PPDL Picture of the Week
December 13, 2019
Bare Spots in the Lawn Left Behind by Summer Annuals
Glenn Hardebeck, Turfgrass Research Center Manager, Purdue University, Horticulture and Landscape Architecture
With the first few frosts of the fall, summer annuals such
as crabgrass, knotweed, black medic, and spotted spurge came to the end of
their life cycle. By now these weeds
have long since desiccated and are crumbling away leaving behind bare spots in
the lawn. Properly dealing with the bare
spots is the first step to controlling next year’s weed problem.
We often look at weed problems from the wrong
prospective. Instead of seeing the weeds
as the problem, we should be looking for the problems that caused the weeds. For example, low mowing height and poor
fertility reduces turfgrass vigor and therefore increases weed pressure. Weeds don’t necessarily choke out the lawn. Instead, weeds take advantage of a weak, thin
lawn. A thick, healthy turf is the best
form of weed control. It’s important to
access a lawn in the fall and determine how to promote density. While fall fertility is the primary means to
revitalize most cool season turfgrass stands, thin lawns can still be improved
before spring through dormant overseeding.
Although early fall is the best time to overseed, it
requires the use of a power overseeder or power rake capable of slicing through
the turf to ensure good seed to soil contact.
Dormant overseeding during winter is better than waiting until spring
and it’s the easiest time to seed. During
winter, freeze/thaw cycles work to plant the seed for you without the need for
a power overseeder. Finally, it is
important to avoid treating dormant seeded turf with crabgrass preventer next
spring since it will also control the turf seedlings. For more information check AY-10: Control of
Crabgrass in Homelawns and AY-13: Lawn Improvement Programs at
https://mdc.itap.purdue.edu/