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.
Florida pusley and its relatives, Brazilian and large-flower pusley, are common sights in lawns and landscapes during the summer. These prolific and tenacious weeds are closely related species in the genus Richardia, in the Rubiaceae family which includes coffee, bedstraw, and the plant from which the emetic ipecac is derived. With their thick leaves, low and spreading growing habit, and bright white flowers, they can quickly take over bare spots in a lawn and become quite a nuisance.
Because bare spots are a magnet for pusley (and weeds in general), one method to help prevent this weed from becoming a problem is to ensure the turfgrass is as healthy as possible. Well established grass can outcompete many other competitors. Keeping a lawn in tip-top shape includes watering properly, mowing at the recommended height for the grass species and variety, fertilizing appropriately, and controlling pests and diseases in a timely fashion. This can take some work in North Florida’s hot, humid climate, but prevention is almost always easier than trying to cure a problem.
Florida pusley is quickly noticed as soon as it flowers. While some may find the flowers attractive, they set seeds swiftly and before you know it, the next generation of plants is ready to go. Surprisingly, they are also an important nectar plant for honeybees. If chemical control is warranted for an infestation, a pre-emergent herbicide may help. Timing is important for this, so keep an eye on the thermometer – pre-emergents should be applied in the spring (February or March) when temperatures reach 65-70 degrees Fahrenheit for four to five days in a row. Examples are products with active ingredients such as atrazine or pendimethalin, though atrazine should not be used on bermudagrass or bahiagrass.
For weed problems that are already established, there are post-emergent herbicides available. In bahia, bermuda, and zoysia, products containing 2,4-D (or mixtures, such as 2,4-D and dicamba) can work fairly well. These products may require two applications to adequately control pusley. Be aware that some herbicides are sold under trade names that may be confusing, such as Roundup for Southern Lawns, which is a mixture of 2,4-D and penoxsulam, and is labeled for use on bahia, bermuda, St. Augustine, and zoysia grasses . It does not contain glyphosate, and Roundup that DOES contain glyphosate will kill turfgrass as well as weeds. Check the active ingredients on the herbicide label.
In St. Augustine lawns, options are more limited. Homeowners with St. Augustine may want to consider contacting a lawn care company for help with pusley. The available herbicides that are labeled for use in this instance are either difficult to use or prohibitively expensive (The herbicide Celsius, for example, costs over $100 per 10 oz. bottle). Another chemical that is effective is metsulfuron, and while it can be used in bermuda and zoysia lawns as well, it comes with some serious difficulties. First and foremost, it can be taken up by the roots of plants and is NOT safe to use around trees or shrubs. Properly measuring the chemical is tricky, as it may take only a single ounce to treat a whole acre. Serious damage can be done to surrounding plants if it is mixed or used improperly, and as such it may be difficult to find at local stores.
Homeowners who choose an herbicide to control pusley or any weed should be aware that high temperatures during the Florida summer can cause chemicals to affect the grass as well. St. Augustine is especially prone to this, and some herbicides such as 2,4-D may affect grasses more when temperatures rise above 85-90 degrees Fahrenheit.
A closeup of Florida pusley flowers.
Treatment of pusley and weeds in general is most effective when the plants are young. Large pusley plants have deeper roots and may take more applications of herbicides to control effectively. Furthermore, of the pusley species that can be found in our area, large-flower pusley is more difficult to control and may be tolerant of some chemicals. For more information, contact your local Extension office.
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.
North Florida vegetable gardeners have made it to summer and now the plants and gardeners are starting to give in to the heat and humidity. The squash has likely succumbed to squash vine borers, many of the tomato varieties are having trouble setting fruit, stink bugs are all over, and gardeners easily wilt by noon. This is a good time to use our oppressive heat to your advantage in the vegetable garden by solarizing the soil.
We have reached the peak of heat. Use it to your advantage in the garden. Source: National Weather Service.
Soil solarization is a method of pest control that creates a greenhouse to heat up the soil in an effort to drive away pests. Pests that can be reduced with soil solarization include weeds, various soil-borne fungal pathogens, and nematodes. Weed seeds can actually be killed by the increased temperatures, sometimes as high as 140 degrees Fahrenheit, while fungi and nematodes are merely driven deeper into the soil layer as they try to escape the heat. Although they are not killed, this can help vegetable gardeners as it may take these organisms 3-4 months to repopulate in high enough numbers to cause damage. Soil solarization can be considered another tool in your integrated pest management (IPM) toolbox, along with other cultural, physical, and chemical means of pest control.
A raised bed being solarized over the summer. Source: Evelyn Gonzalez, UF/IFAS Master Gardener Volunteer.
To properly execute soil solarization, the site should be in full sun and the existing vegetation removed, either by hand or with a tiller or other implement. Tilling can help loosen the soil surface and allow heat to penetrate deeper in the soil horizon. Before being covered with plastic, the area should receive rainfall or be irrigated, as the water will help conduct heat to greater depths. The next step is to cover the area with plastic. Note that this can also be done over raised beds! Clear plastic is best for maximum solar radiation penetration. Black plastic will heat up mostly on the surface and opaque plastic sheeting may not let enough light in to get temperatures high enough. The plastic should be slightly larger than the area covered, as the edges will need to be buried to create an air-tight seal. It’s recommended to leave the plastic in place for at least six to eight weeks, just in time to begin fall gardening preparations.
It’s important to monitor the site while it’s “cooking” to look for any holes that might appear. Small holes can be repaired with duct tape, while large holes or rips in the plastic may require starting over. Overlapping strips of plastic is not recommended since too much heat will be lost.
You may be wondering what happens to all of the good soil microbes. Well, unfortunately, they are also either killed or suppressed. Fortunately, researchers have found that they are able to repopulate quicker than the pest organisms, especially in soils with a good amount of organic matter.
Much more information on soil solarization can be found in these two documents:
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!
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?”
