Cool weather has finally arrived and venturing outside is a pleasure. Now is the time to get the landscape back into shape. Because it's been too hot to do many of the standard chores, weeds may be overtaking lawns and plant beds. Now is a good time to reclaim your landscape.
The first line of defense with weed control is to hand pull. Think of the added benefit of getting exercise while you're removing those weeds. This technique works great when there are a few weeds and if they are not deeply rooted. Anyone who has ever tried to hand pull torpedo grass knows that it's a wasted effort.
Mow lawns at the proper height. This will help shade out weeds and encourage deeper roots going into winter. Mow frequently to remove taller maturing weeds before they produce seed heads.
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 are impossible to pull by hand or the affected area is out of control, spot treat the affected area to avoid causing damage to the lawn. 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.
Herbicides are divided into two groups: preemergence and postemergence herbicides. Preemergence herbicides are applied to prevent weed seeds from germinating whereas postemergence herbicides are used to control existing weeds. Benefin (Hi-Yield Benefin Granular, Balan) is a good preemergence material to control grassy weeds safely on most home lawns. Atrazine products have both pre and postemergence properties and are safe for use on St. Augustinegrass to control many young broadleaf weeds.
Now is the time to treat for cool season weeds with a preemergence herbicide if they have been a problem in the past. Examples of cool season weeds include annual bluegrass, chickweed, thistle, lawn burweed, st1:place w:st="on">Carolina geranium and henbit. When temperatures reach 55 to 60ºF for several consecutive nights and soils are moist, cool season weeds begin to germinate. If the weeds have already germinated, you've missed the window. Don't waste the money or add unnecessary chemicals to the soil. Preemergence herbicides are active for six to twelve weeks after application. Do not use a preemergence herbicide if you plan to overseed with ryegrass or if the lawn is newly planted. Warm season annual weeds (crowfootgrass, sandspur, goosegrass, carpetweed, spurge, chamberbitter, old world diamond-flower, Florida pusley) will begin to die back so treatment now is unnecessary. Wait to treat warm season annual weeds with a preemergence herbicide in late February to early March.
For hard-to-control existing year-round (perennial) weeds, try spot treating weeds with 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. Preemergence herbicides are only effective if the weeds die back and are germinating from seed. To keep crabgrass from germinating from seed next year, apply a preemergence herbicide containing pendimethalin in mid December. 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.
By Terry DelValle, Duval County Environmental Horticulture Agent