Weed Control Seed

The OSU Weed Science Group conducts greenhouse, laboratory and small plot herbicide evaluation trials in support of the development of weed management activities in the diverse cropping systems of Western Oregon. Labeled and experimental herbicides are evaluated for crop safety and weed control efficacy in the following crops: Winter and Spring Wheat, Cool-season Grasses grown 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 So you want to start to kill lawn weeds. To kill weeds in lawn, it helps to know the different types of weeds and the different types of herbicides that specialize in killing them. This article even covers secrets to success, including tips on when to apply weed killers for best results to kills weeds.

Willamette Valley Field Crops

The OSU Weed Science Group conducts greenhouse, laboratory and small plot herbicide evaluation trials in support of the development of weed management activities in the diverse cropping systems of Western Oregon. Labeled and experimental herbicides are evaluated for crop safety and weed control efficacy in the following crops: Winter and Spring Wheat, Cool-season Grasses grown for seed, Native cool-season Grasses and forbs grown for seed, Canola, Meadowfoam, Camelina, Clovers and Peppermint among others.

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Sharp Point Fluvelin

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Weed Science Related Links:

Weed Identification Resources:

Herbicide Labels:

Contact Info

109 Crop Science Building
Oregon State University
Corvallis, OR 97331-3002
Office: (541) 737-2821
Fax: (541) 737-1589

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.

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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.

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*Mention of a specific product does not constitute an endorsement over other products that may be similar

Kill Weeds In Lawns: Begin With The Basics

If you have a yard, you have weeds. They may lurk in the lawn, thrive under a shrub or flourish in flowerbeds, making weed control a constant battle. It requires patience, persistence and knowledge – of both types of weeds and the weapons you have to eradicate them.

What Is A Weed?

A weed is a plant that’s growing where it’s not wanted. Weeds aren’t something you plant intentionally; they just appear. Often they grow vigorously, outpacing and overrunning desirable plants. There are several types of weeds:

Annual Weed: Completes its life cycle – from germination to setting seed – in one growing season; some annual weeds complete their life cycles in a matter of weeks, producing several generations in a single year.

Fact: Annual weed seeds can lie dormant in soil from 4-40 years.

Examples: Chickweed, Crabgrass, Lamb’s-Quarters, Annual bluegrass

Perennial Weed: Lives for two or more years; plants grow as long as conditions are favorable and frequently die back to soil level with hard frost; new growth emerges at the start of the growing season, originating from roots or stem remains; in warmer regions, some perennial weeds can be green year-round.

Fact: Perennial weeds spread by various means, including seed, stems that root as they creep along or pieces of root.

Examples: Creeping Charlie, Curly Dock, Dandelion, Plantain

Broadleaf Weed: Leaves are broad and flat (not grassy or needle-like).

Fact: Broadleaf weeds are easiest to kill or remove when they’re young and actively growing. Some mature broadleaf weeds develop a layer that makes it difficult for weed killers to penetrate.

Examples: Chickweed, Clover, Dandelion, Henbit

Grassy Weed: Looks and grows in ways that resemble grass; leaves are produced one at a time and look like grass blades.

Fact: Many perennial grassy weeds form rhizomes, fleshy roots that resprout if left behind in soil during hand-weeding.

Examples: Bermudagrass, Crabgrass, Giant Foxtail, Goosegrass, Quack Grass

All About Lawn Herbicides

An herbicide is a chemical used to kill weeds or inhibit plant growth. Anytime you use a weed killer, you’re using an herbicide. Some herbicides have residual properties, meaning they continue to kill weeds for a specified time period following application. There are several types of herbicides:

Non-Selective Herbicide: Kills any green and growing plant, whether or not it’s a weed.

Selective Herbicide: Kills only specific types of growing plants; for example, a selective herbicide may kill broadleaf weeds and not grassy plants, so that you can spray it on broadleaf weeds in a lawn without harming grass.

Pre-Emergent Herbicide: Prevents seeds from germinating or kills germinating seeds before seedlings emerge from soil; must be applied before weed seeds germinate. A common example of a pre-emergent herbicide is a Crabgrass preventer, which prevents Crabgrass seeds from establishing new plants.

Post-Emergent Herbicide: Kills weeds that are actively-growing and have already emerged from soil. It’s an ideal herbicide for spot-treating lone offenders but is often applied to entire lawns. Post-emergent herbicides come in two basic forms – contact and systemic.

  • Contact herbicide – only kills the plant parts the chemical touches; ideal for treating annuals and perennial weed seedlings
  • Systemic herbicide – absorbed by leaves, stems or roots of a plant and moves throughout the plant, affecting every part; effective on annuals and established perennial weeds; must be applied when weeds are actively growing
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Specialized Herbicide: To control some especially challenging weeds, like Nutsedge, Clover, Creeping Charlie or Bermudagrass, you’ll want to choose a specific herbicide that’s been proven to be effective. Ask a local garden center or your local Cooperative Extension System office to learn which herbicides will beat your toughest weeds.

Pre-Emergent Secrets to Success

  • Treat the entire area – pre-emergent herbicides create a weed barrier, so if you miss a spot, weeds can sprout there. It’s vital to treat the entire area.
  • Water in – most pre-emergents require watering in, even liquid forms applied using a hose-end sprayer. With liquid herbicides, the volume of water used to disperse the weed killer is not great enough to wash the material into soil, where weed seeds lie waiting to germinate. That’s why you have to water after application.
  • Use caution – when applying pre-emergent herbicides to newly-seeded lawns – or to areas you plan to seed. Read the label carefully. For most products, the label stipulates how many mowings, after seeding, to wait before application. The label also states how long to wait after application before sowing lawn seed.

Post-Emergent Secrets to Success

  • Treat young, actively-growing weeds – they die most easily and create less of an eyesore than mature weeds, which might require repeat applications to completely kill weeds.
  • Inspect the lawn frequently – while mowing is a good time to look for new weeds that have germinated and require treatment.

Timing

For both pre- and post-emergent herbicides, timing is critical. For post-emergent herbicides, you’ll have the best success spraying young, actively-growing weeds. Mature weeds may require repeated applications for total kill. Most post-emergent herbicides should not be applied to dormant lawns. If applying in spring, wait until the lawn is actively growing and has been mowed at least twice.

With pre-emergent herbicides, you’ll want to apply the chemical prior to the time weed seeds start germinating, which can be spring or fall depending on the type of weed. For example: cool-season weeds, such as Annual Bluegrass, are usually best controlled with a late summer to early fall application. If you apply too early, these herbicides will have degraded and are useless when seeds start to germinate. Most pre-emergent Crabgrass killers remain active in soil for 6-8 weeks. If you apply too late, the herbicide will not affect weeds that have already germinated.

Weed seed germination occurs when soil reaches the correct temperature. The best way to determine the ideal time to apply pre-emergents is to contact your local Cooperative Extension System office or master gardeners, who have access to regional soil temperature data.

Other ways to gauge application time include using bioindicators, such as plants whose growth signals the correct time for application. For instance, in northern climates, spring Crabgrass applications are often timed when Forsythia is blooming, which frequently (but not always) occurs when soil temperatures are in the 50°F range. Another option is to time applications based on the calendar. For example, if you typically apply a pre-emergent herbicide in mid-April with success, then continue that routine.

Of course, you can avoid the issue of proper application timing altogether by purchasing a weed control product that combines both pre- and post-emergent herbicides. This type of product kills existing broadleaf weeds and keeps them from returning for as long as six months.