Crabgrass is an annual grass considered a weed that produces a large number of small seeds that germinate in spring. Many lawns are overgrown with crabgrass. More your lawn is sparse it is more prone to rapid invasion by crabgrass especially during a hot dry summer because heat reduces the growth and stimulates the lawn of crabgrass to produce much seed to germinate in next spring. In addition, drought yellowing lawn of C 3 photosynthesis greens but crabgrass is a plant of C 4 photosynthesis. Increase the mowing height, correct the pH of the soil, aerate the soil, reduce the thatch to thick and fertilize properly. But above all, always mow and pick up the scraps that contain a large number of crabgrass seed that will germinate the following spring. In other words, if we do not collect grass clippings, we replant crabgrass each mowing. According to the percentage of crabgrass in your lawn, it may be necessary to aerate the soil, add grass seed followed by topdressing and fertilizing to promote grass growth at the expense of crabgrass.