As a boy in a small town in Georgia we had a St. Augustinegrass lawn. My dad started the lawn before I was born. That lawn was still doing fine when I left for college at age seventeen. I don’t remember weeds in the lawn during summer months. I do fondly remember winter “weeds” in that lawn.
To see clumps of winter annuals in our yard and in neighbors’ yards was a natural part of the transition from winter to spring. They added interest to what
Blue Easter egg hidden in chickweed. Photo credit: Larry Williams
would have been a plain palette of green. It was expected to see henbit with its square stiff stems holding up a display of small pinkish purple flowers in late winter and early spring. A clump of henbit was a great place to hide an Easter egg, especially a pink or purple one.
Wild geranium, another common winter annual, offered another good hiding place for Easter eggs with its pink to purple flowers. Large clumps of annual chickweed would nicely hide whole eggs. Green colored eggs would blend with chickweed’s green leaves.
Pink Easter egg hidden in crimson clover & hop clover mix. Photo credit: Larry Williams
Crimson clover with its reddish flowers, hop clover and black medic with their bright yellow flowers were good hiding places for Easter eggs. Plus clovers add nitrogen back to our soils.
I never remember my dad using any weed killer, he rarely watered. The lawn was healthy and thick enough to be a deterrent to summer weeds. But during fall and winter as the lawn would naturally thin and go dormant, winter annual weeds would run their course.
I’ve heard that the sense of smell provides our strongest memories. I remember the first mowing of the season with the clean smell of chlorophyll in the spring air. It was refreshing. Once mowed and as the heat took its toll, by late April or mid-May, these winter annual weeds were gone. What was left was a green lawn to help cool the landscape as the weather warmed. The lawn was mowed high as St. Augustine should be, played on and typically not worried with.
Most people have winter weeds in their lawns that let us know spring is near. Perhaps we worry too much with these seasonal, temporary plants that may have wrongly been labeled as weeds. Besides, how long have we been doing battle with these weeds and they are still here. Most lawns have countless numbers of winter annual seeds awaiting the cooler temperatures and shorter days of early winter to begin yet another generation. By May they are gone.
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.
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
Pesticide labels are not exciting reading materials but they contain necessary details about the specific product. The label information helps you with many decisions to use the product correctly and protect yourself and the environment during the product use. Beth Bolles with UF IFAS Extension in Escambia County will share information about a readily available product and why you should always read through the complete pesticide label.
Why are the plants we are trying not to grow so hard to kill? Weeds can be quite frustrating to home gardeners as they struggle to get them under control. There are a few things you can do to help make your efforts more successful.
Identify the weed. It might seem like it doesn’t matter what the plant is if you know you want to get rid of it, but a big part of your strategy should be figuring out why that plant is being so difficult. Below are the reasons why weed identification is so critical in your fight to control it.
- Which plant are you favoring with your maintenance routine? All plants have similar basic needs: water, sunlight, nutrients, and a space to grow, but some perform better with varying amounts of each of these inputs. Sometimes we can influence these factors in a way that favors one plant over another. The best example is how we irrigate our landscape. If you plant drought tolerant shrubs, such as Indian Hawthorne, which can survive with little to no irrigation after establishment, and then continue to water 2-3 times a week, is it any wonder that you get water loving weeds such as dollarweed, torpedograss, or sedge? Only apply inputs that support your desirable plants and nothing more.
- Recognize the weed type. There are three main types of weeds we typically encounter: broadleaf, grass, or sedge. Some herbicides are broad-spectrum, which means they kill any type of plant, while others are selective. Selective herbicides generally target either broadleaf, grass or sedge weeds and have minimal impact on the other types. This can be very important information to have if you are shopping for an herbicide.
- Understand the life cycle. Herbaceous plants fall into three main life cycle categories: annual, perennial, or biennial. Annuals and biennials tend to reproduce primarily from seed. The annual plant completes its entire life cycle in one season or year and a biennial takes two years. When targeting these two, your goal is to get rid of the plant before it flowers and sets seed to reduce future crops. If you miss that window and the weeds go to seed, plan to use a pre-emergent herbicide prior to their next scheduled germination date (usually the next season). Perennials live for more than 2 years and tend to be tough to manage. They may reproduce by seed but many also multiply by vegetative means. To put this simply, they store everything they need in tiny pieces of the plant and if left in place, it will generate more plants. So, that little tiny root fragment from dollar weed you didn’t pull up – yep, it’ll grow a whole new one in its place!
For more information on weeds and weed control in lawns and landscapes, contact your local UF/IFAS County Extension Office!
This time of year, owners of woody plants might notice that leaf canopies are thin. Fruit and ornamental trees, shrubs, and bushes might have shed some leaves over the winter or thinned out due to disease, cold damage, or other problems. When this happens, it can call more attention to the stems of these plants, which may sport a fuzzy, frilly growth on them. More than once I’ve heard people ask, “What is this growing on my plant and how do I stop it from killing it?”.
