by Daniel J. Leonard | May 12, 2022
It’s the most asked question of Extension agents everywhere. “What is this weed and what herbicide should I buy to kill it?” The first part of that question is straightforward. Between personal field experience, formal plant identification training, and a team of weed science specialists to call on, Florida Extension Agents can get your weed accurately identified. The second part of the question is slightly more nuanced. Many weed problems can be avoided by following lawn and landscape Integrated Pest Management (IPM) practices, like not overwatering, mowing at the correct height, using mulch where you can, etc., but sometimes herbicides are required. For these situations, if you follow the “homeowners only need four post-emergent herbicides rule”, you’ll be ready for any weed challenge you face!*
Doveweed seedlings just emerged on July 9, 2021. Photo courtesy of Daniel Leonard.
The first weed scenario you should be prepared for is spot spraying weeds in landscape beds and around hardscapes like concrete pads, sidewalks, pools, driveways, etc. For this situation, you’ll turn to the backbone of the four herbicides rule and a staple in any weed management program, glyphosate. Glyphosate is the active ingredient (AI) in many non-selective products ranging from the infamous Roundup brand to cheaper generics like Killzall and Cornerstone. Glyphostate is extremely cost-efficient and very effective on a huge range of emerged weeds including grassy weeds, broadleaf weeds, and even sedges (also called nutsedge or “nutgrass”). Just be sure not to get any overspray on desirable plants or they’ll be seriously damaged!
The second situation we face occurs when “bad” grassy weeds invade landscape beds, shrubs, and vegetable gardens. These cases call for a grass-selective herbicide that you can spray right over the top of your broadleaf annuals, perennials, and shrubs to take out the unwanted grasses. In this case, there are two options at your disposal: sethoxydim (AI in many products like Fertilome Over the Top, Hi-Yield Grass Killer, Poast, etc.) and fluazifop (AI in the product Fusilade). Both products work well in removing weeds like crabgrass, bermudagrass, goosegrass, and others and can be safely applied over the top of many ornamentals.
Seeds from annuals like Chamberbitter easily get into mulch and turfgrass from surrounding areas. Photo by Beth Bolles, UF Extension Escambia County
From time to time, we need to treat a broadleaf weed like dollarweed, doveweed, chamberbitter, or any number of others, that have invaded our lawn grass. Some of these weeds are tougher than others, but almost all of them can be managed with the proper rates of 2,4-D, Dicamba, other similar products, or a combination of several of them. These active ingredients have been on the market for decades so there are many generic options at your disposal. However, if you have a truly tough broadleaf weed problem, the newer product Celsius WG from Bayer (a combo of Dicamba and two newer AIs), while a little pricey and only available online or at specialty chemical dealers, is well worth the expense and knocks out the most gnarly of lawn weeds.
Finally, there is a category of weeds that aren’t broadleaves and aren’t quite grasses either. These are the sedges. Commonly known around the Panhandle as “nutgrass”, sedges are a serious pest of lawns, particularly those that stay a little on the damp side, and vegetable gardens. Sedges, with their glossy leaves and distinctive flowers, stand out in lawns and gardens, are very unsightly in an otherwise well-maintained area, and can outcompete the desirable plants they invade. Fortunately, there are several AIs that work very well on sedges and are safe to use around turfgrass and many other plants. The most effective sedge herbicide AI for homeowners is halosulfuron-methyl (AI in Sedgehammer in lawns and Sandea and Profine in vegetables). Sedgehammer works very slowly (results can take up to a month) but is very safe in turfgrass and ornamentals and highly effective! If Sedgehammer and other halosulfuron products are difficult to obtain, Imazaquin is a slightly less effective but more common substitute. This AI can be found in the product Image Kills Nutsedge and is safe for use in turfgrass and most ornamental plantings.
The challenge of controlling the many types of weeds in your lawn, landscape, and vegetable garden seems daunting, but having just four basic classes of herbicides on hand can greatly simplify things! Whether you need to control a broadleaf, grass, or sedge weed problem, putting together a weed control toolbox containing a non-selective herbicide like glyphosate, a broadleaf selective like 2-4,D, a grass selective like sethoxydim, and a sedge selective like halosulfuron-methyl can allow you to handle most any weed you come across at home. For more information on controlling weeds in home landscapes and gardens or any other horticultural topic, contact your local UF/IFAS Extension office. Happy gardening!
