Eugene, A crop that has been pollinated is indicated in several manner. 1. The falling of the petals of the flower. (Canola) 2. A relative change in position the flower head before and after pollination. (Clover) 3.Change in tissue condition of reproductive parts of the flower - shriveling of stamens/ stigma. (Fruit) 4. Change due to "tripping of the flower. (Lucerne) A grower I presume like a beekeeper with his or her bees has "the eye" and experience, so after looking around leaves the field "happy with the set" or not depending what has been seen. Peter