Symptoms of fertilizer burn are large patches of browning or dead grass that have a uniform, consistent pattern such as stripes across the entire lawn.
Typical problems when using a drop spreader
Excess fertilizer deposited on a lawn by a drop spreader may appear as brown rectangular spots (the width of the spreader) at the end of the lawn. This occurs when the spreader is opened from a stationary point and the initial walking process is begun. If the spreader was not calibrated correctly, too much fertilizer was deposited in those areas. Extreme cases result in the whole strip being burned. If the spreader is old, the base of the spreader corrodes and can cause an irregular hourglass pattern as the fertilizer "pills out" from the base of the machine.
Typical problems when using a rotary cyclone spreader
There is less chance to burn a lawn with a rotary or cyclone spreader unless the spreader is not calibrated correctly and too much product is used. Fertilizer granules are thrown from a rotary or cyclone spreader and dispersed over a greater area than they would be if they were simply being dropped as by a drop spreader. A consistent, uniform browning over the lawn would indicate that an inappropriate amount of fertilizer was used. Consult with the local county extension agent if you are unsure about the discoloration of your lawn.