- Getting Rid Of Crabgrass
Perhaps the most spectacular use of chemicals for weed control on home properties is pre-emergent weed killer which will prevent and control crabgrass in lawns.
Five materials are fairly available, each with certain advantages and disadvantages. These are calcium arsenate, chlordane, dacthal, lead arsenate and zytron. Two of them, calcium and lead arsenate, are also controls for three other lawn weeds - knotweed, common chickweed and annual bluegrass (Poa annua).
A common impression is that these pre-emergent chemicals control crabgrass by killing the seed before it germinates. This is not the case. If it were, a single application would eradicate this weed for years, since there would be no viable seeds left to produce plants. Actually all of these chemicals work by killing seed immediately after it sprouts and as the seed coat splits. Calcium and lead arsenate kill by "waiting" until the germinating seed has exhausted its extremely small store of phosphorus and sends out its minute new roots to take up a replacement supply of this element from the soil; the arsenic substitutes for phosphorus and kills the tiny plant. Chlordane works by poisoning the root runner as it starts to make growth, checking any further development of the plant.
Solutions of all these chemicals can be applied to dormant crabgrass seed but if the chemical is washed off before the seed coat splits, a normal seedling will develop.
Signs Of Germination
These chemicals control crabgrass by building up a toxic layer an inch or so deep on the surface of the lawn. To work effectively all must be in place before crabgrass seed germination begins. Calendar dates for germination are notoriously unreliable because of the variation between seasons. Instead, use natural signs which appear when a certain number of degree hours have accumulated, not when a certain date appears on your calendar.
Here are some natural signs that announce the imminent appearance of the first crabgrass seedlings: Magnolia stellata dropping its petals; Magnolia soulangeana in flower; first buds open on French hybrid lilacs, first blooms on Darwin tulips, and apple blossoms showing trace of pink.
Pre-emergent Weed Killer and Crabgrass Control - how to use pre-emergent weed killer for controlling crabgrass.
Crabgrass Killer Strategy - my strategy from extensive post and pre-emergent testing.
What Does Crabgrass Look Like? - you can't control it if you can't recognise it.
Weed Killers - recommended chemical weed killers and the approach to using them.
Toxic Residue In Soil - it pays to be aware of not only the short term, but long term effects of weed killing products.