From April SportsTurf “Q&A with Pamela Sherratt: Q: We are getting ready to overseed our soccer field this spring. What weed control options are there? A: Successfully growing cool-season turf from seed in the spring can be a challenge because the weed pressure is so great, which is one if the reasons why the recommended Learn how to kill weed seeds in soil to prevent weeds and other invasive grasses from continuing to sprout every year. Harvest Weed Seed Control At harvest time, weeds that have escaped season long management often have mature seed still attached to the parent plants. These weed seeds can enter the combine along
Weed control during spring seeding
From April SportsTurf “Q&A with Pamela Sherratt:
Q: We are getting ready to overseed our soccer field this spring. What weed control options are there?
A: Successfully growing cool-season turf from seed in the spring can be a challenge because the weed pressure is so great, which is one if the reasons why the recommended time to do renovation is in the fall. In the real world however, athletic fields are in a constant state of renovation and so seeding is a season-long operation.
Weeds that emerge in spring, like crabgrass, prostrate knotweed, yellow nutsedge, goosegrass and annual bluegrass are particularly troublesome on athletic fields because they can germinate and establish quickly, even on compacted soils. Weed seed present in the soil is laying dormant just waiting for an opportunity under the right environmental and cultural conditions to invade a weakened turf with bare soil. Because weed pressure is so great in the spring and early summer months, it is important that the soil is not disturbed (avoid tilling as this will bring up weed seeds) and that the seedbed be treated with an herbicide that does not adversely affect germination of the desired grass seed.
There are several approaches to using an herbicide during the seed establishment period. Following is a summary of those options, based on years of herbicide trial work by Dr. Dave Gardner. One strategy is to seed in early spring and then after the seedling turf has established, apply an herbicide with pre and early postemergence activity, such as dithiopyr (Dimension, others*). This strategy requires very careful timing, and on most athletic surfaces, overseeding is not a once per year operation. Once the application of dithiopyr is made, as is the case with most preemergence herbicides, future overseeding operations must be delayed according to the label.
In fact, on areas that you plan on seeding or over-seeding in late spring or summer, hopefully you did not apply a preemergence herbicide. If you did, then be aware that almost all of the preemergence herbicides on the market are very effective at controlling not only weed seedlings, but also the seedlings of our desired turfgrasses. Fortunately, there are three preemergence herbicides that are labeled for use at seeding time: siduron (Tupersan), mesotrione (Tenacity), and topramazone (Pylex).
Siduron has been available for use in turf for many years. It is safe for use on seedling turf. Follow the label directions carefully. When used properly, siduron will reduce crabgrass, goosegrass, foxtail, and many summer annual broadleaf weeds by about 80%.
Mesotrione is in a unique class of chemistry and this product has a very diverse label, including pre- and postemergence control of both broadleaf weeds and annual grasses. It also controls sedges preemergence and certain perennial weedy grasses postemergence. One of its key uses is the preemergence control of annual grassy and broadleaf weeds in newly seeded turfgrass. When used as directed, mesotrione will result in nearly complete control of crabgrass, goosegrass, foxtail, and many summer annual broadleaf weeds. But, it will not affect the growth and development of the seedling turf. Most effective use of this product is to apply it to the soil surface right after the seeds have been raked in but before mulch is applied.
You can then begin to irrigate as you normally would to establish seedling turfgrass. Mesotrione is very safe to seedling turf. However, some phytotoxicity has been reported if it is applied to young turfgrass seedlings. If you are using multiple applications of mesotrione as part of a program to control stubborn weeds, such as creeping bentgrass, then you want to avoid overseeding or reseeding the area until you are making your last mesotrione application. In other words, it is better to wait and reseed with the second or third mesotrione application, then to seed when the first round of mesotrione is being applied.
Topramazone is a more recent introduction to the turfgrass market. It is similar to mesotrione in its weed control spectrum and its safety to seedling turfgrass. Make sure to follow the label recommendations carefully.
After the seed has germinated there is a period of time in which your options for weed control become limited. Most postemergence herbicides for broadleaf weed control have language on the label that states that following seeding, the turf needs to be sufficiently established so that it has been mowed three times before the product can be safely used.
All of the herbicides mentioned in this column are good products and can be quite effective. You can help to improve your chances of success by avoiding the 2-4 week period each year that is the peak of germination for the particular weed species that dominate your fields. For example, each of these products is quite effective at reducing weed establishment when seeding or over-seeding in July when weed competition begins to drop off. However, each of these products can produce less than complete weed control if used in mid to late May. This is more likely to be a problem if the May timing is in conjunction with seeding a slower to germinate species such as Kentucky bluegrass. By simply waiting a couple of weeks (or seeding a couple of weeks earlier), weed seed competition may be greatly reduced, which further increases your chances of success when seeding or overseeding.
*Mention of a specific product does not constitute an endorsement over other products that may be similar
How to Kill Weed Seeds in Soil [5 Easy Methods]
To kill weed seeds in soil you will have to apply one or more of the following methods:
- Heat soil to temperatures high enough to kill weeds seeds
- Force seeds to sprout and destroy growing weeds
- Apply chemical or natural weed killers that prevent weeds from sprouting
- Use flame weeding to destroy weeds and seeds at once
- Layer mulch in garden areas to suppress weed sprouting and attract insects that eat seeds
With this arsenal of tricks for killing weed seeds before they sprout, you can stop the spread of weeds in both your lawn and garden.
Table of Contents
5 Tips for Killing Weed Seeds
Rather than spending time and effort battling weeds as they sprout, attack weeds at the source by killing weed seeds. Each of these methods destroys weed seeds, which ensures you won’t have to battle recurring weed invasions. Try these ways to get rid of weed seeds yourself.
