Mild weather causes soil temperatures to heat up and leads to weeds popping up in area landscapes. Herbicide applications to prevent the germination of weed seedlings is linked to soil temperatures and treatment time can vary from Mid February to March 1.

Before shopping for an herbicide, identify the weed and determine why the weed has become a problem. Perhaps the area is in heavy shade and the grass can't compete with the weeds, or the dogs and/or kids play in the area and the soil has become compacted. Are you mowing at the correct height and removing no more than one-third the height or perhaps the grass is stressed from too much water due to over-irrigation? A healthy lawn can keep weeds from becoming established but this involves following good cultural practices. Examine mowing, water and fertilization practices to combat weed problems.

Identify the Weed: To have any success at controlling weeds, it is critical that they be identified and grouped into one of these three categories: broadleaf, grasses, and sedges.

Broadleaf weeds have leaves with netted veins and often have showy flowers. Examples include dollarweed, chickweed, Florida betony, clovers, spurges, Asiatic hawksbeard and many others.

Grass weeds have leaves with parallel veins and have hollow, rounded stems with nodes referred to as joints. Flowers are composed of seedheads that lack petals so are not as showy as broadleaf weeds. Examples include crabgrass, torpedograss, goosegrass, sandspur, carpetgrass, Alexandergrass, etc.

Sedges have triangular stems, are solid (not hollow), and have no nodes. Flowers are often used to help identify the type of sedge. Seed heads are often spiky structures with short leaves just beneath the seed heads at the top of a stalk. Examples include purple nutsedge, yellow nutsedge, globe sedge, and annual kyllinga.

Weed Control: If a commercial Pest Control Company services your lawn, they have access to a wider arsenal of materials for weed control. Never apply another herbicide to your lawn after a professional service has treated because it can damage your lawn.

Herbicides will help control weeds but will also weaken grasses in the treated area. Tree roots that extend into treated areas will absorb herbicides and if used repeatedly may cause stress to trees. If weeds start in a small area, the first defense should be to hand-pull. If weeds are impossible to pull by hand or the affected area is out of control, apply an herbicide to the weeds including a ten to fifteen foot buffer area. When selecting an herbicide, read the fine print on the label to make sure it's safe to use on your lawn and will control your specific weed problem. Now is not a good time to apply weed and feed products because it's too early to fertilize lawns. Wait until March to apply a good quality fertilizer to lawns.

Herbicides are divided into two groups: preemergent and postemergent herbicides. Preemergent herbicides are applied to prevent weed seeds from germinating whereas postemergent herbicides are used to control existing weeds. Benefin (Hi-Yield Benefin Granular, Balan) is a good preemergent material to control grassy weeds safely on most home lawns. Atrazine products have both pre and postemergent properties and are safe for use on St. Augustinegrass to control many young broadleaf weeds.

Sedges are difficult weeds to control and are often found in soils that are moist and compacted. Control with herbicides should be in conjunction with correcting the drainage or soil compaction problems. For chemical control, use Basagran to control yellow nutsedge and Manage or Image to control purple nutsedge. Repeat applications will be necessary for control because of the underground structures. Image slows down lawn growth so should not be used now when lawns are recovering from the winter.

For hard-to-control existing weeds, try using a two or three way mix containing 2,4-D, MCPP, and/or Dicamba such as Spectracide Weed Stop, Bayer Advanced Lawn Southern Weed Killer, or Ortho Weed B-Gone for lawns. Read the label and make sure it's safe to use on your specific variety of lawn. 'Floratam', a commonly used variety of St. Augustinegrass, is often excluded from the label.

Crabgrass is prolific and is a tough weed to control with herbicides. Preemergent herbicides are only effective if the weeds die back and are germinating from seed. A newer product on the market for crabgrass control is AgraLawn Crabgrass Control. One of the main active ingredients is baking soda but this product combines other ingredients like cinnamon, corn and wheat flour and claims to be less toxic than straight baking soda. For control, apply to green leaves of the crabgrass when dew is on the grass or mist lightly before application. Do not treat if rain is predicted. Expect some damage to the treated lawn area.

Some weeds are almost impossible to control with traditional lawn herbicides and will require more drastic measures. A broad-spectrum herbicide such as glyphosate is another option to control tough weeds like crabgrass, bermudagrass, Virginia buttonweed, Florida betony, alligator weed, and doveweed in St. Augustinegrass. This will kill everything, including St. Augustinegrass. Use an edger or shovel to cut the runners of the St. Augustinegrass around the area to be treated. Glyphosate is a systemic herbicide and cutting the runners will prevent the material from being transferred outside of the treated area.

To increase the effectiveness of an herbicide, water the day or evening before treatment or time the application after a rainfall. Timing is everything: it's easier to control young weeds versus mature, established weeds. For more information on weed control, call our office for the publication Weed Management in Home Lawns or look for it on the Internet at http://edis.ifas.ufl.edu/EP141.

For help with weed identification, take the weed to your local county extension office or to a retail garden center. Another option is to purchase a book with great colored photos produced by the University of Florida called Weeds of Southern Turfgrass, SP 79. This book sells for $8.00 plus shipping and handling. Another great book to help with lawn management is the new Florida Lawn Handbook, SP 045 available for $19.95 plus shipping and handling. Both books can be ordered by calling 1-800-226-1764.

By Terry Brite DelValle, Duval County Environmental Horticulture Extension Agent