Preemergent Herbicides for Killing Crabgrass: When to Apply
To get rid of crabgrass it helps to know its life cycle. When spring soil temps (at a depth of 2″-3″) reach 55-60 degrees Fahrenheit, the first crabgrass seed will germinate. From mid-summer to fall, crabgrass produces seed. The crabgrass plants (but not the seeds) are killed by frosts in autumn.
Pre-emergent herbicides come in either granular or liquid form and kill crabgrass seedlings as they germinate. If you are going to core aerate or dethatch your lawn after applying pre-emergent herbicides, these ACTIONS WILL BE FOR NOT. Aerate lawns beforehand, instead.
Pre-emergent herbicides kill crabgrass at a specific time: before its seedlings emerge. Successfully getting rid of crabgrass in this manner, timing is essential. Apply pre-emergent herbicides before germination, but not too far ahead. Crabgrass germination coincides approximately with the blooming of the lilac bushes.
Types of Pre-emergent Herbicides for Killing Crabgrass
*Dimension (active ingredient, dithiopyr) is safe to use on most lawn grasses (check label first) and provides long-lasting coverage — an important consideration, since not all crabgrass seed germinates at once. Thus Dimension will kill later-germinating crabgrass, too. Dimension also displays some effectiveness as a post-emergent herbicide.
*Tupersan (active ingredient, siduron) is worth mentioning because, unlike other
pre-emergent herbicides, it will not damage germinating lawn grass seed. In fact, its active ingredient is often combined with starter fertilizers. Alternatively, for newly-seeded lawns, wait until after 3 mowings (or 3 months, to be on the safe side) before applying pre-emergent herbicides.
Using Pre-emergent Herbicides for Killing Crabgrass:
*Irrigate afterwards: water activates pre-emergent herbicides.
*Re-apply pre-emergent herbicides, if you question your product’s coverage. Because
crabgrass seedlings do not all germinate at once, re-application can kill some of the
*Follow label directions and apply the proper rate. Measure the lawn area and calibrate your spreader carefully.