Scotts WeedEx Prevent with Halts prevents crabgrass and other problem weeds for a beautiful lawn all season long. In early spring, apply when the lawn is dry to prevent the germination of crabgrass, foxtail, spurge, barnyardgrass, fall panicum, and oxalis. Apply in the fall (August-October) to prevent moss (except in California), or to prevent the germination of Poa annua, henbit, corn speedwell, and chickweed. Manufacturer recommends using a spreader to apply this product. For Scotts broadcast/rotary spreaders, use a setting of 2. For Scotts drop spreaders, use a setting of 4. For ScottsWizz, use a setting of 3. Rain, snow, or freezing weather after application will not affect performance. This product controls crabgrass in its early stages of growth. It does not control mature crabgrass and other existing weeds.