Abstract: A method that includes determining, based on data from a first sensor, a first estimated value of a crop health parameter in a first section of a crop and determining, based on data from a second sensor, a second estimated value of the crop health parameter in a second section of the crop. The method also includes measuring, using a third sensor, a measured value of the crop health parameter in the second section, and comparing the second estimated value and the measured value to determine a calibration factor. Additionally, the method includes determining a first product application plan for the first section based upon the first estimated value and the calibration factor.

Abstract: A controller for agricultural sprayers utilises a detector (23, 123, 148) to generate red, blue and green colour signals across a field of view. The colour signals are used to generate a `its green` or `not green` output to switch a spray nozzle (13) detection of something deemed to be green. The algorithm which determines if there is something which is `green`, rather than `not green`, looks at the level of green component over the red and blue components in the colour signal and if both are exceeded then the decision is that it is `green`. The level of green over each of red and blue can be compared against preset values to determine the `green`, `not green` output. The level of green can be established by summing pixel by pixel over an area within the field of view under consideration to see if the sum for the area exceeds a set level to decide that the area is `green` and requires spraying.