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weed and seed rye grass

Cooler weather has set in and your yard is awash with the green of your winter rye lawn. The weeds seem to be swallowed up under the mature growth of this lush green grass. There is a definite connection between the type of lawn you have and the reduction of unwanted growths. Areas of California and other states with mild winters — generally, U.S. Department of Agriculture plant hardiness zones 3 through 9 — can actually support this weed-deterring grass year-round.

There are two types of winter ryegrass. There is the annual variety that you need to replant every year and the more permanent perennial type (Lolium perenne). The grass germinates quickly, within three to five days, and can effectively cover an area within four to eight weeks. It provides a homeowner with a bright green lawn, is great as a filler for bare patches, can mix with other ground cover varieties and assists with erosion control. The weed-repelling ability, though, is one of the biggest advantages to planting this hardy grass in your yard.


Gardeners will often plant ryegrass with other grasses to use this weed-deterring advantage. This grass is commonly grown with zoysia, Bermuda grass and blue grass, depending on water available, type of soil and lawn appearance desired. The seed or sod is also applied to lawns to fill in thinning or bare areas, as well as to take over when cooler weather halts the growth of summer ground cover.

Winter rye grass is an excellent ground cover because it is allelopathic — the grass contains a chemical that will naturally destroy certain weeds and plants that grow in the same soil. Ryegrass planted in the yard can overcome weeds such as duckweed and crabgrass. Take care, though, as ryegrass may overcome other grasses planted in conjunction with it. For example, it can slow the growth of Bermuda grass. Combat this by cutting the ryegrass closer to the ground and reducing the water volume at the end of a cool season in preparation for the emergence of the alternate grass.

Not only can winter rye choke out weeds, but also it can become a weed itself. Rye grass can be resistant to herbicides and be difficult to remove from areas where it is not wanted. Increasing the application of the herbicide glyphosate has proven to be somewhat effective in controlling the spread of this well-known ground cover.

After the second mowing, apply one-half pound of nitrogen per 1000 square feet using a fertilizer, such as 16-4-8 or 15-0-15 (this would be 3 pounds of fertilizer per 1000 square feet of lawn). Apply another one-half pound of nitrogen during mid-winter, if needed to maintain ryegrass color and growth. Pythium blight disease can be a problem on over-watered, over-fertilized ryegrass, especially during warm, humid weather; therefore, it is important to monitor the nitrogen applications and to not over-fertilize or over-water.

Gary Forrester, Horticulture Extension Agent, Horry County Extension Service, Clemson University
Joey Williamson, PhD, HGIC Horticulture Extension Agent, Clemson University

In the spring, mow the ryegrass down to one inch height, which will weaken it and allow the permanent grass to rejuvenate. Be sure to not scalp the permanent lawn as this could also cause a delay in transition (i.e., green up in the spring). When the permanent grass resumes growth, begin regular maintenance, especially fertilization.


If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.

Ryegrass normally dies out in late spring, but if cool weather prevails, it can become persistent. To discourage the ryegrass, fertilizer applications should be made no later than mid- to late January. If possible, allow the lawn to remain on the dry side. This will stress the ryegrass and allow the transition back to warm-season turfgrass. However, do not allow the permanent grass to suffer from lack of water at this time.

It is important to prepare the turfgrass for winter. As temperatures begin to drop in the fall, water demands of turfgrass decrease. Take care not to overwater, as disease problems may increase. Remove any excess thatch so the seed can make good contact with the soil. A heavily thatched lawn tends to result in irregular patches of overseeded grass. Dethatching by verticutting or aerifying will assist overseeding heavily thatched lawns. If core aeration is necessary, overseed thirty days after aeration to allow the holes time to heal and provide an even turf in the winter. For more information on aeration, please see HGIC 1200, Aerating Lawns. Dethatching by verticutting should be performed just prior to overseeding. Mow the lawn closely, catching all clippings or raking afterwards. For more information on dethatching, please see HGIC 2360, Controlling Thatch in Lawns.

Excerpted from Southern Lawns, Bert McCarty (editor) and the University of Florida Extension publication Florida Lawn Handbook.

Gill, G. S. (1996) Ecology of annual ryegrass. Plant Protection Quarterly 11:195-197.

Covered with a stiff outer husk. Brown to yellow or greyish. Cylindrical to oval, 5-7 mm long x 1-2 mm wide. Surface grooved, ridged, hairless. 2-3 mg per seed with an average of 2.8 mg. Seeds tend to remain attached to the stem until mechanically dislodged.

Lolium is from the Greek word for craft, deceitful or treacherous because Darnel (Lolium temulentum) can be toxic and it was believed to be a changed form of wheat.
Annual Ryegrass

Tufted, 100-1200 mm tall, erect, stiff, round and hollow with solid nodes. Often have a reddish tinge and purple on the nodes and at the base. Hairless. Sometime bent at the lower nodes. Flattened where seed spikelets alternate up the stem. Occasional roots at the lower nodes especially in wet conditions.
Tillers profusely and becomes prostrate under grazing. All stems produce seed heads.

Related plants:

It was deliberately planted as a pasture plant or under sown in crops in most southern agricultural areas from the early 1900’s and is still being planted now.

Densities of 30 or more plants/square metre are usually worth spraying in cereals and lupins. This figure for is based on the Annual Ryegrass and crop both being in the 2-3 leaf stage at spraying. If the crop has more leaves than the weed then this figure should be increased to 100 and if the crop has less leaves than the weed then this figure should be reduced to 10 or less. Annual Ryegrass, even at high densities, emerging 3-4 weeks after cereals or lupins rarely affects yields. In cereals, the competition is mainly for nitrogen so early spraying is essential to reduce yield losses. Competition for nitrogen in cereals where the annual ryegrass germinates at the same time as crop from the 2 leaf stage onwards. In Lupins, the competition is for water late in the season so early spraying is not so important.
In lupins, 90 annual ryegrass plants that germinated 6 weeks before the lupins caused 70% grain yield loss, when germinating with the lupins caused 47% yield loss and when germinating 6 weeks after the crop caused no yield loss (Allen, 1977).
The cultivar or variety of cereal has little consistent effect the degree of yield loss caused by Annual Ryegrass. Barley is generally but not always affected less by Annual Ryegrass competition.
The optimum rate of diclofop for ryegrass control can be calculated using the model developed by Pannell (1990) and presented under the economics section of HerbiGuide. This takes into account the weed density, yield potential and prices of grain, application, and herbicide.