Soil and Crops

Recently took my wheat crop off and now have some weeds starting to come in.  The question that I have is should I spray this fall to kill those existing weeds or should I wait until next spring and spray at that time, therefore, saving myself a spray expense.  Many of these weeds are annuals and will be around next spring.  My feilds will be planted back into spring wheat which will be flood irrigated.  Sometimes what happens in the spring you get a flush of weeds and you spray and plant.  However, if the rains don't come after you plant I have to irrigate the wheat out of the ground and if this happens I lose about 30% in yeild because the weeds robed my moisture.   Anyone a good plan of attack for this problem?