Crabgrass starts to grow in the spring . New plants can continue to germinate until the early fall. From mid-summer to fall, crabgrass produces seed. The crabgrass plants die out in the mid to late fall, leaving lots of seeds to start the cycle again in the spring. So how do you get rid of it? Well timed preemergent herbicides are the most effective way to eradicate this difficult weed.
Preemergent herbicides come in either liquid or granular form and are designed to kill seedlings before they emerge. Timing is important in order for them to be successful. Apply a preemergent before germination, but not too far ahead ( a little early is better than late). For crabgrass this is when the soil temperature reaches about 55-60 degrees F. Within a week or so of theses temperatures, crabgrass plants start to grow.
Two options for for crabgrass control are Tupersan (siduron) and Dimension (dithiopyr). Dimension is safe to use on most bluegrass ryegrass and tall fescue. Check label first for fine fescues. Tupersan is also safe for similar grasses. Both are good preemergent herbicides and both have some effectiveness as a postemergents. Dimension controls a wider variety of weeds, but Tupersan may be a better pick for newly seeded lawns.
• Lawns should be watered after the application of a preemergent herbicide.
• While inexpensive weed & feed products may contain preemergents, they are usually in smaller amounts and not very effective
• Always follow directions on the label. Apply the recommended amount for the area that you have. Spaced out treatments are much more effective than using too much at once.
• If you plan on aerating or dethatching a lawn in the spring, do it before treating for crabgrass.
• Mow taller - weeds are much more likely to grow in places where grass is shorter and thinner than in places with taller denser grass.
• Overseed thin/bare spots in the fall. The best weed prevention is a thick stand of grass. It leaves no space for the weeds to grow.
• Pull larger crabgrass plants by hand - Most postemergent herbicides are ineffective against larger plants.