Pre-emergent fertilizers are a type of fertilizer that is applied to the soil before the seeds have germinated. This helps to control weed growth and can be an effective way to keep your garden looking neat and tidy. There are many different types of pre-emergent fertilizers on the market, so it is important to do your research before selecting one and incorporating it into your lawn care practices.
6 most common Pre-Emergent Herbicides
Benefin
Short for Benfluralin, benefin is the active chemical ingredient in pre-emergents that work particularly well on controlling grasses and broadleaf weeds on turfgrasses. Benefin is a dinitroaniline, meaning that it works by inhibiting mitosis in seedlings that then prevents cell division. With a lack of cell division, the seedling will not be able to develop mature roots and sprout out of the soil.
While Benefin is non-toxic to humans, birds and mammals, it is toxic to fish so avoid the use of this pre-emergent if you live by a body of water.
This pre-emergent usually comes in a liquid form but does have the option of coming in granular form. When in granular form it is often combined with Trifluralin to be used on turf grass. If you choose to use the granular form, be sure to water the pre-emergent after you have applied it to your lawn. Benefin takes on average about 5 to 6 hours to be fully absorbed into the soil. From there, it will begin inhibiting seed growth.
Benefin is a great pre-emergent choice when trying to control broadleaf weed and grasses. Here are the most common weeds and grasses this pre-emergent is used on:
- Bluegrass
- Chickweed
- Crabgrass
- Carpetweed
- Knotweed
- Purslane
- Red Clover
- Rye Grass
- Seeded Alfalfa
- Seeded Lettuce
Dithiopyr
Dithiopyr is the active chemical ingredient in pre-emergents that was best on grassy weeds such as crabgrass and oriental grass, and it can even double as an early post-emergent on some weed species, including crabgrass, if you apply it to the weed before it tillers. It is the perfect choice for use around ornamental turf and plants, established lawns, industrial and non-cropland sites, and commercial sod farms.
The only cons with this pre-emergent is that it does not work great on broadleaf weeds and all though it has low toxicity levels for humans, birds and mammals, it is toxic to fish, so if you live by an open body of water or runoff areas, it is advised to select a different pre-emergent for your property.
Dithiopyr works by inhibiting mitosis in a seedling’s roots, this causes the seedling to inhibit spindle production, preventing the plant from sprouting and maturing. It is available in multiple forms including powder, granules and liquid concentrate for spraying. If you choose to use the powder or granular form, be sure to add water to the product after applying it to your lawn or garden so that it can be absorbed into the soil beneath it.
Dithiopyr is best for controlling the growth of different grasses. Here are some of the plants that pre-emergents containing dithiopyr work well on:
- Barley
- Bittercress
- Bluegrass
- Chickweed
- Crabgrass
- Dandelion
- Goosegrass
- Foxtail
- Rye Grass
- Willow Herb
- Wood Sorrel
Isoxaben
Isoxaben is the active chemical ingredient in pre-emergents that work best for selectively killing broadleaf weeds and it can be used as a pre-emergent herbicide for vines and grasses as well. Isoxaben is safe to use around trees and ornamental plants, as well as turf grass.
This pre-emergent is moderately toxic to humans and can cause chronic harm to small mammals, birds and fish so be sure to follow the instructions and use caution when applying to your property.
Isoxaben works by inhibiting the production of enzymes needed for protein synthesis within a seedling. This ultimately kills the seed before it has any chance to germinate and sprout from the ground. This pre-emergent can be found in powder, granular and liquid concentrate forms. If you choose to use the powder or granular forms be sure to water after applying to your lawn or graden. When selecting liquid concentrate form, be sure to read the labels because isoxaben concentrations in popular herbicides currently found on the market come in a range from 0.25% to 75%. The higher the concentration, the longer-lasting the pre-emergent effects will hold. In general Isoxaben can work up to 8 months with just a single application.
This pre-emergent is effective on nearly 100 different species of broadleaf weeds and grasses. Here are just a few of those weeds:
- Aster
- Bursage
- Burweed
- Chickweed
- Clover
- Henbit
- Horseweed
- Knotweed
- Pigweed
- Purslane
- Ragweed
- Sibara
- Smartweed
- Sowthistle
- Speedwell
Pendimethalin
Pendimethalin is the active chemical ingredient in pre-emergents that are one of the most effective for controlling broadleaf weeds and grasses in food crop areas. It is primarily used to target weeds that can pose a threat to agricultural areas such as, soybean, corn, tobacco, potato and cotton fields.
