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!
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.
For a state that receives around 60” of rainfall a year, it is sure dry in Florida right now! In the Panhandle, the majority of our annual rainfall occurs in in bunches during winter and early spring via near-weekly cold fronts, in the mid-summer as a result of afternoon thunderstorms, and periodically in late summer/early fall if a tropical system crosses our path. Mixed in, however, are two distinct, historically dry periods: the first one in April through mid-May (contrary to popular myth, if we have May flowers, they’re gonna have to make it without April showers) and the second right now in September and October. The prolonged second dry period that we’re experiencing now makes it difficult to manage the mostly unirrigated, low-input turfgrass common in rural Panhandle lawns and pastures. It is critical to enter these expected droughts with healthy turf and remembering to employ 3 simple management tips when it quits raining (although you should follow them year-round ideally) can greatly increase your turf’s resiliency!
Unirrigated Centipdedegrass turf showing drought stress- Photo courtesy of the author.
Water Wisely – The average Florida turfgrass requires ¾-1” of water per week and we generally achieve that through rainfall. However, in our droughty months, supplemental irrigation can be a lawn saver, particularly in high traffic or more stressed areas of the yard. I realize that many of you, myself included, maintain large lawns without irrigation systems and it’s impossible to keep all your lawn well-watered during drought, but you can maintain the areas around your home, hardscapes and landscaped beds with the highest impact/visibility nicely! In these areas, put down no more than ¾” of water per irrigation event, a ballpark number that ordinarily allows the turf root zone to become saturated. Measuring your sprinkler’s water output is easily done by setting several straight-sided cans (tuna or cat food containers work great) under the sprinkler and timing how long it takes to achieve 3/4”. You might be surprised how much water you waste by leaving a sprinkler running for an hour or more!
Apply Herbicides Appropriately – Herbicides are a great item to have in the turf care toolbox, but if used incorrectly can be a waste of time and money at best, harmful to your turf at worst! Once turf and associated weeds become drought stressed (turning bluish gray, obvious wilting, leaves curling, etc.), it is too late for weed control with herbicides. There are a couple of reasons for this. First, when plants get stressed, they slow or stop their growth and focus on survival. This survival response prevents herbicides from being taken up properly and ultimately causes ineffectual weed control. Also, many herbicides specifically state on the product label that they should not be applied during certain conditions (drought, temperatures above 85-90 degrees, etc.). It is critical that one adhere to these label directions as applying the incorrect product in hot and dry conditions can cause volatility, drift to non-target plants, and in some cases, toxicity to turf you’re treating in. When it’s droughty like it is now, leave the herbicides in the chemical shed to prevent wasting your time and money and potentially damaging non-target plants!
Unirrigated Centipedegrass turf showing drought stress – photo courtesy of the author
Raise that Deck – Finally, one of the most important turf management strategies during an extended drought is to reduce mowing and raise your mower’s cutting height when/if you do mow. As mentioned above, plants are already stressed during a drought and physically chopping off a chunk of the turf plant stresses it further, causing an energy-intensive wound response when the plant is actively conserving resources for survival. Therefore, if you just HAVE to mow, raise the cutting height as high as possible to make the smallest injury possible on the grass and keep your mower blades sharp to ensure a clean cut, which will heal easier and require a smaller energy response from the plant.
During droughts like the one we’re currently in, there isn’t one silver bullet to keep your non-irrigated turf looking good. However, there are several strategies you can use throughout the year to get your lawn through dry times. Remember to water ¾”-1” per week when you can, where you can. Before you water, calibrate your sprinkler to ensure you put out enough water and don’t waste your time and inflate your utility bill by putting out too much! Reduce or eliminate use of herbicides as they are ineffective during stress periods and can harm your turfgrass. Finally, reduce or eliminate mowing and if you must mow, raise the deck! If you have any questions about getting your turf through the drought or other horticultural or agronomic topics, please contact your local UF/IFAS Extension Office!
Weeds identification and management is still one of the most common questions we receive at the local UF IFAS Extension office. Learn about the chamberbitter weed that can grow in turf and ornamental beds and the multi faceted approach that is necessary for management In the Garden with Beth Bolles, UF IFAS Extension Escambia County.
