And maybe our weeding bots could compare spectral reflectance:

"For weed detection in cultivated crops, two interrelated general approaches have typically been used ...The first is to detect certain morphological differences between the crop and weeds...The second general approach is based on differences in spectral reflectance...Despite the different problems encountered thus far in detecting weeds, some researchers argue that the spectral characteristics of plants are sufficient to differentiate plant species without introducing geometric complexities."

"Time is what prevents everything from happening at once" - John Wheeler