Conclusion

The optimum bee population for a given field is one that results in 1 - 4 flowers remaining open on racemes at the end of the day

Slide 13 of 17
Notes:

Thus, I hypothesize that the optimum bee population for a given field is one that results in 1 - 4 flowers remaining open on racemes at the end of the day. If all flowers are pollinated every day, or if more than 4 flowers are accumulating, then seed set may be less per pod than maximum. Bee populations are not optimal for the flower resources.

I have found that the distribution of open flowers per raceme at the end of the day varies from day to day in a given field, depending on the temperature that day. On warm days there is more time to forage, and perhaps the bees are moving faster or more of them are foraging, so there are likely to be few open flowers still available at the end of the day. On cooler days more flowers remain available at the end of the day. So the optimal bee population varies with temperature. Still, a grower can get a good feel for how many bees he needs on his field by monitoring flowers per raceme at the end of the day during the first two to four weeks of bloom.

One risk not included in this rule of thumb: the longer the flowers remain open without being tripped, the greater the opportunity for lygus bug and other flower pests to damage the flower.