*Most homeowners discover weed problems after the weeds are already up and growing, making post-emergent products necessary. Pre-emergent products have a place in weed management programs but are not the focus of this article.
by Ray Bodrey | Apr 7, 2022
The thistle has long been an enemy of ranchers, county roadside maintenance crews and homeowners. Often difficult to control, it causes both headaches for producers, in reduction of grazing for livestock as well as being an eyesore for gardening enthusiasts. There are nine different species of thistle in Florida. Most of these are closely related, therefore the control protocols are the same. Only one species is a perennial, and all others are biennial. A biennial plant grows from seed in one year and produces seed for the next.
Thistle that has begun to bolt. Photo Credit: Dr. Jason Ferrell, University of Florida/IFAS Agronomy Department-Weed Science.
It’s important to understand the biology of the thistle in regards of seeking control of this fast spreading weed. This plant will grow a taproot and a cluster of leaves in the first year. This is known as the rosette stage. In the second year, a stalk will appear from the center of the rosette. This is called “bolting”. A seed head will form once the bolting stage is complete. Amazingly, one thistle plant can amass 4,000 seeds. The plant faces its demise after releasing the seeds. The rosette growth stage is mostly during the winter months with bolting occurring from January to July. This is important to note when battling this persistent weed.
As for control, preventing the thistle from producing seed is the most important management measure. Otherwise, little can be done to stop the outbreak of the weed. For homeowners, manually removing the rosette and tap root by hand is effective with small stands. Be careful and wear protective coverings on your hands and arms. Keep in mind, the plant will come back if the tap root is not fully removed.
Other physical control methods, like mowing, have mixed results. This can be effective if mowing occurs after the bolting stage has occurred, but before the seed head forms. However, this is tricky, as thistle plants often do not bloom at the same time.
Thistles in the rosette stage are very susceptible to herbicides. Although, applying a herbicide after the seed head has formed has little effect on control. Herbicides containing 2,4-D are very effective for landscapes. Timing of application is critical. The key to controlling this weed is by scouting and identifying stands as early as possible.
If you’re a beekeeper, there is an upside to this weed. Delicious honey can be made from the thistle bloom.
For more information on thistle, please contact your local county extension office.
Supporting information for this article can be found in the UF/IFAS EDIS Publication, “Thistle Control in Pastures” by Dr. Brent Sellers and Dr. Jason Ferrell.
UF/IFAS Extension is an Equal Opportunity Institution.
by Julie McConnell | Sep 28, 2020
Earlier this summer I talked about getting to know your weeds, so they’ll be easier to control. If you missed that article you can review it here “Why Can’t I Kill Weeds?”
Today we will look at the types of herbicides available so your selection will fit your situation.
Understand your herbicide options. Picking out the appropriate herbicide can be overwhelming. The options seem unlimited when you are standing in the store looking at aisles of containers. By preparing yourself before you shop you can save time and increase your chances of making the most effective selection. Here are some herbicide basics:
- Label interpretation. The pesticide label is a multipage document that describes ingredients, how a pesticide works, application instructions, safety requirements, and other important information for the user. Before applying any pesticide (yes, herbicides are pesticides!) you should read the entire label. Pulling the label off the package in the store may be frowned upon and the print is very small. For this reason, I would recommend looking up a few options before you go shopping and reading the labels online. This allows you to take your time to be sure you understand if it is the appropriate product and you can make your shopping list for personal protective and application equipment before you leave the house. Three important things to look for when selecting your product are active ingredient, labeled site (site includes the location such as residential landscape vs. agricultural crops and the plants it is safe to use on), and targeted pest.
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Non-selective, systemic herbicide damage on grass. Photo: J_McConnell, UF/IFAS
Pre-emergent herbicides. Pre-emergent herbicides provide control when applied BEFORE seed germination of your target weed. They do not prevent germination, rather they prevent emergence of shoots and roots essentially inhibiting normal plant growth which eventually results in plant death. It is important to have your product in place during the correct window of time. Typically, 1-2 weeks before germination of your target weed is ideal.
- For warm season annual weeds (crabgrass, goosegrass, sandspur, and spurge are examples) apply pre-emergent herbicides when day temperatures in early spring reach 65-70°F for 4-5 consecutive days. This may be mid-February or as early as January.
- For winter annual weeds (henbit, black medic, geranium, and chickweed are examples) watch for night temperatures in the Fall to reach 55-60°F for several nights in a row to indicate proper application timing.