Some cons are that this pre-emergent can stain hard surfaces such as driveways and sidewalks, it cannot reseed until 4 months after use and, although non-toxic to birds, it is slightly toxic to humans and mammals, and is highly toxic to fish. So when handling pendimethalin, be sure to read all instructions carefully, avoiding the application of this pre-emergent if you live near a body of water or any run-off areas. Also, make sure to wear proper safety gear to protect yourself from any dangerous side effects.
Pendimethalin is a selective pre-emergent that halts mitosis and inhibits cell growth, preventing target weed seedlings from developing mature roots. It can be found in both liquid and granule forms and it can be used to treat a wide range of broadleaf weeds and grasses.
Prodiamine
Prodiamine is the active chemical ingredient in pre-emergents that work best on turfgrasses and around ornamental shrubs and trees. It is the most popular and most effective pre-emergent weed killer on this list. It controls broadleaf weeds and invasive grasses such as crabgrass. It is safe to use on all turfgrass such as Fescue, St. Augustine, Bermuda and more.
The only real con to this pre-emergent is that it has a high run-off risk in the event of rain, so keep this in mind if you live near a body of water.
Prodiamine works by blocking cell division that prevents root growth. Using this as a pre-emergent over the winter months will give you the best results. This pre-emergent is available as a water-soluble granule or liquid concentrate, controlling invasive grasses and broadleaf weeds.
Here are some of the grassy and broadleaf weeds prodiamine is effect against:
- Chickweed
- Bluegrass
- Clover
- Crabgrass
- Creeping Bentgrass
- Dandelion
- Goosegrass
- Purslane
- Spurge
- Thistle
- Witchgrass
Trifluralin
Trifluralin is the active chemical ingredient in selective pre-emergent herbicides that work best on broadleaf weeds and annual grasses in flower beds and amongst vegetable crops. It controls weeds and grasses that can be found in various flower and crop groups such as broccoli, cabbage, beets, sugar cane, and other crops that are used as animal feed.
While trifluralin is non-toxic to birds, it is proven to be highly-toxic to fish and has even been classified by the EPA as a Class C possible human carcinogen. Don’t be too alarmed, for the likelihood of the chemical transmitting into crops is very low.
This pre-emergent works by fully stopping mitosis and cell division in the roots of different weeds and annual grasses. This prevents the seeds from ever emerging from the soil. It is available in both liquid concentration and granule forms, however is found to work best as a liquid concentrate.
Here are some Broadleaf weeds and annual grasses trifluralin is effect at killing:
- Annual Bluegrass
- Barnyardgrass
- Crabgrass
- Johnson Grass
- Chickweed
- Goosegrass
- Sandbur
- Purslane
- Thistle
How to select a pre-emergent fertilizer
When selecting a pre-emergent fertilizer, it is important to consider the specific needs of your garden. Some fertilizers are designed for vegetables, while others are meant for flowers or trees. It is also important to choose a fertilizer that will be effective against the weeds you are trying to control. and the guide above will be an excellent resource in helping you pick the best solution.
Once you have narrowed down your options, it is important to read the label carefully to make sure the fertilizer does not contain any harmful chemicals. Always follow the dosage instructions on the label, and never apply more than recommended.
When to apply pre-emergent fertilizers
Timing the application of your pre-emergent is just as crucial as selecting the right herbicide for your problem weeds.
Different pre-emergent fertilizers work in different ways. Most of the ones I have listed here today only work once the seedlings have sprouted and before they emerge from the soil above. If applied too early, the herbicide can drain from the surrounding soil, missing its opportunity to kill the weed, leaving you with an ever growing problem.
The time of year you apply will also vary depending on the type of fertilizer you are using. For example, prodiamine is most effective when used over the winter months. Whereas most others should be applied when outside temperatures reach and maintain around 55 degrees Fahrenheit to be most effective.
Be sure to follow the dosage instructions on the label, and never apply more than recommended.
Final Thoughts on Pre-Emergents
Pre-emergent herbicides are an important part of any gardeners toolkit. They provide an easy and effective way to control weed growth, and can help keep your garden looking neat and tidy. There are many different types of pre-emergent herbicides on the market, so it is important to do your research before selecting one. We have provided a guide to some of the most common types, as well as a list of broadleaf weeds and annual grasses they kill. It is also important to time the application correctly for best results. Be sure to read the label carefully and follow the dosage instructions and if you feel your weed problem is too large to solve yourself, then contact your local lawn care company to get the best advice.
