their products not mentioned. Many pesticides are so toxic that exposure to even a small amount can kill and adult.