- Some products are selective to plant types such as grasses, sedges or broadleaf weeds. Other products are more broad-spectrum and are effective on multiple weed types.
- Pre-emergent herbicide should not be used if you intend to plant seed – it will affect your desired plant in addition to the weed! There may also be effects on newly planted lawns or plants, so be sure to read the label closely to avoid damage to non-target plants.
- Post-emergent herbicides. These products are used on weeds that have already emerged, regardless of life cycle (annual, perennial, biennial). This type of herbicide will be applied directly to the weed you are trying to kill. There are a few categories within this group.
- Selective or non-selective.
Selective herbicides work on particular categories of plants: broadleaf, sedge, grass, or woody plant.
Non-selective herbicides can kill any type of plant regardless of category.
- Contact or systemic.
Contact herbicides kill the plant tissue it comes into contact with and does not translocate to the rest of the plant.
Systemic herbicides are translocated throughout the plant to affect more than just the place of absorption. These are ideal for perennial weeds that would regenerate from roots, bulbs, or tubers if the top is damaged or killed.
Effective weed management requires some preparation and research for the best outcome. For help with weed identification and control recommendations, contact your local UF/IFAS Extension Office.
Further reading on weeds and herbicides:
Florida Homeowner Herbicide Guide: Considerations, Applications, and Selection
Postemergent Herbicides for Use in Ornamentals
Weed Management Guide for Florida Lawns
by Matt Lollar | May 27, 2019
Nobody likes weeds in their garden. Weeds are not only ugly, they can host insects and diseases that later spread to your garden. This situation commonly occurs when weeds belong to the same plant family as the desired landscape or vegetable species, but some insects and diseases have diverse palettes. For example, I recently witnessed a looper caterpillar on a pokeweed plant.
Looper damage on a pokeweed plant. Photo Credit: Matt Lollar, University of Florida/IFAS Extension at Santa Rosa County
Loopers are common pests of vegetable gardens and in the landscape. Probably the most common loopers found in North Florida gardens are cabbage loopers (Trichoplusia ni) and soybean loopers (Chrysodeixis includens). Cabbage loopers can be found feeding on cabbage, of course, as well as leafy greens, cucumbers, tomatoes, chrysanthemums, and snapdragons. Weeds that attract this looper are lambsquarters, dandelions, and curly dock. Soybean loopers like to feed on sweet potatoes, tomatoes, watermelons, geraniums, and sunflowers. They can also be found feeding on oxalis, kutzu, and lantana.
Looper found on pokeweed plant. Photo Credit: Matt Lollar, University of Florida/IFAS Extension at Santa Rosa County
Although weeds can be hosts for pests, they may be used advantageously. Trap crops can be planted at a garden’s perimeter or windward portion to attract pests away from the desired crop. A trap crop draws the pest crop away from the main crop. The trap crop is then destroyed or sprayed with insecticide when the pest insect is found feeding on it. This allows for a reduction or elimination of insecticidal use on the desired crop. However, it is important that both the trap crop and the desired food crop or ornamental crop are regularly scouted to keep track of pest populations.
For more information on trap crops and other insect and disease diversion methods you can read the EDIS Publication: Intercropping, Crop Diversity and Pest Management.
by Matt Lollar | May 17, 2019
Are you looking for more selective herbicide options for annual beds and around shrubs and trees? The Santa Rosa County Extension Office will be hosting guest speaker Dr. Chris Marble from the UF/IFAS Mid-Florida Research & Education Center on Thursday, May 23. Dr. Marble is a Nationally Renowned Weed Scientist who has published numerous research and extension publications. 2 CEUs available in LCLM, Limited Lawn & Ornamental, Commercial L&O, O&T, Natural Areas, ROW, and Private Ag. Pre-registration fee is $15, or $20 registration at the door the day of the event (includes lunch and resources). Pre-register online at Eventbrite Ticket or bring cash, check, or money order to the Santa Rosa County Extension Office, 6263 Dogwood Dr., Milton, FL before May 23. For additional questions, please contact Matt Lollar at mlollar@ufl.edu or 850-623-3868.
SCHEDULE
9:30 Registration & Welcome
9:45 Presentation Begins
11:30 Question & Answer w/Dr. Marble
11:45 Evaluation & CEUs
12:00 Lunch & Discussion on Glyphosate Registration
12:30 Adjourn
