Improper fertilizer application or spreading results in "streaking", the alternate dark-and light-green stripes in a lawn. Overlap wheel tracks for drop-type spreaders. For rotary spreaders, apply the fertilizer so the wheel is at the edge of the pattern from the previous pass. Use a rotary spreader rather than a drop-type spreader for agricultural type fertilizers (10-10-10, 15-15-15, etc.) that have large particle sizes. Irrigation or rain following fertilization is important to move nitrogen off the leaf blades and into the soil. Some fertilizer/herbicide combination products should not be watered-in, so read the instructions on the label. Avoid fertilizing drought-stressed or dormant turf, or when temperatures are over 80Â° F.