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In lawn care, win the war on weeds

When looking at our frost-burned lawns, it's hard to remember them at their lush summer peak, when the battle with weeds is at full fervor. • There's not much to be done now about the brown, but you can take steps to head off an invasion of undesirable green when the weather warms up.

Know your enemy

The first step in controlling any weed is to have it properly identified. Knowing if it is a broadleaf, grass or sedge is paramount to knowing how to control it.

Broadleaf plants generally have netlike veins in their leaves and many have showy flowers. Some examples are dollarweed, creeping beggarweed and Florida pusley.

Grasses have hollow, rounded stems and nodes, or joints, that are closed and hard. The leaf blades have parallel veins and they are much longer than they are wide. The leaf blades also alternate on each side of the stem. Some examples are crabgrass, torpedograss and sandbur.

Sedges are "grasslike" weeds but are not true grasses. Sedges have a solid, triangular-shaped stem with leaves that extend in three directions. Examples include yellow nutsedge and purple nutsedge.

Take control

There are two basic methods of weed control: physical control and chemical control. It's usually best to use a combination.

Physical weed control includes mowing, hand pulling, hoeing and mulching. Many weeds in turf can be controlled by proper mowing. In general, Bahia and St. Augustine grass should be mowed at a height of 4 inches and mowed frequently enough so that only one-third of the leaf blade is removed each time. Hand pulling can be used if there are a small number of weeds. Mulching is a good weed control method for flower beds, footpaths and other areas where there is no grass. Mulch, which smothers weeds by excluding light, should be applied about 2 inches thick and kept away from the bases of plants.

Chemical weed control is the use of herbicides. Selective herbicides control certain plant types without serious harm to other plant types. A selective herbicide might kill broadleaf plants while not harming grass plants or vice versa. Nonselective herbicides kill most plants regardless of type. Roundup is probably the most widely known and used nonselective herbicide. Other chemical controls include pre-emergent herbicides that prevent seedlings from growing and post-emergent herbicides applied to existing weeds when small.

Attack now

Annual weeds (those that sprout, grow and produce flowers and seed in one year and then die) are the most easily controlled with a pre-emergent. Some annual weeds sprout in spring, others in fall. Timing the pre-emergent for the season when seeds sprout is important.

Crabgrass is a perfect example of a summer annual grass weed that is controlled by using a pre-emergent herbicide in early spring. If crabgrass has taken over your lawn in the past, put out a pre-emergent herbicide in spring. Pendimethalin (sold as Pendulum, Pre-M, Turf Weedgrass Control, or Halts Crabgrass Preventer) provides excellent control of crabgrass and is safe at the recommended rate on mature, actively growing grass (Bahia, Bermuda, St. Augustine and zoysia). Apply this herbicide when daytime temperatures reach 65 to 70 degrees for four to five days in a row (usually about the same time that azalea plants start blooming in the spring). Plan to reapply herbicide about two months later for season-long control.

Jane V. Morse is a University of Florida Extension Agent at the Pinellas County Extension Office. Mention of commercial products is for educational purposes and does not imply recommendation or endorsement by UF/IFAS. UF/IFAS neither guarantees nor warrants the performance of any product mentioned. The user is responsible for reading and following the label.

Weeds 101

Got a weed you can't identify? Take a sample (preferably with a flower or seed head) to the Pinellas County Extension Office, 12520 Ulmerton Road, Largo. Hours are 8 a.m. to 5 p.m. Monday through Friday. Also search for help on the Internet at Search for "weeds in turfgrass" and

"preemergence herbicides" for more information.

In lawn care, win the war on weeds 03/05/10 [Last modified: Friday, March 5, 2010 3:30am]
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