Things You'll Need
Lawns can have all kinds of problems, including insects that eat away at grass blades or invasions from fire ants. Lawns also need care in most locations to stay green and healthy. To solve these issues, you can use insecticides and fertilizers together at the same time and do half the work.
Measure the area of lawn to be treated to find the square footage or yardage. This can be a rough guess. There is no need to break out the measuring tape. You need the measurement to determine how much of the chemical to use. Usually stepping it off will do.
Check the instructions on both the granule insecticide and the granule fertilizer. It gives quantities of chemicals needed based on the size of the lawn. Determine how much you will need of each.
Measure out the amounts of each of the chemicals needed and place them in separate buckets. This way if you mess up or lose count, you won't have already mixed the two together, and you can start over. Once you have the quantities needed, pour appropriate amounts of insecticide and fertilizer into the third bucket and mix thoroughly.
Pour the mixture into a spreader and adjust the dial to spread at the rate recommended. If the fertilizer and insecticide have a different rate, you can split the difference as long as it won't increase the fertilizer. You don't want more fertilizer on your lawn than it should have, as this can cause damage. If splitting the rate would increase the fertilizer output, then just use the fertilizer rate.
Spread the mix in a crisscross pattern over the lawn until you have used all of the mix.
Consider wearing gloves while working with chemical insecticides and fertilizers.