Soil solarization is a very powerful method for killing weed seeds. Weed seeds begin to die if soil temperatures surpass 108 degrees, with full seed death ensured by soil surface temperatures of 140 degrees or more. Solarization uses clear plastic tarps to trap heat at the soil surface, killing weed seeds within the tarped area. To solarize an area, follow these steps:
- Clear the area of all vegetation through use of a hoe or other garden implement. Remove any woody stumps
- Till the soil to further break up any weed root systems left behind.
- Rake away all vegetation residue
- Water the tilled and cleared soil with a garden hose until it is damp.
- Lay a sheet of clear plastic over the area. Weigh it down tightly at the edges
- Leave the plastic in place for at least two months.
Solarization is the best method to reclaim a weedy garden or other area. It is a “clean slate” for your soil, because seeds will be destroyed by the solar heat trapped beneath the plastic.
It is typically tough to implement solarization in large areas and is not usually suitable for use in lawns, where you may want to preserve grass or other plants. Pre-emergent weed killers and flame weeding are much better for use in lawns.
Till and Kill
Weed seeds can lie dormant in soil for decades and are only “activated” when brought to within an inch of the surface. One method to rid soil of dormant weed seeds is to force these dormant seeds to sprout, then attack them with a powerful natural or chemical weed killer. To do this:
- In spring, till the affected area. Tilling brings dormant seeds to the surface
- Water the area for 1–2 weeks with a sprinkler or soaker hose
- When weeds begin to sprout, apply the weed killer of your choice
This is another “clean slate” method, where you force weed seeds to show themselves and then kill young weeds before they mature and cast seeds. Because of the invasive tilling step, it is not best used in areas with desirable grasses and plants.
Use Pre-Emergent Weed Killer
Pre-emergent weed killer stops weeds in their tracks. It works by attacking weed seeds just as they begin to germinate, killing them before they even poke above the surface. It’s a weed killer so good, the only sign it’s working is that there will be no new weeds at all.
Harvest Weed Seed Control
At harvest time, weeds that have escaped season long management often have mature seed still attached to the parent plants. These weed seeds can enter the combine along with the cash crop, exit the back of the combine as chaff (small plant pieces and weed seeds), and be spread across the field, as well as from one field to another. It seems a waste to spend all year spraying weeds with expensive herbicides only to reward the survivors at harvest by spreading their weed seeds out for next year.
An excellent way to stop weeds in their tracks is to collect these weed seeds at harvest and either destroy them or deposit them in a known location where they can be monitored and controlled later. Soybean, wheat, and other crops harvested with a grain header are ideal choices for harvest weed seed control (HWSC). Other crops such as cotton and corn need further equipment development to make HWSC a viable option.
If you are considering adding harvest weed seed control (HWSC) to your weed control program there are excellent resources on the WeedSmart website to help guide you through the initial decisions and the implementation of this important weed control tool.
3 steps to get it working for you
1. Decide which system fits your farm best.
2. Get maximum weed seed into the header.
3. Know how to manage the collected weed seed.
What is Harvest Weed Seed Control?
Choose The Best System For You
Which system is best?
HWSC is being rapidly adopted in Australia and other countries around the world. There are six systems currently being used on Australian farms and they have been initially developed by farmers.
Research has demonstrated that all are very effective weed seedbank management tactics for a range of weed species, achieving over 80 percent control and for some nearly 100 percent.
See HWSC in Action
Over 80% weed control for species that retain seed at harvest
Crop residue management
There are six systems currently used to collect and manage weed seed at harvest. They can be grouped according to the way crop residue is managed: chaff only or chaff + straw.
Chaff carts are a tow-behind unit on the combine that collects the weed seed-laden chaff, which can then be placed into piles that are later either grazed by livestock, burnt, or both and sown through the following season. Chaff carts are often chosen for use on mixed cropping and livestock farms in Australia as the chaff is an excellent livestock feed; however, spreading manure back onto fields can allow for further seed spread.
Chaff lining funnels the chaff and weed seeds into narrow rows behind the combine, where the residue is left to overwinter. The weed seeds are exposed to natural elements that can lead to weed seed decay and predation. Typically a follow-up herbicide application is required. – Chaff lining is usually considered a good entry-level HWSC option.
Chaff decks (chaff tramlining) are similar to chaff lining, but place the chaff in one or both of the combine’s wheel tracks. The added compaction from the wheels can be beneficial in controlled traffic systems.
Impact mills run the chaff through a mill that pulverizes (destroys) the weed seed, which is then spread across the fields. This technology is usually considered the ultimate in HWSC.
CHAFF + STRAW
Bale direct collects all the crop residue directly from the combine and compacts it into large bales suitable for sale.
Narrow windrow burning collects all of the crop chaff and straw residue, and funnels it into narrow rows in the field. These rows are burnt to destroy the weed seed. This method is effective but removes all of the crop residue from the field.
Learn More About Each System in This Research Report
Calculate the cost
While each HWSC tactic is similarly effective in collecting weed seeds , they vary considerably in capital and ownership cost, nutrient removal costs, operational costs, and labor costs. Some HWSC tactics involve the purchase of substantial machinery – such as an impact mill, chaff cart, or chaff deck – but the operational and labor costs might be lower than methods such as narrow windrow burning, which involves low set-up costs but higher nutrient losses and labor costs associated with burning. Chaff lining is often chosen as the best entry-level tactic that requires minimal set-up cost, no additional labor and minimal nutrient loss or redistribution. To calculate the cost of each method for your farm you can use a calculator developed by WeedSmart’s Peter Newman. Download the calculator or learn more @ Calculating the cost of HWSC for your farm.