Traditionally, Kansans have applied crabgrass preventer when the redbuds bloomed.

"Unfortunately, that rule of thumb applies only if you’ve got a native redbud, growing wild," said Fagerness, a Kansas State University horticulturist. "As a result, many Kansans have been applying preventers after the year’s crop of annual weeds have germinated. So, the herbicides haven’t worked."

Preventers will work statewide, however, if applied as soon as established lawns green up and start growing well. In most of Kansas, that means by April 1 – or, in cool zones, by April 15.

Fagerness prefers that homeowners apply their lawn’s annual crabgrass control in half-doses, applied eight weeks apart.

"That can be particularly helpful for cool-season lawn turfs," he said. "Tall fescue and Kentucky bluegrass sort of shut down in Kansas’ hot, dry summers. That can be a real window of opportunity for any weeds produced following your first application."

Whether applied all at once or in two half-doses, however, pre-emergence herbicides can provide good control only if applied thoroughly and evenly, following label directions, Fagerness advised.

Exceptions that should receive no crabgrass preventer this year are new lawns (i.e., those that haven’t merited mowing at least three times since planting) and established lawns treated last fall with a fertilizer-Barricade combination. MANHATTAN, Kan. -- Turfgrass specialist Matt Fagerness wants April Fools Day to take on a new meaning in Kansas: the deadline for applying crabgrass controls.

Traditionally, Kansans have applied crabgrass preventer when the redbuds bloomed.

"Unfortunately, that rule of thumb applies only if you’ve got a native redbud, growing wild," said Fagerness, a Kansas State University horticulturist. "As a result, many Kansans have been applying preventers after the year’s crop of annual weeds have germinated. So, the herbicides haven’t worked."

Preventers will work statewide, however, if applied as soon as established lawns green up and start growing well. In most of Kansas, that means by April 1 – or, in cool zones, by April 15.

Fagerness prefers that homeowners apply their lawn’s annual crabgrass control in half-doses, applied eight weeks apart.

"That can be particularly helpful for cool-season lawn turfs," he said. "Tall fescue and Kentucky bluegrass sort of shut down in Kansas’ hot, dry summers. That can be a real window of opportunity for any weeds produced following your first application."

Whether applied all at once or in two half-doses, however, pre-emergence herbicides can provide good control only if applied thoroughly and evenly, following label directions, Fagerness advised.

Exceptions that should receive no crabgrass preventer this year are new lawns (i.e., those that haven’t merited mowing at least three times since planting) and established lawns treated last fall with a fertilizer-Barricade combination.