Red Tipped Lichen – Image Credit Evan Anderson UF / IFAS Extension
Lichen is the fuzzy growth in question, and the good news is that it doesn’t harm the plant it grows on. Lichen is an organism that’s a combination of fungus and either algae or cyanobacteria. The algae photosynthesizes and produces energy to share with the fungus, which provides protection and support. Thankfully, they’re pretty self-contained, and don’t need to steal nutrients or water from whatever they’re growing on. That means they can grow just about anywhere – on rocks, fence posts, tree bark, or on the ground (if you’ve seen deer moss growing in the woods, that’s a lichen!). Again, they are NOT parasitic and do NOT hurt plants.
Lichen on Tree Trunk. Image Credit Evan Anderson, UF / IFAS Extension
It’s common to find lichens growing in many different forms and colors. One alarmed tree-owner brought me a branch decorated with a round blotch that had a bright reddish edge. A Christmas Wreath lichen had found a home on her tree, and while the red rings it forms may look alarming, they’re just as innocuous as other lichens. There may be multiple forms of lichen growing in close proximity on a branch, as well. Flat, wavy, rippled, filamentous, bushy, and powdery looking lichen might all mix together to make a strange (or beautiful) looking collection on a tree.
Most lawn weeds are annoying, appearing in unwanted places and numbers, but few actually cause physical harm like the pest plant Lawn Burweed (Soliva sessilis)! This infamous small, spreading winter weed’s seeds generally germinate when temperatures begin to cool in the fall (late October-November). Burweed then grows mostly unnoticed through the winter until spring, when it then produces the hard, spiny burs that contain the plant’s seeds and the plants finally die. Once the burs have formed, Burweed’s presence makes walking on newly greened-up spring turf extremely painful for pets and people (barefoot of course, the burs aren’t large enough to puncture shoe soles). At this point of the plant’s life, once it has made its unwanted presence known, control is not feasible as the Burweed plants have set seed, ensuring a new crop next year, and killing the remaining foliage doesn’t remove the burs. What is a homeowner to do?
Newly germinated Lawn Burweed. Photo courtesy of the author.
Fortunately, Lawn Burweed is relatively easy to control chemically if one pays close attention to seasonal changes and uses herbicides (either pre-emergent or post-emergent herbicides) effectively.
Pre-emergent Herbicide Options: The first chemical control option for Lawn Burweed is a timely application of the pre-emergent herbicide Isoxaben (sold under various brand names at most farm or garden stores) to prevent Burweed seeds from germinating, greatly reducing plant populations. However, pre-emergent Isoxaben applications must be made before the plants sprout and begin to grow to be effective. For Burweed, this generally means application in October, once nighttime temperatures dip into the 55-60 degrees F range for several nights in a row, as consistent temperatures in this range give Burweed seeds the signal to germinate. Though we’re already past the point of pre-emergent herbicides being an option for control this year, homeowners should plan to include this method in their Lawn Burweed control plan for fall 2020!
Post-Emergent Herbicide Options: If you haven’t already used a pre-emergent herbicide this fall for Burweed control, you must turn to post-emergent options. Like pre-emergent herbicides, timing is critical if you want your post-emergent applications to work! These herbicides are most effective when Burweed plants are young, small, vigorously growing, and haven’t set burs yet. Successful post-emergent applications may be made from December-early February before burs harden. Unlike pre-emergents, where there is only one strong option for Burweed control, many post-emergent herbicides exist that are extremely effective! When shopping, look for products containing the following active ingredients:
Lawn Burweed around 10 days after emergence. Photo courtesy of author.
- Atrazine – sold under many brand names and safe in Centipede, St. Augustine, & Bermudagrass. Do not use in Zoysia or Bahiagrass lawns.
- Dicamba, Mecoprop, 2,4-D – commonly sold in three-way formulations through many brand names. Generally safe in Centipede, St. Augustine, Bermuda, Zoysia, & Bahiagrass lawns.
- Metsulfuron – sold under several brand names and safe in Centipede, St. Augustine, Zoysia & Bermudagrass. Do not use in Bahiagrass. Be careful if used around ornamentals.
- Thiencarbazone, iodosulfuron, dicamba – sold as Celsius WG from Bayer. Safe in Centipedegrass, Zoysiagrass, Bermudagrass, and St. Augustinegrass. Do not use in Bahiagrass.
Lawn Burweed control with of all the above-listed herbicides will be most effective with a follow-up application 10-14 days later.
Note: With the exception of the Thiencarbazone, iodosulfuron & dicamba mixture (Celsius), do not apply any of these post-emergent herbicides during spring turf green up.
As always, if you have questions about Lawn Burweed control or any other horticulture or agriculture related questions, please contact your local UF/IFAS County Extension office or consult any of the following related articles: https://nwdistrict.ifas.ufl.edu/hort/2015/10/06/lawn-burweed-prevention-is-easier-than-cure/ and http://blogs.ifas.ufl.edu/washingtonco/2017/10/11/prepare-now-to-avoid-lawn-burweed-infestation-later/