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If you do not plan to do any seeding of turfgrass before fall, certain weeds, such as crabgrass, annual bluegrass, purslane, prostrate pigweed and knotweed, can be treated with a pre-emergence herbicide to keep the seeds from germinating. This will prevent weeds from establishing next spring.
When using pre-emergence herbicides, it is important to know whether the weeds you want to control are annuals, biennials, or perennials. The type of weed it is determines when it germinates, and if the herbicide is applied at the wrong time it will not be effective when the seeds you are targeting are sprouting.
Annuals live for one year and include both summer and winter varieties. Summer annuals such as crabgrass, knotweed and purslane, germinate in the spring, at which time pre-emergence herbicides must be applied. Winter annuals, including bluegrass and common chickweed, germinate in the fall.
Pre-emergence herbicides should be applied in late summer before germination. If you apply pre-emergence herbicides for winter annuals in spring, the herbicide will be broken down by soil microbes before the seeds germinate.
Biennials live for two years. They germinate in one season, pass the winter as a rosette of leaves close to the ground, produce flowers and seeds the second year, then die. Dandelions are usually biennials, although many live for several years. Pre-emergence herbicides are not usually applied strictly for dandelions because seed are produced and germinate throughout the growing season.
Perennials live for two years or more and are difficult to control because they reproduce both from seed and from vegetative buds on the roots. Pre-emergence herbicides have little affect on shoots arising from these vegetative buds, and no effect on vegetative buds of the perennials that have deep root systems. Pre-emergence herbicides are usually applied in spring for germinating perennial seeds. Examples of deep-rooted perennials are field bindweed (the morning glory weed’) and Canada thistle.
Use pre-emergent herbicides only on established lawns, because they will affect most germinating seeds, including desirable ones. Although pre-emergence herbicides are used primarily to control annual grasses, they also help control annual broadleaf weeds, minimizing the need for control of those weeds later in the season. In controlling annual grasses, it is important to positively identify the grass before acting, to avoid wasting time and chemicals treating perennial grasses. Apply chemicals in spring when soil reaches 50???????(R)?F to 55???????(R)?F. Preemergents should be sprayed at the soil level where germination occurs. Once weedy grasses are observed, it is too late for preemergence control. Annual grasses are generally difficult to control once they have infested turf. Selective postemergent control is best accomplished if annual grass seedlings are treated when they are small (i.e., five-leaf stage or younger).
If you are not sure of the identification of a problem weed, take a sample to your county Extension agent or county weed office for identification and appropriate herbicide recommendations. The period of effectiveness varies from two or three weeks to many months.
Adapted from www.landscape-america.com, weeds.montana.edu, 2bnthewild.com, www.invasive.org
Environmentally safe weed control can be a challenge in landscape maintenance. Until recently there were no chemical-free methods to eradicate weeds other than hand-weeding. Corn gluten meal is a natural product that can safely inhibit germination of grass and weed seeds. In 1985, Dr. Nick Christians, of Iowa State University (ISU), accidentally discovered that corn gluten meal had pre-emergence herbicide activity. The control plot of a turf study showed thin seeded grass stands when pure corn gluten was used.
Further study by Dr. Christians and his graduate students lead to 4 patents on corn gluten and its active components over the last 15 years. Currently over 15 companies are licensed by ISU to sell corn gluten as a natural herbicide.
Corn gluten is a by-product of the wet milling process of making cornstarch. Because it contains 60% protein, corn gluten meal is commonly used as an animal feed for cattle, poultry, other livestock, fish and some dog foods.
The meal of corn gluten also contains naturally occurring substances which inhibit the growth of a weed seed’s tiny feeder roots. The treated seedlings struggle to get enough moisture, which causes them to die before they ever have a change to take hold. When used as directed, corn gluten acts as a pre-emergent herbicide that will not harm beneficial insects, soil organisms, pets, or children.
Since corn gluten kills only the roots of sprouting seeds, it can be used around transplants and established vegetables, flowers, fruit, shrubs and lawns. It can be used even up to the day of harvest. Once grass, vegetable, or flower seedlings are established, it is then safe to apply corn gluten.
Corn gluten meal has another benefit for landscapers. It is 10% nitrogen by weight in a slow-release form. As the applied corn gluten decomposes in the soil it adds a substantial amount of plant available nitrogen. In university research, corn gluten treated plants consistently show superior color and quality.
Many manufacturers now supply corn gluten in a granular form for easy application with a standard fertilizer spreader. The recommended rate of application is 20lbs./1000 sq.ft. for lawn grass and up to 40lbs./1000sq.ft. on ornamental plantings.
Grounds managers that are looking for a non-chemical alternative have had success with corn gluten meal. Harley Carter, athletic director at Maharishi School in Fairfield, Iowa learned about corn gluten from Soil Technologies Corp. in Fairfield. The company is a licensee of the ISU patent on corn gluten and markets it’s brand as Dynaweed. The Maharishi School’s unirrigated soccer field was initially seeded in a mix of bluegrass and rye.
“The grass hadn’t grown in well and the field was in dire need of weed control,” he said. “I wanted a natural means of controlling weeds”. After hearing about corn gluten, Carter decided to give it a try. Corn gluten has been applied to the field each spring for 4 years now. “We apply it only in the spring because we’re playing on the field in the fall,” he noted. “It takes time, but there’s no doubt that it works. Our soccer field looks as good as anybody’s in the league now.”
Research suggests that the effectiveness of corn gluten meal improves with every season of use. “Anybody who is looking for an alternative to synthetic herbicides should try it,” says Don Morishita, University of Idaho extension weed scientist, “It’s pretty effective. You have to keep using it, but that’s the case with synthetic herbicides, too.”
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
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