By Jane Morse, University of Florida/IFAS Extension Agent, Pinellas County Extension
Weeds in Florida can be a nightmare. Abundant summer rains and scorching sunshine lead to lots of germinating (sprouting) weed seeds. Weed control in the fall isn’t too bad, but trying to keep up with weeds in the blistering heat of summer, while dodging rain storms, sweating, and swatting mosquitoes is miserable.
To control weeds we need to have a basic understanding of some of their differences and how we can use these differences to our advantage.
First, let’s learn about the types of weeds. There are broadleaf weeds. These types of plants generally have net-like veins in their leaves and many have showy flowers. Some examples are dollarweed, creeping beggarweed and Florida pusley. Grass weeds have hollow, rounded stems and nodes (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 “grass-like” weeds, but they 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.
Plants are also distinguished by how long they live. Some are annual (they germinate, grow, flower, seed and die in one year). Others are biennial (it takes two years to complete their life cycle). The hardest to control plants are perennial (they live more than 2 years) because they have several means of reproducing. Not only may they reproduce by seed, but they may reproduce vegetatively by bulbs, rhizomes, stolons, or tubers.
There are two basic methods of weed control -- physical control and chemical control. Usually the best control is achieved using a combination of these two methods.
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 1/3 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 flowerbeds, footpaths and other areas where there is no grass. Mulch works by smothering out weeds by excluding light. Mulch should be applied about 2 inches thick and kept away from the bases of plants.
Chemical weed control is the use of herbicides. There are different types of herbicides. Selective herbicides control certain plant types without seriously harming other plant types. A selective herbicide might kill broadleaf plants while not seriously harming grass plants, or vice versa. Non-selective herbicides kill most plants regardless of type. Roundup® (Glyphosate) is probably the most widely known and used non-selective herbicide. Then there are pre-emergent herbicides that prevent seedlings from growing and post-emergent herbicides that are applied to existing weeds when they are small and actively growing.
Selective herbicides can be very useful if, for example, you are trying to control grass weeds in a broadleaf planting, or trying to control broadleaf weeds in a grass planting. Grass-B-Gon® (Fluazifop) is a selective herbicide that kills unwanted grasses in and around broadleaf ornamentals. Manage® (Halosulfuron-methyl) is a selective herbicide for controlling nutsedge in turfgrass and landscaped areas.
Non-selective herbicides are most commonly used for killing plants in a large area. For example, if you were replacing a turfgrass area and wanted to clear the area of all plants a non-selective herbicide would be a good choice.
Pre-emergent herbicides offer very good weed control because they keep the weeds from sprouting and growing. Some weeds like crabgrass can only be effectively controlled with a pre-emergent herbicide. Pre-M® (pendimethalin) is a pre-emergent that controls some annual grasses (crabgrass, etc.) and certain broadleaf weeds. It can be used on St. Augustine or Bahia grass and on many ornamentals for weed control. The most important thing about pre-emergent herbicides is timing. They must be applied before the weed seed germinates. Therefore it is important to know the identification of the weed you want to kill and when it germinates.
Post-emergent herbicides are applied to already existing weeds. They work best on young, rapidly growing plants. Some herbicides control some weeds better than others. Again, it is important to correctly identify the plant you want to kill so the best herbicide can be selected to obtain effective control.
Whenever chemicals are used it is extremely important and crucial to read the label and follow the directions exactly. Not following the label directions can be harmful to the environment and people, and is against the law.
For more information or help selecting herbicides contact your local University of Florida Extension Service in Pinellas County at 727-582-2100. Visit our website at: http://pinellascountyextension.org or come to our office at 12520 Ulmerton Road, Largo, FL. Office hours are M-F from 8AM to 5 PM.
Note: Use of brand or trade names in this publication does not imply endorsement of the products or criticism of similar ones not mentioned. Trade names are used herein for convenience only. Mention of a proprietary product does not constitute a guarantee or warranty of the product by the author.
Information for this article came from these publications: http://edis.ifas.ufl.edu/WG071 ; http://edis.ifas.ufl.edu/EP141 and http://edis.ifas.ufl.edu/document_wg058